RELIABILITY AND VALIDITY OF THE CARMINATTI’S TEST FOR AEROBIC FITNESS IN YOUTH SOCCER PLAYERS ANDERSON S. TEIXEIRA,1 JULIANO F. DA SILVA,1 LORIVAL J. CARMINATTI,1,2 NAIANDRA DITTRICH,1 CARLO CASTAGNA,3 AND LUIZ G.A. GUGLIELMO1 1
Sports Center, Federal University of Santa Catarina, Physical Effort Laboratory, Floriano´polis, Brazil; 2Morpho-Functional Research Laboratory, Center for Health Sciences and Sports of the University of the State of Santa Catarina, Floriano´polis, Brazil; and 3Football Training and Biomechanics Laboratory, Technical Department, Italian Football Federation (FIGC), Coverciano (Florence), Italy ABSTRACT
Teixeira, AS, da Silva, JF, Carminatti, LJ, Dittrich, N, Castagna, C, and Guglielmo, LGA. Reliability and validity of the Carminatti’s test for aerobic fitness in youth soccer players. J Strength Cond Res 28(11): 3264–3273, 2014—In this study, we examined the reliability and validity of peak velocity determined using the Carminatti’s test (PVT-CAR) to evaluate the aerobic fitness of young soccer players (age = 13.4 6 1.2 years; range, 10.3–15.4 years). To determine test-retest reliability of PVT-CAR, 34 adolescents (U-12, n = 13; U-14, n = 21) performed the Carminatti’s test twice within 3–5 days. Validity was assessed in 43 adolescents (U-14, n = 20; U-16, n = 23) submitted to both the Carminatti’s test and an incremental treadmill test to determine their aerobic fitness indicators. The intraclass correlation of PVT-CAR was 0.89, 0.93, and 0.81 with a coefficient of variation of 2.30% (0.33 km$h21), 1.89% (0.26 km$h21), and 2.66% (0.39 km$h21) for the total sample (pooled data) or separately for the U-12 and U-14 groups, respectively. No significant difference was found between PVT-CAR and maximal aerobic speed (MAS) for the total sample (pooled data) or separately for the U-14 and U-16 groups. In addition, Bland and Altman plots evidenced acceptable agreement between them. The PVT-CAR was significantly related with peak velocity and MAS obtained in the incremental test for the total sample (r = 0.86 and 0.81, p , 0.01, respectively) and separately for the U-14 (r = 0.84 and 0.75, p , 0.01, respectively) and U-16 groups (r = 0.60 and 0.58, p , 0.01, respectively). Furthermore, the PVT-CAR was correlated with the V_ O2peak (r = 0.57, p , 0.01) and the velocity associated to the second ventilatory threshold Address correspondence to Anderson S. Teixeira, anderson.santeixeira@ gmail.com. 28(11)/3264–3273 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
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(r = 0.69, p , 0.01) when the data were pooled (total sample). As a result, the Carminatti’s test may be considered as a reliable and valid measure for assessing and monitoring the development of MAS of young soccer players during adolescence.
KEY WORDS field test, maximal aerobic speed, biological maturation, maturity offset, peak velocity INTRODUCTION
G
iven the intermittent nature of soccer, the physical requirements of the sport impose major demands on the cardiovascular and metabolic capacities of the players (12). Hence, it has been suggested that high values of maximal aerobic power (V_ O2peak) may be an important prerequisite for young soccer players to maintain a high level of activity throughout the game (37). In addition, recently several pieces of evidence have clearly demonstrated the relevance of aerobic fitness and its relationship with physical performance in matches in young soccer players (12,33,37), as well as characterized the pattern of aerobic performance development during the adolescent period (34,38). The development of aerobic performance is influenced by the process of biological maturation and weekly training volume (38), thus practical strategies to accurately assess aerobic fitness under field conditions and to assist in the implementation of soccer-specific and efficient training programs in youth players are required. Consequently, different field tests have been proposed to assess the main components of aerobic fitness with the aim of guiding training prescription, acting as a performance predictor and detecting talent (13,33). Traditionally, the tests performed with fixed distances (i.e., 20 m) such as the Yo-Yo Intermittent Recovery Level 1 (YoYo IR1) and Multistage Fitness Test (MSFT) are characterized by increasing the running intensity at each stage with a decrease in the time interval between audio cues (beep) (25,27). However, recently Carminatti et al. (7) proposed
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Journal of Strength and Conditioning Research a new protocol using progressive distances (i.e., from 15 m with 1 m increments until exhaustion) and fixed audio cues (i.e., 6 seconds) to increase the running velocity. Unlike other tests, in which the total distance covered has been used to represent the test result (25,27), Carminatti’s test (T-CAR) was developed to evaluate aerobic fitness through the peak velocity (PVT-CAR) and allow the direct transference of PVT-CAR as a parameter to be adopted by coaches for training prescription (7). Although the Yo-Yo IR1 and MSFT are well-accepted field tests to assess the intermittent endurance capacity of young athletes, previous studies have shown that the peak velocity determined from these tests underestimate the maximal aerobic speed (MAS) of adolescent soccer and basketball players (15,40). Although equations to predict the MAS have been reported (2), it might be more appropriate to adopt field tests, as T-CAR, for the determination of MAS in team-sport youth players because it provides similar values and is highly correlated with the MAS obtained in the laboratory (8,19,21). In addition, according to Da Silva et al. (19), this protocol with progressive distances allows the athlete to have more distance to accelerate, and thus reach higher values of peak velocity when compared with the models of fixed distance. Regarding the practical implications, it would be possible to prescribe generic aerobic training sessions based on PVT-CAR, allowing several players to work out simultaneously at different running distances according to the individual’s fitness using the same audio cues (i.e., 6 seconds), which in turn seems not to be feasible in protocols such as the MSFT and Yo-Yo IR1 test (19). In this context presented, investigations regarding the reliability and validity of the PVT-CAR as a parameter for predicting MAS and its relationship with other measures of aerobic metabolism, such as peak oxygen uptake (V_ O2peak) and ventilatory thresholds in young soccer players are required before its use by coaches and fitness trainers (24). It is known that minimal measurement error (reliability) of performance of a test refers to the consistency or reproducibility of performance when someone performs the test repeatedly (23). A test with poor reliability is unsuitable for tracking changes in performance between trials, and it lacks precision for the assessment of performance in a single trial (22). However, concurrent validity means that the performance protocol is correlated with a criterion measure (18). However, in pediatric populations, particularly during the transition into adolescence and during adolescence per se, interindividual variability in body size and maturity status in individuals of the same age can directly interfere in this relationship (11), since the influence of chronological age, body size, and biological maturity status on aerobic fitness indices determined in the laboratory (V_ O2peak and ventilatory thresholds) has been reported (10,39). Consequently, the strength of the relationship (concurrent validity) between the laboratory and sport-specific field tests
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(i.e., T-CAR) in young people can be affected by such aforementioned variables. Therefore, it has been recommended that these confounding factors must be properly controlled during statistical analysis (11). As previous reports have been conducted only in adults, studies that have examined the reliability and validity of T-CAR in young soccer players during the pubertal period (10–15 years) still are unknown. Considering the importance of this chronological stage (U-16) in a young soccer player’s development, the resulting information will be of great interest for talent detection and aerobic fitness development. As a working hypothesis, the existence of an association between PVT-CAR (i.e., surrogate measurement) and laboratory assessed criteria of aerobic fitness (i.e., criterion measurement) was assumed. Therefore, the purpose of this study was to determine the test-retest reliability of the PVT-CAR and to examine its relationship with aerobic fitness indices determined in an incremental treadmill laboratory test in young soccer players. The study also examined the relationship between the aerobic tests adjusted for chronological age and estimated biological maturity status, and estimated leg length and fat free mass.
METHODS Experimental Approach to the Problem
In this study, the reliability and criterion-related validity of a contemporary test (T-CAR) developed with the aim of predicting MAS in young soccer players using a progressive distance intermittent shuttle-running protocol was assessed. The reliability of PVT-CAR was based on replicate tests in 2 competitive groups (U-12 and U-14) within a period of 3–5 days. To examine the criterion validity, 2 further competitive groups (U-14 and U-16) performed both the field (T-CAR) and laboratory tests on different days. This study investigated the relationship between PVT-CAR and V_ O2peak, MAS and velocity associated with the second ventilatory threshold (vVT2), using these variables of aerobic fitness as the criterion measurement. Moreover, chronological age, estimated biological maturity status, estimated leg length and fat free mass were statistically controlled to determine if criterion validity and concurrent validity between laboratory and sport-specific field tests were affected by maturation in addition to age and body size descriptors. Subjects
The investigation consisted of 2 studies involving a total of 77 young male soccer players (age = 13.4 6 1.2 years; range, 10.3–15.4 years), who were healthy and injury free were recruited from 2 teams (teams 1 and 2) competing at national level. Participation in the study was voluntary. Players were classified as Under 12 (U-12 = 10.0–11.9 years), 14 (U-14 = 12.0–13.9 years), and 16 (U-16 = 14.0–15.9 years). Players performed 3–5 training sessions per week (each of about 90–120 minutes), participating in an official game at the weekend, usually on Saturday. VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Aerobic Fitness Assessment in Youth Soccer Written informed consent was received from all players and parents/guardians before the study commenced after having been advised, both verbally and in writing, of the risks and benefits involved in this study. All procedures were approved by the ethics committee of the Federal University of Santa Catarina, Brazil (protocol 2004/2011) before this study. Procedures
In study 1, 34 young soccer players belonging to team 1 (U-12, n = 13 and U-14, n = 21) performed the T-CAR test, on 2 independent occasions (T1 and T2) separated by at least 48 hours, to verify the test-retest reliability of the PVT-CAR and individual peak heart rate (HRpeak(T-CAR)). In the week before the experimental measurement (T1 and T2), the players were submitted to one submaximal T-CAR test session for familiarization with the test procedures. All tests were performed toward the end of the competitive season, over a 2-week period. In study 2, 43 young soccer players belonging to team 2 (U-14, n = 20 and U-16, n = 23) performed an incremental treadmill test (ITT) for the assessment of peak treadmill velocity (PVITT), V_ O2peak, MAS, HRpeak(ITT), and vVT2, and the T-CAR test to determine the PVT-CAR and HRpeak(T-CAR). Similarly to study 1, the players were submitted previously to one submaximal T-CAR test session for familiarization with the test procedures. All tests were performed during the preseason period over a 4-week period, with a minimum of 48 hours between tests. Efforts were made to control environmental conditions across the testing sessions. Specifically, for the laboratory assessments air temperature and humidity were kept constant throughout the test duration (i.e., 23–248 C, 50–60% humidity). All tests were performed at the same time of day (i.e., 1400–1800 hours) to avoid the influence of circadian rhythms (9). To avoid undue fatigue before testing, participants were instructed to avoid heavy training during the 24 hours preceding each test. Athletes were advised to maintain a regular diet during the day before testing (i.e., approximately 50–60%, 30–25%, and 20–15% of total energy intake composed of carbohydrates, fat, and protein, respectively) and to refrain from smoking and caffeinated drinks during the 2-hour period preceding testing (21). Participants were allowed to drink water “ad libitum” during the exercises. Chronological age was calculated to the nearest 0.1 year by subtracting birth date from date of testing. Body mass, stature, sitting height, and 2 skinfold thickness (triceps and subscapular) were measured by a single, experienced individual following standard procedures (28). Body mass (in kilograms) was measured to the nearest 0.1 kg using a calibrated scale (Soehnle, Murrhardt, Germany), and stature and sitting height were measured to the nearest 0.1 m with a stadiometer (Sanny, American Medical do Brazil, Sa˜o Paulo, Brazil). Leg length (subischial) was estimated as stature minus sitting height (11). The 2 skinfold thicknesses (triceps and subscapular) were assessed with a scientific
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adipometer accurate to 1 mm (Cescorf, Porto Alegre, Brazil). Percentage body fat was estimated from the triceps and subscapular skinfold thicknesses using the guidelines of Slaughter et al. (36). Fat mass and fat free mass were subsequently calculated (38). Age at peak height velocity (PHV) was estimated with the maturity offset protocol (31). This technique estimates time before or after PHV from chronological age, stature, body mass, sitting height, and estimated leg length. Negative offset values indicated time before PHV and positive values indicated time after PHV. Negative offset values were added to and positive offset values were subtracted from chronological age to estimate age at PHV. Incremental Treadmill Test
An incremental treadmill exercise test was performed on a motorized treadmill (Ibramed Millenium Super, Porto Alegre, Brazil). The treadmill was set at a 1% gradient and an initial starting velocity of 7.2 km$h21; the treadmill velocity was subsequently increased by 0.6 km$h21 every minute until the participants achieved volitional exhaustion. The PVITT was calculated according to the procedures of Kuipers et al. (26) using the following equation: peak velocity (km$h21) = v + t/60; where “v” is the velocity of the last fully completed stage, “t” is the time (in seconds) completed in the partially completed stage, and “60” is the time (in seconds) of a completed stage. Gas analyzer was calibrated immediately before each test using gases of known concentration, and the turbine volume transducer using a 3-L calibration syringe (Quark PFTergo; Cosmed, Rome, Italy). Pulmonary gas exchange response were measured breath by breath during the incremental test using an automated open-circuit gas analysis online metabolic system (Quark PFTergo; Cosmed), and the data were reduced to 15 seconds averages, which were subsequently used for all parameters (35). V_ O2peak was considered as the highest value obtained in a 15-second interval. The HR was recorded continuously during the test from a chest belt transmission connected to the gas analyzer (Cosmed). Peak heart rate was considered the highest 15 seconds average achieved during the test (35). The MAS was identified as the lowest running velocity where the V_ O2peak occurred, as described by Billat et al. (3). Ventilatory thresholds were determined based on plots of ventilation (VE) and the ventilatory equivalents (VE/V_ O2 and VE/V_ CO2) as a function of oxygen uptake and time. Two independent observers blindly detected second ventilatory threshold (VT2) according to the procedures of Dekerle et al. (20), for the subsequent determination of vVT2. Carminatti’s Test
The T-CAR consisted of progressive intermittent shuttle runs of 12 seconds performed between 2 lines set at progressive distances with a 6-second recovery between each run and a total stage time of 90 seconds (7,19,21). The test protocol had a starting velocity of 9 km$h21 over
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the front line for 2 successive repetitions (objective criteria) TABLE 1. Descriptive statistics (mean 6 SD) for the anthropometric or when participants reached characteristics and maturity indicators of youth soccer players (study 1).* volitional exhaustion. The Total sample (n = 34) U-12 (n = 13) U-14 (n = 21) PVT-CAR was calculated from Mean 6 SD Mean 6 SD Mean 6 SD the distance of the last set completed by the athlete Anthropometry divided by the time to comChronological age (y) 12.6 6 1.0 11.5 6 0.4 13.3 6 0.5 plete the stage repetition. In Stature (cm) 152.7 6 10.9 143.4 6 4.3 158.5 6 9.6 Sitting height (cm) 79.0 6 5.5 74.4 6 2.2 81.8 6 4.9 the case of an incomplete set, Estimated leg length (cm) 73.7 6 5.8 69.0 6 2.4 76.6 6 5.2 peak velocity was interpolated Body mass (kg) 43.7 6 11.4 34.8 6 4.7 49.1 6 10.8 using the equation: PV = v + Fat free mass (kg) 36.2 6 8.9 28.9 6 3.4 40.7 6 8.2 (ns/10) 3 0.6, where “v” is the Fat mass (kg) 7.4 6 3.6 5.9 6 2.2 8.4 6 3.9 velocity of the last fully comMaturity indicators Maturity offset (y) 21.3 6 1.1 22.5 6 0.4 20.7 6 0.8 pleted stage and “ns” = number Estimated age at PHV (y) 14.0 6 0.5 13.9 6 0.4 14.0 6 0.6 of repetitions completed in the partially completed stage. *PHV = peak height velocity. Heart rate was monitored at 15-second intervals throughout all the tests with a commercially available telemetry sysa corresponding running distance of 30 m (15 m out and tem (Polar S610; Polar Electro Oy, Kempele, Finland). back). The stage length in a single direction was increased progressively by 1 m every set. Each stage consisted of 5 Statistical Analyses repetitions; between each repetition, there was a 6-second Results are presented as mean 6 SD. The Shapiro-Wilk test walk, which was performed between 2 lines set 2.5 m from and Mauchly’s test were used to verify the normality of the the start line. During the test, 8–10 athletes were evaluated data and spherecity, respectively. The Student’s t-test for simultaneously with the running pace dictated by prerepaired samples was used to compare the mean values of corded audio cues (beeps), which determined the running PVT-CAR and HRpeak(T-CAR) at T1 and T2, as well as the velocity to be performed between the start and finish lines. values of HRpeak(ITT) and HRpeak(T-CAR). In addition, mean The test ended when evaluators observed that the difference and 95% confidence intervals were calculated. An participants failed to keep in time with the audio cues on analysis of variance (ANOVA) with repeated measures was
TABLE 2. Descriptive statistics (mean 6 SD) for the peak velocity and peak heart rate reached in Carminatti’s test with test-retest reliability results (study 1).* Student’s t-test Test 1 Test 2 (mean 6 SD) (mean 6 SD) Total Sample (n = 34) PVT-CAR (km$h21) HRpeak (b$min21) U-12 (n = 13) PVT-CAR (km$h21) HRpeak (b$min21) U-14 (n = 21) PVT-CAR (km$h21) HRpeak (b$min21)
Mean difference (95% CI)
Reliability p
ES
Absolute CV%
Relative ICC (95% CI)
14.3 6 1.0 202.5 6 9.5
14.5 6 1.0 20.2 (20.33 to 0.01) 0.06 0.16 202.1 6 8.9 0.4 (21.79 to 2.61) 0.70 0.05
2.30 2.20
0.89 (0.79 to 0.94) 0.77 (0.58 to 0.88)
13.7 6 1.0 205.0 6 8.0
13.9 6 0.9 20.2 (20.42 to 0.02) 0.08 0.20 205.3 6 8.5 20.3 (24.75 to 4.13) 0.88 0.04
1.89 2.53
0.93 (0.78 to 0.98) 0.79 (0.42 to 0.93)
14.7 6 0.9 14.8 6 0.9 20.1 (20.39 to 0.12) 0.27 0.15 200.9 6 10.3 200.1 6 8.7 0.8 (21.75 to 3.47) 0.50 0.09
2.66 2.02
0.81 (0.58 to 0.92) 0.82 (0.61 to 0.92)
*CV = coefficient of variation; ICC = intraclass correlation coefficient; CI, confidence interval; PVT-CAR = peak velocity obtained from Carminatti’s test; HRpeak = peak heart rate.
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TABLE 3. Descriptive statistics (mean 6 SD) of anthropometric characteristics, maturity indicators, and physiological variables determined in the laboratory and field test for youth soccer players (study 2).* Total sample (43) Mean 6 SD Anthropometry Chronological age (y) Stature (cm) Sitting height (cm) Estimated leg length (cm) Body mass (kg) Fat free mass (kg) Fat mass (kg) Maturity indicators Maturity offset (y) Estimated age at PHV (y) ITT V_ O2peak (ml$kg21$min21) V_ O2peak (L$min21) vVT2 (km$h21) MAS (km$h21) PVITT (km$h21) HRpeak(ITT) (b$min21) Carminatti’s test PVT-CAR (km$h21) HRpeak(T-CAR) (b$min21)
14.0 167.5 86.8 80.7 56.7 49.1 7.5
6 6 6 6 6 6 6
0.9 10.4 5.7 5.8 10.0 8.5 2.4
13.2 160.7 83.0 77.7 49.6 42.9 6.7
0.4 6 1.1 13.7 6 0.5 60.2 3.40 13.8 15.8 16.0 199.6
6 6 6 6 6 6
U-14 (n = 20) Mean 6 SD 6 6 6 6 6 6 6
0.5 9.6 5.4 5.1 9.2 7.4 2.6
U-16 (n = 23) Mean 6 SD 14.7 173.5 90.0 83.5 62.6 54.4 8.3
20.6 6 0.9 13.8 6 0.6
5.2 0.66 1.3 1.4 1.4† 11.4
58.6 2.88 12.8 14.8 15.0 204.2
15.7 6 1.2 201.2 6 9.3
6 6 6 6 6 6
4.6 0.51 1.1 1.1 1.2 9.9
14.9 6 1.1 204.9 6 9.4
6 6 6 6 6 6 6
0.4 7.2 3.6 5.0 6.2 5.3 2.0
1.1 6 0.7 13.5 6 0.4 61.6 3.85 14.6 16.7 16.9 196.7
6 6 6 6 6 6
5.5 0.42 1.0 1.0 0.9† 10.7
16.4 6 0.8 197.6 6 7.9
_ O2peak = peak oxygen uptake; vVT2 = velocity related to second ventilatory threshold; *V MAS = maximal aerobic speed; PVITT = peak velocity determined in incremental treadmill test; HRpeak(ITT) = peak heart rate achieved in incremental treadmill test; PVT-CAR = peak velocity obtained from Carminatti’s test; HRpeak(T-CAR) = peak heart rate reached in Carminatti’s test. †p # 0.05; denotes a significant difference compared with the MAS and PVT-CAR for the total sample and U-16 group (within columns).
used to determine any significant difference between PVITT, MAS, and PVT-CAR. The Bonferroni post hoc test was used when necessary to identify differences. In the case of violation of the assumption of sphericity, the significance was established by using the Greenhouse-Geisser correction. Practical significance was assessed calculating Cohen’s d effect size (ES, 0.1 = trivial, 0.20 = small, 0.5 = medium, 0.8 = large) and partial eta squared (h2, 0.01 = small, 0.06 = medium, 0.14 = large) (13). Pearson’s product-moment correlations between the PVTCAR and laboratory aerobic fitness indicators were calculated first as zero order and then as partial correlations adjusting first for chronological age and maturity offset and then for estimated leg length and fat free mass. The magnitude of effects was qualitatively assessed according to Hopkins (22) as follows: trivial (r , 0.1), small (0.1 , r , 0.3), moderate (0.3 , r , 0.5), large (0.5 , r , 0.7), very large (0.7 , r , 0.9), nearly perfect (r . 0.9). The agreement of the measurements (MAS vs. PVT-CAR and HRpeak(ITT) vs. HRpeak(T-CAR)) was assessed with Bland and Altman plots with variables difference bias tested for
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significance against the null hypothesis (difference = 0). Heteroscedasticity was tested according to Ludbrook (29). Relative and absolute reliability were assessed using the intraclass correlation coefficient (ICC) and typical error of measurement expressed as coefficient of variation (CV%), respectively (23). Statistical significance was set at p # 0.05 for all analyses. The statistical power of total sample size calculated in this study was 0.99–1.00 (correlation analyses), 0.49–0.67 (Student’s t-test), and 0.99 (ANOVA with repeated measures). Calculations were performed with the statistical packages (SPSS 13.5 version; SPSS, Chicago, IL, USA) and GraphPad Prism (GraphPad Prism 5.0 Software Inc., San Diego, CA, USA).
RESULTS Reliability
The anthropometric and maturational characteristics of the young soccer players for the total sample and separately for the groups (U-12 and U-14) are represented in Table 1 (study 1). Table 2 shows the differences between the mean of the 2 test sessions (T1 and T2), ES, CV%, and ICCs of the PVT-CAR and HRpeak(T-CAR) obtained from the T-CAR for the total sample (pooled data) and separately by group (U-12 and U-14). There were no meaningful differences in the mean values of HRpeak(T-CAR) and PVT-CAR between T1 and T2 in either condition (pooled or separately by group). It is important to highlight that for total sample and U-12 group, although the p-value of the PVT-CAR was 0.06 and 0.08, respectively, the practical significance using ES suggests that the differences found at HRpeak(T-CAR) and PVT-CAR between T1 and T2 were trivial to small. Validity
Anthropometric, maturational characteristics, and physiological variables determined in the laboratory and field tests for the total sample and separately by groups (U-14 and U-16) are presented in Table 3 (study 2). In the U-14 group, there were no differences between the PVITT, MAS, and PVT-CAR (F = 0.991; p = 0.355; h2 = 0.05). Otherwise, for the total sample (F = 5.570; p = 0.013;
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sample and U-16, respectively). The HR values referring to TABLE 4. Bivariate and partial correlations of the peak velocity (PVT-CAR) with the incremental laboratory test variables of aerobic fitness, adjusting for CA and MO, and for ELL and FFM.* (HRpeak(ITT)) and T-CAR Partial correlation (HRpeak(T-CAR)) presented no significant difference for the Bivariate correlation CA, MO ELL, FFM total sample (t = 21.06; p = 0.30; ES = 0.15), U-14 (t = Total sample (n = 43) 0.46† 0.36† 0.45† PVT-CAR vs. V_ O2peak (ml$kg21$min21) 20.72; p = 0.48; ES = 0.07) 0.57z 0.31z 0.44† PVT-CAR vs. V_ O2peak (L$min21) and U-16 groups (t = 20.77; PVT-CAR vs. vVT2 0.69z 0.48z 0.59z p = 0.45; ES = 0.10), with PVT-CAR vs. MAS 0.81z 0.63z 0.68z a very large correlation (r = PVT-CAR vs. PVITT 0.86z 0.72z 0.78z 0.89, 0.90, and 0.86 for the total U-14 (n = 20) PVT-CAR vs. V_ O2peak (ml$kg21$min21) 0.48† 0.48† 0.74z sample, U-14 and U-16 groups, PVT-CAR vs. V_ O2peak (L$min21) 0.14 0.23 0.54† respectively; p , 0.01). PVT-CAR vs. vVT2 0.53† 0.53† 0.40 The correlations of PVT-CAR 0.75z 0.73z 0.73z PVT-CAR vs. MAS with the aerobic fitness variaPVT-CAR vs. PVITT 0.84z 0.82z 0.82z bles determined in the laboraU-16 (n = 23) PVT-CAR vs. V_ O2peak (ml$kg21$min21) 0.28 0.38 0.30 tory for the total sample and PVT-CAR vs. V_ O2peak (L$min21) 0.30 0.45 0.38 separately by group (U-14 PVT-CAR vs. vVT2 0.40 0.30 0.40 and U-16) are summarized in PVT-CAR vs. MAS 0.58z 0.62z 0.60z Table 4 (study 2). 0.60z 0.57z 0.61z PVT-CAR vs. PVITT The PVT-CAR was signifi*CA = chronological age; MO = maturity offset; ELL = estimated leg length; FFM = fat free cantly correlated with the mass; V_ O2peak = peak oxygen uptake; vVT2 = velocity related to second ventilatory threshold; and MAS for the total PV ITT MAS = maximal aerobic speed; PVITT = peak velocity determined in incremental treadmill test; sample and in both groups PVT-CAR = peak velocity obtained from Carminatti’s test. †p # 0.05. (U-14 and U-16). It was zp , 0.01. noticed that the PVT-CAR was significantly correlated to the vVT2 only for the total sample and the U-14 group. These correlation values did not change after adjustment for chroh2 = 0.12) and in U-16 group (F = 7.367; p = 0.005; h2 = nological age, biological maturity, and body size. The bivar0.25) differences were found. The results of pairwise comiate correlation between the PVT-CAR and V_ O2peak was only parisons showed values significantly higher for the PVITT meaningful for the total sample and U-14 group. When the compared with the MAS (p = 0.001 and p = 0.013; total body size descriptors were controlled, the correlation values sample and U-16 group, respectively) and PVT-CAR (p = increased for the relative V_ O2peak (r = 0.74) and absolute 0.015 and p = 0.005; total sample and U-16 group, respecV_ O2peak (r = 0.54) in the U-14 group, while remaining tively). However, no differences were observed between the unchanged for the total sample. Specifically in the U-16 MAS and the PVT-CAR (p = 1.000 and p = 0.459, for the total
Figure 1. Scatter plot of PVITT (km$h21) and PVT-CAR (km$h21) for total sample, U-14 and U-16 groups. SEE = standard error of estimate.
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Aerobic Fitness Assessment in Youth Soccer
Figure 2. Bland-Altman plot of MAS vs. PVT-CAR (upper panels) and HRpeak(ITT) vs. HRpeak(T-CAR) (lower panels). Dotted lines represent the bias and solid lines denote lower and upper 95% limits of agreement.
group, this relationship was observed only between the PVT-CAR and the relative V_ O2peak (r = 0.45) after adjusting for chronological age and maturity offset (Table 4). Relationship between PVT-CAR and PVITT for the total sample, U-14 and U-16 groups, predictive equation, coefficient of determination (R2), and standard error of estimate are illustrated in Figure 1. Linear relationship was observed between PVT-CAR and PVITT in each condition (i.e., pooled data or separately by group). Additionally, Figure 2 shows the bias 695% limits of agreement for the comparison between the MAS and PVT-CAR (0.08 6 1.62, 20.12 6 1.56, and 0.26 6 1.63 km.hour21) and the HRpeak(ITT) and HRpeak(T-CAR) (20.24 6 8.64, 20.70 6 8.60, and 0.19 6 8.84 b$min21) for the total sample, U-14 and U-16 groups, respectively. It should be noted that there was no systematic error (heteroscedasticity) for agreement measures between the physiological variables determined in the laboratory and field tests.
DISCUSSION The primary aim of this investigation was to assess the reliability and concurrent validity of PVT-CAR in young soccer players classified as U-12, U-14, and U-16. The results of the current study showed that PVT-CAR may be considered as a predictor of MAS. Indeed, the PVT-CAR was largely to very largely correlated with PVITT, MAS, V_ O2peak, and vVT2. Furthermore, PVT-CAR and HRpeak(T-CAR) showed a good relative and absolute reliability in both competitive age groups analyzed (U-12 and U-14). These findings
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provide evidence that T-CAR may be considered as an appropriate test for the assessment of aerobic fitness under field conditions in young soccer players of different competitive age groups. Short-term relative and absolute reliability are relevant measures of test applicability (14). Clinical studies suggested that tests providing CV% and ICC values lower than 10% and higher than 0.75 respectively, should be considered as able to determine practical acceptance of clinical variations (17). In this study, the ICC (0.81–0.93, good to excellent) and CV% (1.9–2.7%) values for PVT-CAR in both groups (U-12 and U-14) showed that the T-CAR was a reliable test in the specific experimental set-up considered. Additionally, the low CV% values suggest relatively small within-subject variation between trials. Familiarization with the testing protocol may have contributed to the high reliability of PVT-CAR. The reported CV% for PVT-CAR was slightly lower than that reported for performance in the Yo-Yo IR1 (3.8%) and MSFT (3.6%) in 18 young Italian soccer players (16). Similarly, the reliability values in this investigation were consistent with those reported for T-CAR short-term repeated measure design in male junior competitive match level soccer players whose ICC and CV% were 0.94 (good to excellent) and 1.3%, respectively (19). These results strongly demonstrate that T-CAR requires only a small familiarization to provide reliable data. Another important finding of this study was the good HRpeak(T-CAR) reliability (ICC = 0.79 and 0.83, CV = 2.5 and 2.0%; for the U-12 and U-14 groups, respectively) obtained
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Journal of Strength and Conditioning Research from T-CAR in young soccer players. Similar values of relative and absolute reliability were obtained when the data were pooled (total sample; Table 2). Additionally, the HRpeak found in the ITT and the HRpeak obtained in T-CAR were shown to be very largely associated (r = 0.90 and 0.86, for the U-14 and U-16 groups, respectively; p , 0.001) and not significantly different (p . 0.05; Table 3) within each group (U-14 and U-16). Interestingly, the interpretation of 695% limits of agreement constructed from the analysis of these 2 measures (HRpeak(T-CAR) vs. HRpeak(ITT); lower panels; Figure 2) suggests that if the HRpeak(ITT) were to be estimated from HRpeak reached during the T-CAR for a single participant a variation of up to 69 b$min21 or 64.2% could be visualized. This individual variation in the HRpeak(T-CAR) of youth soccer players has practical relevance to coaches because it can be used to estimate the HRpeak(ITT), and therefore be used to control the internal training load and identify the target zones (i.e., ;90% HRpeak) of generic aerobic training (interval training) and specific training (i.e., small sided games) for the development of aerobic fitness (5). The concurrent validity of the T-CAR was performed examining the association (i.e., correlation) of PVT-CAR with PVITT, MAS, V_ O2peak, and vVT2 (i.e., criterion measurement) achieved during a standard treadmill test and comparing PVT-CAR with MAS (i.e., reference variable), characterized in this study as the MAS achieved during the treadmill test (3). Relative mean values for V_ O2peak show that players from both groups (U-14 and U-16) had a high degree of aerobic fitness, particularly when compared with values reported for males of similar ages in the general population (30). Significant differences between PVT-CAR and MAS in the U-14 (14.9 6 1.1 vs. 14.8 6 1.1 km$h21, p = 1.00) and U-16 groups (16.4 6 0.8 vs. 16.7 6 1.0 km$h21, p = 0.46) were not found. It should be noted that the same results were obtained when the data were pooled (total sample). However, the average values of PVT-CAR and PVITT presented significant differences in the U-16 group and total sample (for more details see Table 3). Similar findings have been reported showing that the peak velocity determined in treadmill tests is higher than that reached in field tests, specifically due to the constant direction changes, which contribute to a reduced running economy (4,19,21). Moreover, previous studies using the MSFT and Yo-Yo IR1 have found that the peak velocity obtained with fixed distance protocols in youth soccer and basketball players also underestimates the MAS (vV_ O2max) (15,40), which is different to the present findings. In this perspective, the additional contribution of T-CAR compared with other protocols is the ability to estimate and/or predict the velocity that corresponds to maximal aerobic power (i.e., MAS) in well-trained young soccer players (i.e., V_ O2peak $60.2 ml$kg21$min21) under field conditions (test applicability). It could be speculated that the higher peak velocity obtainable in T-CAR compared
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to other field tests is probably due to a combination of two factors (19). First, the higher peak velocity reached in T-CAR could be related to the work rest ratio considered. Second, the considered distance increment at each stage, which enables greater distances (;25–27 m) to be covered by players during the final test stages, compared with other tests (20 m), may reduce the time spent accelerating and decelerating after each turn. This test characteristic would reduce the occurrence of neuromuscular fatigue. Moreover, the higher energetic cost of running over shorter distances (i.e., 20 m) (6), could also explain the higher values of peak velocity during T-CAR. Furthermore, it was observed that for both groups (U-14 and U-16), the PVT-CAR was significantly correlated to the PVITT, MAS, and V_ O2peak (aerobic power indices). However, the association between the PVT-CAR and vVT2 (aerobic capacity index) was observed only in the U-14 group (Table 4). Interestingly, these relationships tended to remain unchanged for most analyses after control for the influence of age, biological maturity, and body size, suggesting that the relationship between the PVT-CAR and the physiological indices of aerobic fitness does not seem to be affected by growing or biological maturity. However, the relationship between PVT-CAR and V_ O2peak increased significantly in the U-14 group after adjusting for estimated leg length and fat free mass (Table 4), showing that this relationship seems to be dependent on body size descriptors in young soccer players around the PHV (Table 3). As a complementary result, the agreement analysis between MAS and PVT-CAR was performed using the Bland and Altman plots (Figure 2). This information is of critical importance for coaches who want to use field tests to monitor changes in young players’ fitness and guide training prescription. This statistical method has been widely used in the sports science area to evaluate the performance measures relevant to different sports (1,13). It should be noted that, in this study, the bias and limits of agreement between MAS and PVT-CAR (upper panels; Figure 2) for the total sample (0.08 6 1.62 km$h21) or separately for the U-14 (20.12 6 1.56 km$h21) and U-16 groups (0.26 6 1.63 km$h21) were similar to the peak velocity values found in the 45-15 test (20.20 6 1.7 km$h21) in Italian youth soccer players (25). To the best of our knowledge, this is the first study to show the intraindividual variation in the estimative of MAS from PVT-CAR in youth soccer players from different competitive categories (U-14 and U-16). Although there can be multiple sources of error when measurements are made in the sport and exercise sciences (1), a possible explanation for the variations found in this study can be attributed to the specific characteristics (intermittent vs. continuous) of each protocol in which the PVT-CAR and MAS were determined. In this sense, the limits of agreement in PVT-CAR for both groups (U-14 and U-16) have an acceptable practical significance for predicting MAS, however, should be used with caution to individualize the VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Aerobic Fitness Assessment in Youth Soccer training intensities, making adjustments in PVT-CAR to correct these variations inherent in the protocol. Therefore, T-CAR seems to be an interesting test of practical relevance to assess aerobic fitness and to prescribe generic (PVT-CAR) and specific (individual HRpeak) training in young soccer players during adolescence, since longitudinal studies have shown that the highest gain in aerobic fitness occurs, on average, close to the PHV age (32). However, further studies are needed to examine the effect of using the PVT-CAR (high-intensity intermittent running) as a training tool for the aerobic fitness of young soccer players. Moreover, future investigations examining the influence of growth and maturation on the performance in T-CAR of young soccer players are required.
PRACTICAL APPLICATIONS Carminatti’s test (T-CAR) can be considered a valid field test to estimate the MAS based on the PVT-CAR, and also to estimate the HRpeak of young soccer players. These findings enable coaches to monitor and evaluate the development of the aerobic performance of young soccer players during adolescence. The good reliability and validity of the HRpeak(T-CAR) found in this study enables the use of this indirect measure as an important parameter to control the internal training load during functional and generic training sessions designed to develop aerobic fitness in youth soccer players. Additionally, the PVT-CAR can be used by coaches in the prescription of high-intensity intermittent training models in children and adolescents simultaneously using the same audio cue, as well as to monitor performance improvements induced during the competitive season, given the high reliability of PVTCAR. Therefore, these results should be of interest to coaches, sport scientists, and others involved in the selection and development of youth soccer players.
ACKNOWLEDGMENTS We gratefully appreciate the patience and cooperation of the young athletes, coaches, and parents during the execution of this study and the National Council of Technological and Scientific Development (CNPq/Brazil) for financial support.
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33. Rebelo, A, Brito, J, Seabra, A, Oliveira, J, and Krustrup, P. Physical match performance of youth football players in relation to physical capacity. Eur J Sport Sci 14: S148–S156, 2014. 34. Roescher, CR, Elferink-Gemser, MT, Huijgen, BCH, and Visscher, C. Soccer endurance development in professionals. Int J Sports Med 31: 174–179, 2010. 35. Saynor, ZL, Barker, AR, Oades, PJ, and Williams, CA. A protocol to determine valid VO2max in young cystic fibrosis patients. J Sci Med Sport 16: 539–544, 2013. 36. Slaughter, MH, Lohman, TG, Boileau, RA, Horswill, CA, Stillman, RJ, Van Loan, MD, and Bemben, DA. Skinfold equations for estimation of body fatness in children and youth. Hum Biol 60: 709–723, 1988. 37. Strøyer, J, Hansen, L, and Klausen, K. Physiological profile and activity pattern of young soccer players during match play. Med Sci Sports Exerc 36: 168–174, 2004. 38. Valente dos Santos, J, Coelho e Silva, MJ, Duarte, J, Figueiredo, AJ, Liparotti, JR, Sherar, LB, Elferink-Gemser, MT, and Malina, RM. Longitudinal predictors of aerobic performance in adolescent soccer players. Medicina (Kaunas) 48: 410–416, 2012. 39. Valente dos Santos, J, Sherar, L, Coelho-e-Silva, MJ, Pereira, JR, Vaz, V, Cupido-dos-Santos, A, Baxter-Jones, A, Visscher, C, ElferinkGemser, MT, and Malina, RM. Allometric scaling of peak oxygen uptake in male roller hockey players under 17 years old. Appl Physiol Nutr Metab 38: 390–395, 2013. 40. Williford, HN, Scharff-Olson, M, Duey, WJ, Pugh, S, and Barksdale, JM. Physiological status and prediction of cardiovascular fitness in highly trained youth soccer athletes. J Strength Cond Res 13: 10–15, 1999.
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Sports Center, Federal University of Santa Catarina, Physical Effort Laboratory, Floriano´polis, Brazil; 2Morpho-Functional Research Laboratory, Center for Health Sciences and Sports of the University of the State of Santa Catarina, Floriano´polis, Brazil; and 3Football Training and Biomechanics Laboratory, Technical Department, Italian Football Federation (FIGC), Coverciano (Florence), Italy ABSTRACT
Teixeira, AS, da Silva, JF, Carminatti, LJ, Dittrich, N, Castagna, C, and Guglielmo, LGA. Reliability and validity of the Carminatti’s test for aerobic fitness in youth soccer players. J Strength Cond Res 28(11): 3264–3273, 2014—In this study, we examined the reliability and validity of peak velocity determined using the Carminatti’s test (PVT-CAR) to evaluate the aerobic fitness of young soccer players (age = 13.4 6 1.2 years; range, 10.3–15.4 years). To determine test-retest reliability of PVT-CAR, 34 adolescents (U-12, n = 13; U-14, n = 21) performed the Carminatti’s test twice within 3–5 days. Validity was assessed in 43 adolescents (U-14, n = 20; U-16, n = 23) submitted to both the Carminatti’s test and an incremental treadmill test to determine their aerobic fitness indicators. The intraclass correlation of PVT-CAR was 0.89, 0.93, and 0.81 with a coefficient of variation of 2.30% (0.33 km$h21), 1.89% (0.26 km$h21), and 2.66% (0.39 km$h21) for the total sample (pooled data) or separately for the U-12 and U-14 groups, respectively. No significant difference was found between PVT-CAR and maximal aerobic speed (MAS) for the total sample (pooled data) or separately for the U-14 and U-16 groups. In addition, Bland and Altman plots evidenced acceptable agreement between them. The PVT-CAR was significantly related with peak velocity and MAS obtained in the incremental test for the total sample (r = 0.86 and 0.81, p , 0.01, respectively) and separately for the U-14 (r = 0.84 and 0.75, p , 0.01, respectively) and U-16 groups (r = 0.60 and 0.58, p , 0.01, respectively). Furthermore, the PVT-CAR was correlated with the V_ O2peak (r = 0.57, p , 0.01) and the velocity associated to the second ventilatory threshold Address correspondence to Anderson S. Teixeira, anderson.santeixeira@ gmail.com. 28(11)/3264–3273 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
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(r = 0.69, p , 0.01) when the data were pooled (total sample). As a result, the Carminatti’s test may be considered as a reliable and valid measure for assessing and monitoring the development of MAS of young soccer players during adolescence.
KEY WORDS field test, maximal aerobic speed, biological maturation, maturity offset, peak velocity INTRODUCTION
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iven the intermittent nature of soccer, the physical requirements of the sport impose major demands on the cardiovascular and metabolic capacities of the players (12). Hence, it has been suggested that high values of maximal aerobic power (V_ O2peak) may be an important prerequisite for young soccer players to maintain a high level of activity throughout the game (37). In addition, recently several pieces of evidence have clearly demonstrated the relevance of aerobic fitness and its relationship with physical performance in matches in young soccer players (12,33,37), as well as characterized the pattern of aerobic performance development during the adolescent period (34,38). The development of aerobic performance is influenced by the process of biological maturation and weekly training volume (38), thus practical strategies to accurately assess aerobic fitness under field conditions and to assist in the implementation of soccer-specific and efficient training programs in youth players are required. Consequently, different field tests have been proposed to assess the main components of aerobic fitness with the aim of guiding training prescription, acting as a performance predictor and detecting talent (13,33). Traditionally, the tests performed with fixed distances (i.e., 20 m) such as the Yo-Yo Intermittent Recovery Level 1 (YoYo IR1) and Multistage Fitness Test (MSFT) are characterized by increasing the running intensity at each stage with a decrease in the time interval between audio cues (beep) (25,27). However, recently Carminatti et al. (7) proposed
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Journal of Strength and Conditioning Research a new protocol using progressive distances (i.e., from 15 m with 1 m increments until exhaustion) and fixed audio cues (i.e., 6 seconds) to increase the running velocity. Unlike other tests, in which the total distance covered has been used to represent the test result (25,27), Carminatti’s test (T-CAR) was developed to evaluate aerobic fitness through the peak velocity (PVT-CAR) and allow the direct transference of PVT-CAR as a parameter to be adopted by coaches for training prescription (7). Although the Yo-Yo IR1 and MSFT are well-accepted field tests to assess the intermittent endurance capacity of young athletes, previous studies have shown that the peak velocity determined from these tests underestimate the maximal aerobic speed (MAS) of adolescent soccer and basketball players (15,40). Although equations to predict the MAS have been reported (2), it might be more appropriate to adopt field tests, as T-CAR, for the determination of MAS in team-sport youth players because it provides similar values and is highly correlated with the MAS obtained in the laboratory (8,19,21). In addition, according to Da Silva et al. (19), this protocol with progressive distances allows the athlete to have more distance to accelerate, and thus reach higher values of peak velocity when compared with the models of fixed distance. Regarding the practical implications, it would be possible to prescribe generic aerobic training sessions based on PVT-CAR, allowing several players to work out simultaneously at different running distances according to the individual’s fitness using the same audio cues (i.e., 6 seconds), which in turn seems not to be feasible in protocols such as the MSFT and Yo-Yo IR1 test (19). In this context presented, investigations regarding the reliability and validity of the PVT-CAR as a parameter for predicting MAS and its relationship with other measures of aerobic metabolism, such as peak oxygen uptake (V_ O2peak) and ventilatory thresholds in young soccer players are required before its use by coaches and fitness trainers (24). It is known that minimal measurement error (reliability) of performance of a test refers to the consistency or reproducibility of performance when someone performs the test repeatedly (23). A test with poor reliability is unsuitable for tracking changes in performance between trials, and it lacks precision for the assessment of performance in a single trial (22). However, concurrent validity means that the performance protocol is correlated with a criterion measure (18). However, in pediatric populations, particularly during the transition into adolescence and during adolescence per se, interindividual variability in body size and maturity status in individuals of the same age can directly interfere in this relationship (11), since the influence of chronological age, body size, and biological maturity status on aerobic fitness indices determined in the laboratory (V_ O2peak and ventilatory thresholds) has been reported (10,39). Consequently, the strength of the relationship (concurrent validity) between the laboratory and sport-specific field tests
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(i.e., T-CAR) in young people can be affected by such aforementioned variables. Therefore, it has been recommended that these confounding factors must be properly controlled during statistical analysis (11). As previous reports have been conducted only in adults, studies that have examined the reliability and validity of T-CAR in young soccer players during the pubertal period (10–15 years) still are unknown. Considering the importance of this chronological stage (U-16) in a young soccer player’s development, the resulting information will be of great interest for talent detection and aerobic fitness development. As a working hypothesis, the existence of an association between PVT-CAR (i.e., surrogate measurement) and laboratory assessed criteria of aerobic fitness (i.e., criterion measurement) was assumed. Therefore, the purpose of this study was to determine the test-retest reliability of the PVT-CAR and to examine its relationship with aerobic fitness indices determined in an incremental treadmill laboratory test in young soccer players. The study also examined the relationship between the aerobic tests adjusted for chronological age and estimated biological maturity status, and estimated leg length and fat free mass.
METHODS Experimental Approach to the Problem
In this study, the reliability and criterion-related validity of a contemporary test (T-CAR) developed with the aim of predicting MAS in young soccer players using a progressive distance intermittent shuttle-running protocol was assessed. The reliability of PVT-CAR was based on replicate tests in 2 competitive groups (U-12 and U-14) within a period of 3–5 days. To examine the criterion validity, 2 further competitive groups (U-14 and U-16) performed both the field (T-CAR) and laboratory tests on different days. This study investigated the relationship between PVT-CAR and V_ O2peak, MAS and velocity associated with the second ventilatory threshold (vVT2), using these variables of aerobic fitness as the criterion measurement. Moreover, chronological age, estimated biological maturity status, estimated leg length and fat free mass were statistically controlled to determine if criterion validity and concurrent validity between laboratory and sport-specific field tests were affected by maturation in addition to age and body size descriptors. Subjects
The investigation consisted of 2 studies involving a total of 77 young male soccer players (age = 13.4 6 1.2 years; range, 10.3–15.4 years), who were healthy and injury free were recruited from 2 teams (teams 1 and 2) competing at national level. Participation in the study was voluntary. Players were classified as Under 12 (U-12 = 10.0–11.9 years), 14 (U-14 = 12.0–13.9 years), and 16 (U-16 = 14.0–15.9 years). Players performed 3–5 training sessions per week (each of about 90–120 minutes), participating in an official game at the weekend, usually on Saturday. VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Aerobic Fitness Assessment in Youth Soccer Written informed consent was received from all players and parents/guardians before the study commenced after having been advised, both verbally and in writing, of the risks and benefits involved in this study. All procedures were approved by the ethics committee of the Federal University of Santa Catarina, Brazil (protocol 2004/2011) before this study. Procedures
In study 1, 34 young soccer players belonging to team 1 (U-12, n = 13 and U-14, n = 21) performed the T-CAR test, on 2 independent occasions (T1 and T2) separated by at least 48 hours, to verify the test-retest reliability of the PVT-CAR and individual peak heart rate (HRpeak(T-CAR)). In the week before the experimental measurement (T1 and T2), the players were submitted to one submaximal T-CAR test session for familiarization with the test procedures. All tests were performed toward the end of the competitive season, over a 2-week period. In study 2, 43 young soccer players belonging to team 2 (U-14, n = 20 and U-16, n = 23) performed an incremental treadmill test (ITT) for the assessment of peak treadmill velocity (PVITT), V_ O2peak, MAS, HRpeak(ITT), and vVT2, and the T-CAR test to determine the PVT-CAR and HRpeak(T-CAR). Similarly to study 1, the players were submitted previously to one submaximal T-CAR test session for familiarization with the test procedures. All tests were performed during the preseason period over a 4-week period, with a minimum of 48 hours between tests. Efforts were made to control environmental conditions across the testing sessions. Specifically, for the laboratory assessments air temperature and humidity were kept constant throughout the test duration (i.e., 23–248 C, 50–60% humidity). All tests were performed at the same time of day (i.e., 1400–1800 hours) to avoid the influence of circadian rhythms (9). To avoid undue fatigue before testing, participants were instructed to avoid heavy training during the 24 hours preceding each test. Athletes were advised to maintain a regular diet during the day before testing (i.e., approximately 50–60%, 30–25%, and 20–15% of total energy intake composed of carbohydrates, fat, and protein, respectively) and to refrain from smoking and caffeinated drinks during the 2-hour period preceding testing (21). Participants were allowed to drink water “ad libitum” during the exercises. Chronological age was calculated to the nearest 0.1 year by subtracting birth date from date of testing. Body mass, stature, sitting height, and 2 skinfold thickness (triceps and subscapular) were measured by a single, experienced individual following standard procedures (28). Body mass (in kilograms) was measured to the nearest 0.1 kg using a calibrated scale (Soehnle, Murrhardt, Germany), and stature and sitting height were measured to the nearest 0.1 m with a stadiometer (Sanny, American Medical do Brazil, Sa˜o Paulo, Brazil). Leg length (subischial) was estimated as stature minus sitting height (11). The 2 skinfold thicknesses (triceps and subscapular) were assessed with a scientific
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adipometer accurate to 1 mm (Cescorf, Porto Alegre, Brazil). Percentage body fat was estimated from the triceps and subscapular skinfold thicknesses using the guidelines of Slaughter et al. (36). Fat mass and fat free mass were subsequently calculated (38). Age at peak height velocity (PHV) was estimated with the maturity offset protocol (31). This technique estimates time before or after PHV from chronological age, stature, body mass, sitting height, and estimated leg length. Negative offset values indicated time before PHV and positive values indicated time after PHV. Negative offset values were added to and positive offset values were subtracted from chronological age to estimate age at PHV. Incremental Treadmill Test
An incremental treadmill exercise test was performed on a motorized treadmill (Ibramed Millenium Super, Porto Alegre, Brazil). The treadmill was set at a 1% gradient and an initial starting velocity of 7.2 km$h21; the treadmill velocity was subsequently increased by 0.6 km$h21 every minute until the participants achieved volitional exhaustion. The PVITT was calculated according to the procedures of Kuipers et al. (26) using the following equation: peak velocity (km$h21) = v + t/60; where “v” is the velocity of the last fully completed stage, “t” is the time (in seconds) completed in the partially completed stage, and “60” is the time (in seconds) of a completed stage. Gas analyzer was calibrated immediately before each test using gases of known concentration, and the turbine volume transducer using a 3-L calibration syringe (Quark PFTergo; Cosmed, Rome, Italy). Pulmonary gas exchange response were measured breath by breath during the incremental test using an automated open-circuit gas analysis online metabolic system (Quark PFTergo; Cosmed), and the data were reduced to 15 seconds averages, which were subsequently used for all parameters (35). V_ O2peak was considered as the highest value obtained in a 15-second interval. The HR was recorded continuously during the test from a chest belt transmission connected to the gas analyzer (Cosmed). Peak heart rate was considered the highest 15 seconds average achieved during the test (35). The MAS was identified as the lowest running velocity where the V_ O2peak occurred, as described by Billat et al. (3). Ventilatory thresholds were determined based on plots of ventilation (VE) and the ventilatory equivalents (VE/V_ O2 and VE/V_ CO2) as a function of oxygen uptake and time. Two independent observers blindly detected second ventilatory threshold (VT2) according to the procedures of Dekerle et al. (20), for the subsequent determination of vVT2. Carminatti’s Test
The T-CAR consisted of progressive intermittent shuttle runs of 12 seconds performed between 2 lines set at progressive distances with a 6-second recovery between each run and a total stage time of 90 seconds (7,19,21). The test protocol had a starting velocity of 9 km$h21 over
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the front line for 2 successive repetitions (objective criteria) TABLE 1. Descriptive statistics (mean 6 SD) for the anthropometric or when participants reached characteristics and maturity indicators of youth soccer players (study 1).* volitional exhaustion. The Total sample (n = 34) U-12 (n = 13) U-14 (n = 21) PVT-CAR was calculated from Mean 6 SD Mean 6 SD Mean 6 SD the distance of the last set completed by the athlete Anthropometry divided by the time to comChronological age (y) 12.6 6 1.0 11.5 6 0.4 13.3 6 0.5 plete the stage repetition. In Stature (cm) 152.7 6 10.9 143.4 6 4.3 158.5 6 9.6 Sitting height (cm) 79.0 6 5.5 74.4 6 2.2 81.8 6 4.9 the case of an incomplete set, Estimated leg length (cm) 73.7 6 5.8 69.0 6 2.4 76.6 6 5.2 peak velocity was interpolated Body mass (kg) 43.7 6 11.4 34.8 6 4.7 49.1 6 10.8 using the equation: PV = v + Fat free mass (kg) 36.2 6 8.9 28.9 6 3.4 40.7 6 8.2 (ns/10) 3 0.6, where “v” is the Fat mass (kg) 7.4 6 3.6 5.9 6 2.2 8.4 6 3.9 velocity of the last fully comMaturity indicators Maturity offset (y) 21.3 6 1.1 22.5 6 0.4 20.7 6 0.8 pleted stage and “ns” = number Estimated age at PHV (y) 14.0 6 0.5 13.9 6 0.4 14.0 6 0.6 of repetitions completed in the partially completed stage. *PHV = peak height velocity. Heart rate was monitored at 15-second intervals throughout all the tests with a commercially available telemetry sysa corresponding running distance of 30 m (15 m out and tem (Polar S610; Polar Electro Oy, Kempele, Finland). back). The stage length in a single direction was increased progressively by 1 m every set. Each stage consisted of 5 Statistical Analyses repetitions; between each repetition, there was a 6-second Results are presented as mean 6 SD. The Shapiro-Wilk test walk, which was performed between 2 lines set 2.5 m from and Mauchly’s test were used to verify the normality of the the start line. During the test, 8–10 athletes were evaluated data and spherecity, respectively. The Student’s t-test for simultaneously with the running pace dictated by prerepaired samples was used to compare the mean values of corded audio cues (beeps), which determined the running PVT-CAR and HRpeak(T-CAR) at T1 and T2, as well as the velocity to be performed between the start and finish lines. values of HRpeak(ITT) and HRpeak(T-CAR). In addition, mean The test ended when evaluators observed that the difference and 95% confidence intervals were calculated. An participants failed to keep in time with the audio cues on analysis of variance (ANOVA) with repeated measures was
TABLE 2. Descriptive statistics (mean 6 SD) for the peak velocity and peak heart rate reached in Carminatti’s test with test-retest reliability results (study 1).* Student’s t-test Test 1 Test 2 (mean 6 SD) (mean 6 SD) Total Sample (n = 34) PVT-CAR (km$h21) HRpeak (b$min21) U-12 (n = 13) PVT-CAR (km$h21) HRpeak (b$min21) U-14 (n = 21) PVT-CAR (km$h21) HRpeak (b$min21)
Mean difference (95% CI)
Reliability p
ES
Absolute CV%
Relative ICC (95% CI)
14.3 6 1.0 202.5 6 9.5
14.5 6 1.0 20.2 (20.33 to 0.01) 0.06 0.16 202.1 6 8.9 0.4 (21.79 to 2.61) 0.70 0.05
2.30 2.20
0.89 (0.79 to 0.94) 0.77 (0.58 to 0.88)
13.7 6 1.0 205.0 6 8.0
13.9 6 0.9 20.2 (20.42 to 0.02) 0.08 0.20 205.3 6 8.5 20.3 (24.75 to 4.13) 0.88 0.04
1.89 2.53
0.93 (0.78 to 0.98) 0.79 (0.42 to 0.93)
14.7 6 0.9 14.8 6 0.9 20.1 (20.39 to 0.12) 0.27 0.15 200.9 6 10.3 200.1 6 8.7 0.8 (21.75 to 3.47) 0.50 0.09
2.66 2.02
0.81 (0.58 to 0.92) 0.82 (0.61 to 0.92)
*CV = coefficient of variation; ICC = intraclass correlation coefficient; CI, confidence interval; PVT-CAR = peak velocity obtained from Carminatti’s test; HRpeak = peak heart rate.
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TABLE 3. Descriptive statistics (mean 6 SD) of anthropometric characteristics, maturity indicators, and physiological variables determined in the laboratory and field test for youth soccer players (study 2).* Total sample (43) Mean 6 SD Anthropometry Chronological age (y) Stature (cm) Sitting height (cm) Estimated leg length (cm) Body mass (kg) Fat free mass (kg) Fat mass (kg) Maturity indicators Maturity offset (y) Estimated age at PHV (y) ITT V_ O2peak (ml$kg21$min21) V_ O2peak (L$min21) vVT2 (km$h21) MAS (km$h21) PVITT (km$h21) HRpeak(ITT) (b$min21) Carminatti’s test PVT-CAR (km$h21) HRpeak(T-CAR) (b$min21)
14.0 167.5 86.8 80.7 56.7 49.1 7.5
6 6 6 6 6 6 6
0.9 10.4 5.7 5.8 10.0 8.5 2.4
13.2 160.7 83.0 77.7 49.6 42.9 6.7
0.4 6 1.1 13.7 6 0.5 60.2 3.40 13.8 15.8 16.0 199.6
6 6 6 6 6 6
U-14 (n = 20) Mean 6 SD 6 6 6 6 6 6 6
0.5 9.6 5.4 5.1 9.2 7.4 2.6
U-16 (n = 23) Mean 6 SD 14.7 173.5 90.0 83.5 62.6 54.4 8.3
20.6 6 0.9 13.8 6 0.6
5.2 0.66 1.3 1.4 1.4† 11.4
58.6 2.88 12.8 14.8 15.0 204.2
15.7 6 1.2 201.2 6 9.3
6 6 6 6 6 6
4.6 0.51 1.1 1.1 1.2 9.9
14.9 6 1.1 204.9 6 9.4
6 6 6 6 6 6 6
0.4 7.2 3.6 5.0 6.2 5.3 2.0
1.1 6 0.7 13.5 6 0.4 61.6 3.85 14.6 16.7 16.9 196.7
6 6 6 6 6 6
5.5 0.42 1.0 1.0 0.9† 10.7
16.4 6 0.8 197.6 6 7.9
_ O2peak = peak oxygen uptake; vVT2 = velocity related to second ventilatory threshold; *V MAS = maximal aerobic speed; PVITT = peak velocity determined in incremental treadmill test; HRpeak(ITT) = peak heart rate achieved in incremental treadmill test; PVT-CAR = peak velocity obtained from Carminatti’s test; HRpeak(T-CAR) = peak heart rate reached in Carminatti’s test. †p # 0.05; denotes a significant difference compared with the MAS and PVT-CAR for the total sample and U-16 group (within columns).
used to determine any significant difference between PVITT, MAS, and PVT-CAR. The Bonferroni post hoc test was used when necessary to identify differences. In the case of violation of the assumption of sphericity, the significance was established by using the Greenhouse-Geisser correction. Practical significance was assessed calculating Cohen’s d effect size (ES, 0.1 = trivial, 0.20 = small, 0.5 = medium, 0.8 = large) and partial eta squared (h2, 0.01 = small, 0.06 = medium, 0.14 = large) (13). Pearson’s product-moment correlations between the PVTCAR and laboratory aerobic fitness indicators were calculated first as zero order and then as partial correlations adjusting first for chronological age and maturity offset and then for estimated leg length and fat free mass. The magnitude of effects was qualitatively assessed according to Hopkins (22) as follows: trivial (r , 0.1), small (0.1 , r , 0.3), moderate (0.3 , r , 0.5), large (0.5 , r , 0.7), very large (0.7 , r , 0.9), nearly perfect (r . 0.9). The agreement of the measurements (MAS vs. PVT-CAR and HRpeak(ITT) vs. HRpeak(T-CAR)) was assessed with Bland and Altman plots with variables difference bias tested for
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significance against the null hypothesis (difference = 0). Heteroscedasticity was tested according to Ludbrook (29). Relative and absolute reliability were assessed using the intraclass correlation coefficient (ICC) and typical error of measurement expressed as coefficient of variation (CV%), respectively (23). Statistical significance was set at p # 0.05 for all analyses. The statistical power of total sample size calculated in this study was 0.99–1.00 (correlation analyses), 0.49–0.67 (Student’s t-test), and 0.99 (ANOVA with repeated measures). Calculations were performed with the statistical packages (SPSS 13.5 version; SPSS, Chicago, IL, USA) and GraphPad Prism (GraphPad Prism 5.0 Software Inc., San Diego, CA, USA).
RESULTS Reliability
The anthropometric and maturational characteristics of the young soccer players for the total sample and separately for the groups (U-12 and U-14) are represented in Table 1 (study 1). Table 2 shows the differences between the mean of the 2 test sessions (T1 and T2), ES, CV%, and ICCs of the PVT-CAR and HRpeak(T-CAR) obtained from the T-CAR for the total sample (pooled data) and separately by group (U-12 and U-14). There were no meaningful differences in the mean values of HRpeak(T-CAR) and PVT-CAR between T1 and T2 in either condition (pooled or separately by group). It is important to highlight that for total sample and U-12 group, although the p-value of the PVT-CAR was 0.06 and 0.08, respectively, the practical significance using ES suggests that the differences found at HRpeak(T-CAR) and PVT-CAR between T1 and T2 were trivial to small. Validity
Anthropometric, maturational characteristics, and physiological variables determined in the laboratory and field tests for the total sample and separately by groups (U-14 and U-16) are presented in Table 3 (study 2). In the U-14 group, there were no differences between the PVITT, MAS, and PVT-CAR (F = 0.991; p = 0.355; h2 = 0.05). Otherwise, for the total sample (F = 5.570; p = 0.013;
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sample and U-16, respectively). The HR values referring to TABLE 4. Bivariate and partial correlations of the peak velocity (PVT-CAR) with the incremental laboratory test variables of aerobic fitness, adjusting for CA and MO, and for ELL and FFM.* (HRpeak(ITT)) and T-CAR Partial correlation (HRpeak(T-CAR)) presented no significant difference for the Bivariate correlation CA, MO ELL, FFM total sample (t = 21.06; p = 0.30; ES = 0.15), U-14 (t = Total sample (n = 43) 0.46† 0.36† 0.45† PVT-CAR vs. V_ O2peak (ml$kg21$min21) 20.72; p = 0.48; ES = 0.07) 0.57z 0.31z 0.44† PVT-CAR vs. V_ O2peak (L$min21) and U-16 groups (t = 20.77; PVT-CAR vs. vVT2 0.69z 0.48z 0.59z p = 0.45; ES = 0.10), with PVT-CAR vs. MAS 0.81z 0.63z 0.68z a very large correlation (r = PVT-CAR vs. PVITT 0.86z 0.72z 0.78z 0.89, 0.90, and 0.86 for the total U-14 (n = 20) PVT-CAR vs. V_ O2peak (ml$kg21$min21) 0.48† 0.48† 0.74z sample, U-14 and U-16 groups, PVT-CAR vs. V_ O2peak (L$min21) 0.14 0.23 0.54† respectively; p , 0.01). PVT-CAR vs. vVT2 0.53† 0.53† 0.40 The correlations of PVT-CAR 0.75z 0.73z 0.73z PVT-CAR vs. MAS with the aerobic fitness variaPVT-CAR vs. PVITT 0.84z 0.82z 0.82z bles determined in the laboraU-16 (n = 23) PVT-CAR vs. V_ O2peak (ml$kg21$min21) 0.28 0.38 0.30 tory for the total sample and PVT-CAR vs. V_ O2peak (L$min21) 0.30 0.45 0.38 separately by group (U-14 PVT-CAR vs. vVT2 0.40 0.30 0.40 and U-16) are summarized in PVT-CAR vs. MAS 0.58z 0.62z 0.60z Table 4 (study 2). 0.60z 0.57z 0.61z PVT-CAR vs. PVITT The PVT-CAR was signifi*CA = chronological age; MO = maturity offset; ELL = estimated leg length; FFM = fat free cantly correlated with the mass; V_ O2peak = peak oxygen uptake; vVT2 = velocity related to second ventilatory threshold; and MAS for the total PV ITT MAS = maximal aerobic speed; PVITT = peak velocity determined in incremental treadmill test; sample and in both groups PVT-CAR = peak velocity obtained from Carminatti’s test. †p # 0.05. (U-14 and U-16). It was zp , 0.01. noticed that the PVT-CAR was significantly correlated to the vVT2 only for the total sample and the U-14 group. These correlation values did not change after adjustment for chroh2 = 0.12) and in U-16 group (F = 7.367; p = 0.005; h2 = nological age, biological maturity, and body size. The bivar0.25) differences were found. The results of pairwise comiate correlation between the PVT-CAR and V_ O2peak was only parisons showed values significantly higher for the PVITT meaningful for the total sample and U-14 group. When the compared with the MAS (p = 0.001 and p = 0.013; total body size descriptors were controlled, the correlation values sample and U-16 group, respectively) and PVT-CAR (p = increased for the relative V_ O2peak (r = 0.74) and absolute 0.015 and p = 0.005; total sample and U-16 group, respecV_ O2peak (r = 0.54) in the U-14 group, while remaining tively). However, no differences were observed between the unchanged for the total sample. Specifically in the U-16 MAS and the PVT-CAR (p = 1.000 and p = 0.459, for the total
Figure 1. Scatter plot of PVITT (km$h21) and PVT-CAR (km$h21) for total sample, U-14 and U-16 groups. SEE = standard error of estimate.
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Aerobic Fitness Assessment in Youth Soccer
Figure 2. Bland-Altman plot of MAS vs. PVT-CAR (upper panels) and HRpeak(ITT) vs. HRpeak(T-CAR) (lower panels). Dotted lines represent the bias and solid lines denote lower and upper 95% limits of agreement.
group, this relationship was observed only between the PVT-CAR and the relative V_ O2peak (r = 0.45) after adjusting for chronological age and maturity offset (Table 4). Relationship between PVT-CAR and PVITT for the total sample, U-14 and U-16 groups, predictive equation, coefficient of determination (R2), and standard error of estimate are illustrated in Figure 1. Linear relationship was observed between PVT-CAR and PVITT in each condition (i.e., pooled data or separately by group). Additionally, Figure 2 shows the bias 695% limits of agreement for the comparison between the MAS and PVT-CAR (0.08 6 1.62, 20.12 6 1.56, and 0.26 6 1.63 km.hour21) and the HRpeak(ITT) and HRpeak(T-CAR) (20.24 6 8.64, 20.70 6 8.60, and 0.19 6 8.84 b$min21) for the total sample, U-14 and U-16 groups, respectively. It should be noted that there was no systematic error (heteroscedasticity) for agreement measures between the physiological variables determined in the laboratory and field tests.
DISCUSSION The primary aim of this investigation was to assess the reliability and concurrent validity of PVT-CAR in young soccer players classified as U-12, U-14, and U-16. The results of the current study showed that PVT-CAR may be considered as a predictor of MAS. Indeed, the PVT-CAR was largely to very largely correlated with PVITT, MAS, V_ O2peak, and vVT2. Furthermore, PVT-CAR and HRpeak(T-CAR) showed a good relative and absolute reliability in both competitive age groups analyzed (U-12 and U-14). These findings
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provide evidence that T-CAR may be considered as an appropriate test for the assessment of aerobic fitness under field conditions in young soccer players of different competitive age groups. Short-term relative and absolute reliability are relevant measures of test applicability (14). Clinical studies suggested that tests providing CV% and ICC values lower than 10% and higher than 0.75 respectively, should be considered as able to determine practical acceptance of clinical variations (17). In this study, the ICC (0.81–0.93, good to excellent) and CV% (1.9–2.7%) values for PVT-CAR in both groups (U-12 and U-14) showed that the T-CAR was a reliable test in the specific experimental set-up considered. Additionally, the low CV% values suggest relatively small within-subject variation between trials. Familiarization with the testing protocol may have contributed to the high reliability of PVT-CAR. The reported CV% for PVT-CAR was slightly lower than that reported for performance in the Yo-Yo IR1 (3.8%) and MSFT (3.6%) in 18 young Italian soccer players (16). Similarly, the reliability values in this investigation were consistent with those reported for T-CAR short-term repeated measure design in male junior competitive match level soccer players whose ICC and CV% were 0.94 (good to excellent) and 1.3%, respectively (19). These results strongly demonstrate that T-CAR requires only a small familiarization to provide reliable data. Another important finding of this study was the good HRpeak(T-CAR) reliability (ICC = 0.79 and 0.83, CV = 2.5 and 2.0%; for the U-12 and U-14 groups, respectively) obtained
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Journal of Strength and Conditioning Research from T-CAR in young soccer players. Similar values of relative and absolute reliability were obtained when the data were pooled (total sample; Table 2). Additionally, the HRpeak found in the ITT and the HRpeak obtained in T-CAR were shown to be very largely associated (r = 0.90 and 0.86, for the U-14 and U-16 groups, respectively; p , 0.001) and not significantly different (p . 0.05; Table 3) within each group (U-14 and U-16). Interestingly, the interpretation of 695% limits of agreement constructed from the analysis of these 2 measures (HRpeak(T-CAR) vs. HRpeak(ITT); lower panels; Figure 2) suggests that if the HRpeak(ITT) were to be estimated from HRpeak reached during the T-CAR for a single participant a variation of up to 69 b$min21 or 64.2% could be visualized. This individual variation in the HRpeak(T-CAR) of youth soccer players has practical relevance to coaches because it can be used to estimate the HRpeak(ITT), and therefore be used to control the internal training load and identify the target zones (i.e., ;90% HRpeak) of generic aerobic training (interval training) and specific training (i.e., small sided games) for the development of aerobic fitness (5). The concurrent validity of the T-CAR was performed examining the association (i.e., correlation) of PVT-CAR with PVITT, MAS, V_ O2peak, and vVT2 (i.e., criterion measurement) achieved during a standard treadmill test and comparing PVT-CAR with MAS (i.e., reference variable), characterized in this study as the MAS achieved during the treadmill test (3). Relative mean values for V_ O2peak show that players from both groups (U-14 and U-16) had a high degree of aerobic fitness, particularly when compared with values reported for males of similar ages in the general population (30). Significant differences between PVT-CAR and MAS in the U-14 (14.9 6 1.1 vs. 14.8 6 1.1 km$h21, p = 1.00) and U-16 groups (16.4 6 0.8 vs. 16.7 6 1.0 km$h21, p = 0.46) were not found. It should be noted that the same results were obtained when the data were pooled (total sample). However, the average values of PVT-CAR and PVITT presented significant differences in the U-16 group and total sample (for more details see Table 3). Similar findings have been reported showing that the peak velocity determined in treadmill tests is higher than that reached in field tests, specifically due to the constant direction changes, which contribute to a reduced running economy (4,19,21). Moreover, previous studies using the MSFT and Yo-Yo IR1 have found that the peak velocity obtained with fixed distance protocols in youth soccer and basketball players also underestimates the MAS (vV_ O2max) (15,40), which is different to the present findings. In this perspective, the additional contribution of T-CAR compared with other protocols is the ability to estimate and/or predict the velocity that corresponds to maximal aerobic power (i.e., MAS) in well-trained young soccer players (i.e., V_ O2peak $60.2 ml$kg21$min21) under field conditions (test applicability). It could be speculated that the higher peak velocity obtainable in T-CAR compared
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to other field tests is probably due to a combination of two factors (19). First, the higher peak velocity reached in T-CAR could be related to the work rest ratio considered. Second, the considered distance increment at each stage, which enables greater distances (;25–27 m) to be covered by players during the final test stages, compared with other tests (20 m), may reduce the time spent accelerating and decelerating after each turn. This test characteristic would reduce the occurrence of neuromuscular fatigue. Moreover, the higher energetic cost of running over shorter distances (i.e., 20 m) (6), could also explain the higher values of peak velocity during T-CAR. Furthermore, it was observed that for both groups (U-14 and U-16), the PVT-CAR was significantly correlated to the PVITT, MAS, and V_ O2peak (aerobic power indices). However, the association between the PVT-CAR and vVT2 (aerobic capacity index) was observed only in the U-14 group (Table 4). Interestingly, these relationships tended to remain unchanged for most analyses after control for the influence of age, biological maturity, and body size, suggesting that the relationship between the PVT-CAR and the physiological indices of aerobic fitness does not seem to be affected by growing or biological maturity. However, the relationship between PVT-CAR and V_ O2peak increased significantly in the U-14 group after adjusting for estimated leg length and fat free mass (Table 4), showing that this relationship seems to be dependent on body size descriptors in young soccer players around the PHV (Table 3). As a complementary result, the agreement analysis between MAS and PVT-CAR was performed using the Bland and Altman plots (Figure 2). This information is of critical importance for coaches who want to use field tests to monitor changes in young players’ fitness and guide training prescription. This statistical method has been widely used in the sports science area to evaluate the performance measures relevant to different sports (1,13). It should be noted that, in this study, the bias and limits of agreement between MAS and PVT-CAR (upper panels; Figure 2) for the total sample (0.08 6 1.62 km$h21) or separately for the U-14 (20.12 6 1.56 km$h21) and U-16 groups (0.26 6 1.63 km$h21) were similar to the peak velocity values found in the 45-15 test (20.20 6 1.7 km$h21) in Italian youth soccer players (25). To the best of our knowledge, this is the first study to show the intraindividual variation in the estimative of MAS from PVT-CAR in youth soccer players from different competitive categories (U-14 and U-16). Although there can be multiple sources of error when measurements are made in the sport and exercise sciences (1), a possible explanation for the variations found in this study can be attributed to the specific characteristics (intermittent vs. continuous) of each protocol in which the PVT-CAR and MAS were determined. In this sense, the limits of agreement in PVT-CAR for both groups (U-14 and U-16) have an acceptable practical significance for predicting MAS, however, should be used with caution to individualize the VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Aerobic Fitness Assessment in Youth Soccer training intensities, making adjustments in PVT-CAR to correct these variations inherent in the protocol. Therefore, T-CAR seems to be an interesting test of practical relevance to assess aerobic fitness and to prescribe generic (PVT-CAR) and specific (individual HRpeak) training in young soccer players during adolescence, since longitudinal studies have shown that the highest gain in aerobic fitness occurs, on average, close to the PHV age (32). However, further studies are needed to examine the effect of using the PVT-CAR (high-intensity intermittent running) as a training tool for the aerobic fitness of young soccer players. Moreover, future investigations examining the influence of growth and maturation on the performance in T-CAR of young soccer players are required.
PRACTICAL APPLICATIONS Carminatti’s test (T-CAR) can be considered a valid field test to estimate the MAS based on the PVT-CAR, and also to estimate the HRpeak of young soccer players. These findings enable coaches to monitor and evaluate the development of the aerobic performance of young soccer players during adolescence. The good reliability and validity of the HRpeak(T-CAR) found in this study enables the use of this indirect measure as an important parameter to control the internal training load during functional and generic training sessions designed to develop aerobic fitness in youth soccer players. Additionally, the PVT-CAR can be used by coaches in the prescription of high-intensity intermittent training models in children and adolescents simultaneously using the same audio cue, as well as to monitor performance improvements induced during the competitive season, given the high reliability of PVTCAR. Therefore, these results should be of interest to coaches, sport scientists, and others involved in the selection and development of youth soccer players.
ACKNOWLEDGMENTS We gratefully appreciate the patience and cooperation of the young athletes, coaches, and parents during the execution of this study and the National Council of Technological and Scientific Development (CNPq/Brazil) for financial support.
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