SPECIFIC DETERMINATION OF MAXIMAL LACTATE STEADY STATE IN SOCCER PLAYERS JOA˜O P. LOURES,1 KARIM CHAMARI,2 ELIEL C. FERREIRA,3 EDUARDO Z. CAMPOS,1 ALESSANDRO M. ZAGATTO,4 FABIO MILIONI,1 ADELINO S.R. DA SILVA,5 AND MARCELO PAPOTI5 1
Post-Graduation Program in Motricity Science, Sa˜o Paulo State University, Rio Claro, Sa˜o Paulo, Brazil; 2Athlete Health and Performance Research Center, Aspetar, Qatar; 3Laboratory of Exercise Physiology (LAFE), Sa˜o Paulo State University, Presidente Prudente, Sa˜o Paulo, Brazil; 4Physical Education Department, Sa˜o Paulo State University, Bauru, Sa˜o Paulo, Brazil; and 5School of Physical Education and Sports of Ribeira˜o Preto, Sa˜o Paulo University, Ribeira˜o Preto, Sa˜o Paulo, Brazil ABSTRACT
Loures, JP, Chamari, K, Ferreira, EC, Campos, EZ, Zagatto, AM, Milioni, F, da Silva, ASR, and Papoti, M. Specific determination of maximal lactate steady state in soccer players. J Strength Cond Res 29(1): 101–106, 2015—The aim of this study was to establish the validity of the anaerobic threshold (AT) determined on the soccer-specific Hoff circuit (ATHoff) to predict the maximal lactate steady-state exercise intensity (MLSSHoff) with the ball. Sixteen soccer players (age: 16.0 6 0.5 years; body mass: 63.7 6 9.0 kg; and height: 169.4 6 5.3 cm) were submitted to 5 progressive efforts (7.0–11.0 km$h21) with ball dribbling. Thereafter, 11 players were submitted to 3 efforts of 30 minutes at 100, 105, and 110% of ATHoff. The ATHoff corresponded to the speed relative to 3.5 mmol$L21 lactate concentration. The speed relative to 4.0 mmol$L21 was assumed to be ATHoff4.0, and the ATHoffBI was determined through bisegmented adjustment. For comparisons, Student’s t-test, intraclass correlation coefficient (ICC), and Bland and Altman analyses were used. For reproducibility, ICC, typical error, and coefficient of variation were used. No significant difference was found between AT test and retest determined using different methods. A positive correlation was observed between ATHoff and ATHoff4.0. The MLSSHoff (10.6 6 1.3 km$h21) was significantly different compared with ATHoff (10.2 6 1.2 km$h21) and ATHoffBI (9.5 6 0.4 km$h21) but did not show any difference from LAnHoff4.0 (10.7 6 1.4 km$h21). The MLSSHoff presented high ICCs with ATHoff and ATHoff4.0 (ICC = 0.94; and ICC = 0.89; p # 0.05, respectively), without significant correlation with ATHoffBI. The results suggest that AT determined on the Hoff circuit is reproducible and capable of predicting MLSS. The ATHoff4.0 was the method that presented a better approximation to MLSS. Therefore, it is possible to assess submaximal
Address correspondence to Marcelo Papoti, [email protected]. 29(1)/101–106 Journal of Strength and Conditioning Research Ó 2015 National Strength and Conditioning Association
physiological variables through a specific circuit performed with the ball in young soccer players.
KEY WORDS anaerobic threshold, blood lactate equilibrium, specificity, validation
INTRODUCTION
A
erobic fitness has great importance to soccer player performance (8,23). A well-developed aerobic system decreases the recovery time after high-intensity efforts and is therefore of paramount importance for sports composed of repeated intense efforts as soccer (24). A developed aerobic system also increases the number of sprints and the distance covered during a match (13), improves technical performance, and promotes more ball involvement during the game (13,19). Therefore, the aerobic capacity evaluation is essential for performance optimization (19). The gold standard protocol to evaluate aerobic capacity is the maximal lactate steady state (MLSS) that represents the highest exercise intensity in which lactate production and clearance are equilibrated (1,2). However, because of the requirement for individuals to complete 4–6 constant-load exercise bouts on separate days to measure MLSS, the anaerobic threshold (AT) can be used to predict MLSS (9,12). Generally, the AT determination employs continuous running on a treadmill ergometer, which is highly reproducible and valid. However, this type of protocol is not attractive to the players (14) and is limited because there is a lack of specificity of the motor pattern compared with those used during training and match. Hoff et al. (14) have proposed a soccer-specific aerobic endurance training in a circuit with jumps, running backwards, and direction changes, all carried out with the soccer ball, which approximates the reality of the game. The Hoff circuit seems attractive for soccer players and has then been presented as a valid test for determining soccer players’ endurance performance (6). Indeed, the performance to dribbling the ball on the circuit as modified by VOLUME 29 | NUMBER 1 | JANUARY 2015 |
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Specific Aerobic Test in Soccer Players Chamari et al. (6) is correlated to the players’ maximal oxygen uptake. Recently, Zouhal et al. (26) have used the Hoff circuit with dribbling ball as a specific aerobic exercise; however, the exercise prescription on Hoff circuit is performed using heart rate (HR) (26) or with maximal effort (20). To our knowledge, no study has been carried out to evaluate whether it is possible to detect AT on the Hoff circuit with ball control/dribbling. In addition, the reliability and validity of AT determination on the Hoff circuit were not performed. If this is possible (i.e., reliability and valid), this would be a specific protocol for AT evaluation, training prescription, and determination of alterations soccer players’ physical fitness. Furthermore, because of the methodology limitation of MLSS assessment (i.e., high time required), the investigation of reproducibility and validity of the AT determined on the Hoff circuit through a unique incremental test would be very interesting for training practical purposes. In addition, between the AT methodologies, the speed corresponded to 3.5, 4.0 mmol$L21 and the intersection of 2 linear regressions (bisegmented method) have been used (9,12,18). These methods have already been validated to predict the MLSS during continuous running tests (9,12). Thus, the aim of this study was to test the reproducibility of these 3 methods of AT determination assessed on the Hoff circuit and to verify whether these AT methods can predict MLSS. We hypothesized that it is possible to determine the AT on the Hoff circuit using these 3 methods, and these methods are reliable and valid to predict MLSS of soccer players.
METHODS Experimental Approach to the Problem
To test the hypothesis that is possible to determine the AT on the Hoff circuit and that the AT is reliable and valid to
predict the MLSS, the present research was designed as an experimental cross-sectional study. This study was divided in 2 parts. In the first part of the study, our purpose was to determine the AT on the Hoff circuit and its reliability. In the second part of the study, we aimed to analyze the validity of AT for predicting MLSS intensity measured on the Hoff circuit. In the second part of the study 2, the MLSS was set as dependent variable, whereas AT on the Hoff circuit as independent variable. Primarily, the subjects were familiarized with the Hoff circuit. Then, they performed 5 progressive efforts on the Hoff circuit (6) to determine AT. The athletes completed 2 laps (580 m) at each speed, with an increment of 1 km$h21 per 2 laps. The AT on the Hoff circuit was determined through 3 different techniques (i.e., the speed corresponding to the 3.5 and 4.0 mmol$L21 and using the bisegmented method). The same protocol was repeated after 48 hours to verify its reproducibility. After these procedures, on separate days, the athletes performed random efforts of 100, 105, and 110% of ATHoff intensity for 30 minutes to detect the MLSS on the Hoff circuit (MLSSHoff ). Subjects
The sample size was calculated based on the assumption that AT is reliable and presents strong correlations with MLSS (r . 0.90). We used G*Power 3.1 software (Du¨sseldorf, Germany) to determine that a sample size of 10 subjects was the minimum needed to provide a statistical power of 90% with an alpha of 0.05 for the analysis. Therefore, a group of 16 soccer players (age = 16.0 6 1.0 years; body mass = 63.7 6 9.0 kg; lean mass = 52.4 6 6.1 kg; height = 169.4 6 5.3 cm; and fat percentage = 13.4 6 4.6%) took part in study 1 and a subgroup of 11 soccer players in study 2 (age = 15.8 6 0.6 years; body mass = 63.1 6 9.9 kg; lean mass = 52.0 6 7.0 kg; height = 169.0 6 6.3 cm;
TABLE 1. Comparison, coefficient of variation, effect size, and typical error in the values of anaerobic threshold determined by a fixed concentration of 3.5 mmol$L21 (ATHoff) and 4.0 mmol$L21 (ATHoff4,0), and through the bisegmented method (ATHoffBI).*† CV (%)
Test 10.0 6 0.8 (9.6–10.4) ATHoff (km$h21) HRAT-Hoff (b$min21) 195.2 6 19.0 (182.0–201.1) 10.7 6 0.7 (10.0–10.7) ATHoff4.0 (km$h21) HRAT-Hoff4.0 191.6 6 18.2 (185.1–205.3) (b$min21) 9.2 6 0.6 (8.5–10.0) ATHoffBI (km$h21) HRAT-HoffBI 181.0 6 13.4 (173.9–188.2) (b$min21)
Retest
7.94 10.2 6 1.1 9.35 192.5 6 18.7 7.14 10.7 6 1.2 9.73 188.0 6 17.9
(9.6–10.7) (178.1–198.5) (9.9–11.0) (182.1–203.1)
Effect size
CV (%)
0.218 10.80 0.225 9.58 0.2938 11.68 0.155 9.75
6.67 9.4 6 0.4 (9.1–9.6) 0.034 7.47 175.3 6 15.4 (167.9–185.2) 0.391
4.60 8.81
Typical error 0.44 11.93 0.57 13.33 0.47 8.01
*The values of HR of each intensity are reported (n = 16). The values are given as mean 6 SD (95% confidence interval). †ATHoff = anaerobic threshold determined by a fixed concentration of 3.5 mmol$L21; HRAT-Hoff = heart rate corresponding to ATHoff;
ATHoff4.0 = anaerobic threshold determined by a fixed concentration of 4.0 mmol$L21; HRAT-Hoff4.0 = heart rate corresponding to ATHoff4.0; ATHoffBI = anaerobic threshold determined by a bisegmented method; HRAT-HoffBI = heart rate corresponding to ATHoffBI.
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Figure 1. Mean 6 SD values and comparisons between MLSSHoff and ATHoff (A), MLSSHoff and ATHoff4.0 (B), and MLSSHoff and ATHoffBI (C). *p , 0.05 to MLSSHoff.
and fat percentage = 13.1 6 5.0%). They played in amateur competitions (competition experience at least 3 years, 3–4 training per week, 1.5–2 hours per training session) and voluntarily participated in this study. Body composition data were estimated using the DEXA scan (GE Lunar–DPX-NT; General Electric, Fairfield, CT, USA) (10,11). The informed consent was obtained from a legal representative for each of the subjects signed before their participation in the study. The experimental protocol was approved by the Research Ethics Committee of the Sao Paulo State University (Protocol No. 54/2010, Sao Paulo State University, Faculty of Sciences and Technology of Presidente Prudente) and was designed in accordance with the ethical standards of the Helsinki declaration. Determination of Anaerobic Threshold on the Hoff Circuit (ATHoff)
Before the experimental procedures, the subjects were instructed to maintain the habitual food intake and sleep behavior. In addition, during the tests, water was provided when requested. All tests procedures occurred in the afternoon, during training sessions, between July and September (competitive period). Before ATHoff determination, the subjects performed a familiarization trial on the Hoff circuit. Initially, without ball, the soccer players just ran at different speeds. Then, with the ball, the subjects dribbled through the circuit in different speeds controlled by sound stimulus. In a subsequent day, the players underwent 5 progressive efforts of 580 m (2 laps) on the Hoff circuit (6). The initial speed was
7.0 km$h21, and on each 2 successive laps, the speed was incremented to 1 km$h21 reaching 11 km$h21 for the last 2 laps. The speed was controlled by sonorous stimuli every 58 m. After each 2 laps at the same speed (i.e., 580 m), blood samples were collected (25 ml) from the earlobe to determine blood lactate concentration ([La2]). The HR was measured continuously using an HR monitor (Forerunner 410; Garmin, Olathe, KS, USA) and using a recording frequency of the data each 4 seconds. The [La2] was plotted vs. speed steps, and then were adjusted exponentially. The speed corresponding to the lactate concentration of 3.5 mmol$L21 was assumed as ATHoff, and the speed equivalent to 4.0 mmol$L21 was assumed as ATHoff4.0 (12). The AT was also determined using the bisegmented method as described by Matsumoto et al. (18). From these values, and the linear relation between speed and HR, the HR corresponding to the AT intensities was determined (HRAT-Hoff, HRAT-Hoff4.0, HRAT-HoffBI). The entire test was again performed after 48 hours to determine the reproducibility of these methods. Determination of the Maximal Lactate Steady-State Intensity on the Hoff Circuit
For MLSSHoff determination, the players were submitted to 3 random efforts of 30 minutes with speeds corresponding to 100, 105, and 110% of ATHoff. The choice of the 100% intensity of ATHoff instead of lower intensities was made because stabilization of blood lactate at 95% of ATHoff had been previously observed in a pilot study (M. Papoti, personal data). VOLUME 29 | NUMBER 1 | JANUARY 2015 |
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Specific Aerobic Test in Soccer Players These efforts were performed with the ball on the Hoff circuit (6) and were separated by a minimum of 24 hours and a maximum of 72 hours. Before the efforts and every 5 minutes subsequent to the efforts, a blood sample was collected as described above for [La2] determination. The MLSSHoff was assumed to be the intensity where [La2] presented a variation of no more than 1 mmol$L-1during the last 20 minutes of the effort (1). Blood Analysis
Twenty five microliters of blood was collected from the subjects’ earlobes and was deposited in 1.5-ml polyethylene tubes (Eppendorf, Sa˜o Paulo, SP, Brazil) containing 50 ml of 1% sodium fluoride. After this, 25 ml of the homogenized solution was added to an electrochemical lactate analyzer (1500 Sport model; Yellow Spring Instruments, Yellow Springs, OH, USA) (4).The electrochemical lactate analyzer was calibrated after every 5 blood samples analyzed using a 5.0 and 15 mmol$L21 lactate standard solution according to the manufacturer’s instruction. Blood lactate concentrations were expressed in millimoles per liter. Statistical Analyses
The data are expressed as mean 6 SD and 95% confidence interval (95% CI). The normality and homogeneity of the data were confirmed with the Shapiro-Wilk’s and Levene’s tests, respectively. To verify the reliability of the different methods of AT measures, the comparison between test
and retest values was analyzed using the paired Student’s t-test, intraclass correlation (ICC) test, typical error, and coefficient of variation (CV). To verify the differences and the agreement of the AT intensities to MLSSHoff and thereby to confirm the validity, we used the Bland and Altman analyses (3), Student’s t-test, and ICC test. The effect sizes (ESs) obtained in each statistical analysis were also presented and interpreted as proposed by Hopkins (www.sportsci.org/ resource/stats), with ES ,0.2 considered as trivial, small between 0.2 and 0.5, moderate between 0.6 and 1.1, large between 1.2 and 1.9, and very large .2.0. The significance level was fixed to be 5% (p # 0.05).
RESULTS The AT values determined through the 3 methods are described in Table 1. No significant difference (p . 0.05) was found between test and retest values of ATHoff, ATHoff4.0, and ATHoffBI, as well as between HR associated with the AT speed. In addition, the effect sizes for these comparisons were considered between trivial and small. Significant correlations were found between test and retest values for ATHoff (ICC = 0.79; p # 0.05) and ATHoff4.0 (ICC = 0.69; p # 0.05); however, ATHoffBI did not present a significant correlation. There was a significant intraclass correlation between test and retest for HRAT-HoffBI (ICC = 0.70; p # 0.05) and HRAT-Hoff (ICC = 0.56; p # 0.05). The typical error for AT determined through the 3 methods
Figure 2. Average of systematic error, upper and lower limits of the agreements obtained by Bland and Altman (3) and between MLSSHoff and ATHoff (A), MLSSHoff and ATHoff4.0 (B), and MLSSHoff and ATHoffBI (C).
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Journal of Strength and Conditioning Research varied between 0.44 and 0.57 km$h21, and the HR relative to the AT presented a typical error between 8.01 and 13.33 b$min21. The MLSSHoff corresponded to 10.6 6 1.3 km$h21 (95% CI = 9.5–11.3 km$h21) and was not statistically different from ATHoff4.0 (95% CI = 9.6–11.1.3 km$h21; ES = 0.067, trivial); however, it was higher than ATHoffBI (95% CI = 9.2– 9.7 km$h21; ES = 1.027, moderate) and ATHoff (95% CI = 9.2–10.8 km$h21; ES = 0.298, moderate), the latter of which underestimated MLSSHoff by only 3.4%. These values are shown in Figure 1. Besides this, MLSSHoff showed a high ICC with both ATHoff (ICC = 0.94; p # 0.05) and ATHoff4.0 (ICC = 0.80; p # 0.05), whereas ATHoffBI did not present any significant correlation with MLSSHoff. The Bland and Altman analysis revealed good agreement between MLSSHoff, ATHoff, and ATHoff4.0 (Figures 2A, B, respectively), as the bias was close to zero, and the agreement limits demonstrated that the difference between the 2 measurements was of only 1.33 km$h21.
DISCUSSION The aims of this study were to determine the reproducibility of the AT determined on the soccer-specific Hoff circuit (6) using 3 different methods and to verify whether this AT could predict the MLSS. The main findings were (a) the AT determined on the Hoff circuit was reproducible because no difference was found between test and retest for any method of AT determination, a trivial to small effect size on differences and the typical error of the 3 methods of determination were very small; (b) the ATHoff4.0 did not present difference and was strongly correlated with MLSSHoff, and ATHoff underestimated the MLSSHoff speed by only 3.4% and was significantly correlated with it. These results confirm partially our initial hypotheses because only the ATHoff4.0 was considered valid to predict MLSS. The AT determined through the 3 methods on the Hoff circuit were reliable. Only ATHoffBI did not present correlation between test and retest; however, the within-subject variation of the AT was within 0.57 km$h21, which suggests that, independent of the method of determination, the speed is very reproducible and could be used for the assessment. Williams et al. (25) also studied the reliability of a field test to evaluate the aerobic fitness of university soccer players. However, the only analyzed variable was the time to perform 4 laps on the field circuit. On the robust study of Krustrup et al. (17), they verified that the Yo-Yo intermittent recovery test (level 1) is reliable and can be used as a precise measure of physiological performance in soccer players. Williams et al. (25) observed a higher ICC than this study (r = 0.98 vs. r = 0.79, respectively), whereas the correlation coefficient of Krustrup et al. (17) was 0.98. However, these studies did not report the typical error and, as proposed by Hopkins (15), the typical error is the best way to analyze within-subjects’ variation. This study verified a variation between 0.44 and 0.57 km$h21, and this would be of poten-
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tial value for training prescription and/or detecting training effects because a variation of above 0.57 and below 0.44 km$h21 might indicate an improvement or decrease in physical fitness, respectively (22). In the context of aerobic fitness in soccer players, the determination of AT is essential. Helgerud et al. (13) showed that if the AT increases, then the ball involvement and number of sprints also improve. As observed on the AT, the HR corresponding to the AT of the 3 methods of determination did not present any statistical difference. The HRAT-HoffBI and HRAT-Hoff presented moderate and low significant ICC values, respectively, whereas the HRAT-Hoff4.0 did not present correlation. However, together with the relatively small typical error shown in the study, the small CV indicates that the AT HR is reliable. Thus, the HR corresponding to the AT can be used as a reliable tool for controlling and prescription of training, especially it usually does not change during a season, even with an increase in aerobic fitness (5,19). This study did not display differences between ATHoff4.0 and MLSSHoff. ATHoff and ATHoff4.0 had significant correlation with MLSSHoff (ICC = 0.94 and 0.89; p # 0.05, respectively). To our knowledge, this is the first study to validate the AT evaluation on the Hoff circuit. Besides the absence of differences and the high ICC values, only ATHoff4.0 presented a relatively good agreement limit and small bias (20.37) with MLSSHoff. These findings indicate that ATHoff4.0 is an interesting and simple method for estimating MLSSHoff. It is worth noting that ATHoff underestimated MLSSHoff by only 3.4% and presented very high ICCs of 0.94 (p # 0.05). To our knowledge, this is the first study to validate a specific soccer AT test to predict MLSS. This result can increase the use of this specific test to evaluate soccer players’ aerobic capacity and the use of this intensity for training prescription. However, the sensibility of these methods for AT evaluation still needs to be investigated in future studies. The ATHoff underestimates the MLSS by only 3.4%, whereas the ATHoff4.0 was not different from the MLSS. Usually, the AT corresponded to the fixed [La2] of 4.0 mmol$L21 is attained on incremental tests with stages during around 5 minutes (12). Jones and Doust (16) did not find any difference between MLSS and AT in runners using a fixed [La2] of 3.5 mmol$L21 and stages during 3 minutes. Contrary, this study used a stage length of z5 minutes, and the AT with a fixed [La2] of 4.0 mmol$L21 was not different from the MLSS. The hypothesis for this result is that Sassi et al. (21) verified that the energetic cost increases when the subjects are evaluated on an absorptive surface (grass). Because the cost is higher, the [La2] for the same intensity would be higher (7). Thus, when evaluating AT specifically, independent of the effort stage length (12), the fixed concentration of 4.0 mmol$L21 should be used. To conclude, the AT determined on the Hoff circuit through 3 different methods is highly reproducible, as well as the HR relative to AT. Considering the good agreement between ATHoff and ATHoff4.0 and MLSSHoff, this test can be VOLUME 29 | NUMBER 1 | JANUARY 2015 |
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Specific Aerobic Test in Soccer Players used to predict MLSS in young soccer players, with the latter showing the best accuracy.
PRACTICAL APPLICATIONS This study provided a new method to determine the AT of soccer players, which is useful because it considers the common direction changes performed by soccer players during a match and the technical demands of the game. In addition, this method is more attractive for athletes because of the involvement with the soccer ball. In summary, the use of this aerobic capacity determination method may increase the adherence of the soccer players and be closer to the game reality, providing a more reliable index for training prescription. Anaerobic threshold determination on the Hoff circuit has wide applications for coaches and fitness coaches and could be used for the following: Training prescription: The ATHoff or ATHoff4.0 could be used to prescribe continuous endurance training or interval training with higher. The HR relative to the AT could be used to control training on the Hoff circuit or possibly in small-sided games because both are performed on grass and need ball control. Monitoring the effects of training: Due to the small typical error (z0.44 km$h21; Table 1), any increase in AT wide above or under this value should be accepted as a significant alteration of endurance fitness.
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Post-Graduation Program in Motricity Science, Sa˜o Paulo State University, Rio Claro, Sa˜o Paulo, Brazil; 2Athlete Health and Performance Research Center, Aspetar, Qatar; 3Laboratory of Exercise Physiology (LAFE), Sa˜o Paulo State University, Presidente Prudente, Sa˜o Paulo, Brazil; 4Physical Education Department, Sa˜o Paulo State University, Bauru, Sa˜o Paulo, Brazil; and 5School of Physical Education and Sports of Ribeira˜o Preto, Sa˜o Paulo University, Ribeira˜o Preto, Sa˜o Paulo, Brazil ABSTRACT
Loures, JP, Chamari, K, Ferreira, EC, Campos, EZ, Zagatto, AM, Milioni, F, da Silva, ASR, and Papoti, M. Specific determination of maximal lactate steady state in soccer players. J Strength Cond Res 29(1): 101–106, 2015—The aim of this study was to establish the validity of the anaerobic threshold (AT) determined on the soccer-specific Hoff circuit (ATHoff) to predict the maximal lactate steady-state exercise intensity (MLSSHoff) with the ball. Sixteen soccer players (age: 16.0 6 0.5 years; body mass: 63.7 6 9.0 kg; and height: 169.4 6 5.3 cm) were submitted to 5 progressive efforts (7.0–11.0 km$h21) with ball dribbling. Thereafter, 11 players were submitted to 3 efforts of 30 minutes at 100, 105, and 110% of ATHoff. The ATHoff corresponded to the speed relative to 3.5 mmol$L21 lactate concentration. The speed relative to 4.0 mmol$L21 was assumed to be ATHoff4.0, and the ATHoffBI was determined through bisegmented adjustment. For comparisons, Student’s t-test, intraclass correlation coefficient (ICC), and Bland and Altman analyses were used. For reproducibility, ICC, typical error, and coefficient of variation were used. No significant difference was found between AT test and retest determined using different methods. A positive correlation was observed between ATHoff and ATHoff4.0. The MLSSHoff (10.6 6 1.3 km$h21) was significantly different compared with ATHoff (10.2 6 1.2 km$h21) and ATHoffBI (9.5 6 0.4 km$h21) but did not show any difference from LAnHoff4.0 (10.7 6 1.4 km$h21). The MLSSHoff presented high ICCs with ATHoff and ATHoff4.0 (ICC = 0.94; and ICC = 0.89; p # 0.05, respectively), without significant correlation with ATHoffBI. The results suggest that AT determined on the Hoff circuit is reproducible and capable of predicting MLSS. The ATHoff4.0 was the method that presented a better approximation to MLSS. Therefore, it is possible to assess submaximal
Address correspondence to Marcelo Papoti, [email protected]. 29(1)/101–106 Journal of Strength and Conditioning Research Ó 2015 National Strength and Conditioning Association
physiological variables through a specific circuit performed with the ball in young soccer players.
KEY WORDS anaerobic threshold, blood lactate equilibrium, specificity, validation
INTRODUCTION
A
erobic fitness has great importance to soccer player performance (8,23). A well-developed aerobic system decreases the recovery time after high-intensity efforts and is therefore of paramount importance for sports composed of repeated intense efforts as soccer (24). A developed aerobic system also increases the number of sprints and the distance covered during a match (13), improves technical performance, and promotes more ball involvement during the game (13,19). Therefore, the aerobic capacity evaluation is essential for performance optimization (19). The gold standard protocol to evaluate aerobic capacity is the maximal lactate steady state (MLSS) that represents the highest exercise intensity in which lactate production and clearance are equilibrated (1,2). However, because of the requirement for individuals to complete 4–6 constant-load exercise bouts on separate days to measure MLSS, the anaerobic threshold (AT) can be used to predict MLSS (9,12). Generally, the AT determination employs continuous running on a treadmill ergometer, which is highly reproducible and valid. However, this type of protocol is not attractive to the players (14) and is limited because there is a lack of specificity of the motor pattern compared with those used during training and match. Hoff et al. (14) have proposed a soccer-specific aerobic endurance training in a circuit with jumps, running backwards, and direction changes, all carried out with the soccer ball, which approximates the reality of the game. The Hoff circuit seems attractive for soccer players and has then been presented as a valid test for determining soccer players’ endurance performance (6). Indeed, the performance to dribbling the ball on the circuit as modified by VOLUME 29 | NUMBER 1 | JANUARY 2015 |
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Specific Aerobic Test in Soccer Players Chamari et al. (6) is correlated to the players’ maximal oxygen uptake. Recently, Zouhal et al. (26) have used the Hoff circuit with dribbling ball as a specific aerobic exercise; however, the exercise prescription on Hoff circuit is performed using heart rate (HR) (26) or with maximal effort (20). To our knowledge, no study has been carried out to evaluate whether it is possible to detect AT on the Hoff circuit with ball control/dribbling. In addition, the reliability and validity of AT determination on the Hoff circuit were not performed. If this is possible (i.e., reliability and valid), this would be a specific protocol for AT evaluation, training prescription, and determination of alterations soccer players’ physical fitness. Furthermore, because of the methodology limitation of MLSS assessment (i.e., high time required), the investigation of reproducibility and validity of the AT determined on the Hoff circuit through a unique incremental test would be very interesting for training practical purposes. In addition, between the AT methodologies, the speed corresponded to 3.5, 4.0 mmol$L21 and the intersection of 2 linear regressions (bisegmented method) have been used (9,12,18). These methods have already been validated to predict the MLSS during continuous running tests (9,12). Thus, the aim of this study was to test the reproducibility of these 3 methods of AT determination assessed on the Hoff circuit and to verify whether these AT methods can predict MLSS. We hypothesized that it is possible to determine the AT on the Hoff circuit using these 3 methods, and these methods are reliable and valid to predict MLSS of soccer players.
METHODS Experimental Approach to the Problem
To test the hypothesis that is possible to determine the AT on the Hoff circuit and that the AT is reliable and valid to
predict the MLSS, the present research was designed as an experimental cross-sectional study. This study was divided in 2 parts. In the first part of the study, our purpose was to determine the AT on the Hoff circuit and its reliability. In the second part of the study, we aimed to analyze the validity of AT for predicting MLSS intensity measured on the Hoff circuit. In the second part of the study 2, the MLSS was set as dependent variable, whereas AT on the Hoff circuit as independent variable. Primarily, the subjects were familiarized with the Hoff circuit. Then, they performed 5 progressive efforts on the Hoff circuit (6) to determine AT. The athletes completed 2 laps (580 m) at each speed, with an increment of 1 km$h21 per 2 laps. The AT on the Hoff circuit was determined through 3 different techniques (i.e., the speed corresponding to the 3.5 and 4.0 mmol$L21 and using the bisegmented method). The same protocol was repeated after 48 hours to verify its reproducibility. After these procedures, on separate days, the athletes performed random efforts of 100, 105, and 110% of ATHoff intensity for 30 minutes to detect the MLSS on the Hoff circuit (MLSSHoff ). Subjects
The sample size was calculated based on the assumption that AT is reliable and presents strong correlations with MLSS (r . 0.90). We used G*Power 3.1 software (Du¨sseldorf, Germany) to determine that a sample size of 10 subjects was the minimum needed to provide a statistical power of 90% with an alpha of 0.05 for the analysis. Therefore, a group of 16 soccer players (age = 16.0 6 1.0 years; body mass = 63.7 6 9.0 kg; lean mass = 52.4 6 6.1 kg; height = 169.4 6 5.3 cm; and fat percentage = 13.4 6 4.6%) took part in study 1 and a subgroup of 11 soccer players in study 2 (age = 15.8 6 0.6 years; body mass = 63.1 6 9.9 kg; lean mass = 52.0 6 7.0 kg; height = 169.0 6 6.3 cm;
TABLE 1. Comparison, coefficient of variation, effect size, and typical error in the values of anaerobic threshold determined by a fixed concentration of 3.5 mmol$L21 (ATHoff) and 4.0 mmol$L21 (ATHoff4,0), and through the bisegmented method (ATHoffBI).*† CV (%)
Test 10.0 6 0.8 (9.6–10.4) ATHoff (km$h21) HRAT-Hoff (b$min21) 195.2 6 19.0 (182.0–201.1) 10.7 6 0.7 (10.0–10.7) ATHoff4.0 (km$h21) HRAT-Hoff4.0 191.6 6 18.2 (185.1–205.3) (b$min21) 9.2 6 0.6 (8.5–10.0) ATHoffBI (km$h21) HRAT-HoffBI 181.0 6 13.4 (173.9–188.2) (b$min21)
Retest
7.94 10.2 6 1.1 9.35 192.5 6 18.7 7.14 10.7 6 1.2 9.73 188.0 6 17.9
(9.6–10.7) (178.1–198.5) (9.9–11.0) (182.1–203.1)
Effect size
CV (%)
0.218 10.80 0.225 9.58 0.2938 11.68 0.155 9.75
6.67 9.4 6 0.4 (9.1–9.6) 0.034 7.47 175.3 6 15.4 (167.9–185.2) 0.391
4.60 8.81
Typical error 0.44 11.93 0.57 13.33 0.47 8.01
*The values of HR of each intensity are reported (n = 16). The values are given as mean 6 SD (95% confidence interval). †ATHoff = anaerobic threshold determined by a fixed concentration of 3.5 mmol$L21; HRAT-Hoff = heart rate corresponding to ATHoff;
ATHoff4.0 = anaerobic threshold determined by a fixed concentration of 4.0 mmol$L21; HRAT-Hoff4.0 = heart rate corresponding to ATHoff4.0; ATHoffBI = anaerobic threshold determined by a bisegmented method; HRAT-HoffBI = heart rate corresponding to ATHoffBI.
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Figure 1. Mean 6 SD values and comparisons between MLSSHoff and ATHoff (A), MLSSHoff and ATHoff4.0 (B), and MLSSHoff and ATHoffBI (C). *p , 0.05 to MLSSHoff.
and fat percentage = 13.1 6 5.0%). They played in amateur competitions (competition experience at least 3 years, 3–4 training per week, 1.5–2 hours per training session) and voluntarily participated in this study. Body composition data were estimated using the DEXA scan (GE Lunar–DPX-NT; General Electric, Fairfield, CT, USA) (10,11). The informed consent was obtained from a legal representative for each of the subjects signed before their participation in the study. The experimental protocol was approved by the Research Ethics Committee of the Sao Paulo State University (Protocol No. 54/2010, Sao Paulo State University, Faculty of Sciences and Technology of Presidente Prudente) and was designed in accordance with the ethical standards of the Helsinki declaration. Determination of Anaerobic Threshold on the Hoff Circuit (ATHoff)
Before the experimental procedures, the subjects were instructed to maintain the habitual food intake and sleep behavior. In addition, during the tests, water was provided when requested. All tests procedures occurred in the afternoon, during training sessions, between July and September (competitive period). Before ATHoff determination, the subjects performed a familiarization trial on the Hoff circuit. Initially, without ball, the soccer players just ran at different speeds. Then, with the ball, the subjects dribbled through the circuit in different speeds controlled by sound stimulus. In a subsequent day, the players underwent 5 progressive efforts of 580 m (2 laps) on the Hoff circuit (6). The initial speed was
7.0 km$h21, and on each 2 successive laps, the speed was incremented to 1 km$h21 reaching 11 km$h21 for the last 2 laps. The speed was controlled by sonorous stimuli every 58 m. After each 2 laps at the same speed (i.e., 580 m), blood samples were collected (25 ml) from the earlobe to determine blood lactate concentration ([La2]). The HR was measured continuously using an HR monitor (Forerunner 410; Garmin, Olathe, KS, USA) and using a recording frequency of the data each 4 seconds. The [La2] was plotted vs. speed steps, and then were adjusted exponentially. The speed corresponding to the lactate concentration of 3.5 mmol$L21 was assumed as ATHoff, and the speed equivalent to 4.0 mmol$L21 was assumed as ATHoff4.0 (12). The AT was also determined using the bisegmented method as described by Matsumoto et al. (18). From these values, and the linear relation between speed and HR, the HR corresponding to the AT intensities was determined (HRAT-Hoff, HRAT-Hoff4.0, HRAT-HoffBI). The entire test was again performed after 48 hours to determine the reproducibility of these methods. Determination of the Maximal Lactate Steady-State Intensity on the Hoff Circuit
For MLSSHoff determination, the players were submitted to 3 random efforts of 30 minutes with speeds corresponding to 100, 105, and 110% of ATHoff. The choice of the 100% intensity of ATHoff instead of lower intensities was made because stabilization of blood lactate at 95% of ATHoff had been previously observed in a pilot study (M. Papoti, personal data). VOLUME 29 | NUMBER 1 | JANUARY 2015 |
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Specific Aerobic Test in Soccer Players These efforts were performed with the ball on the Hoff circuit (6) and were separated by a minimum of 24 hours and a maximum of 72 hours. Before the efforts and every 5 minutes subsequent to the efforts, a blood sample was collected as described above for [La2] determination. The MLSSHoff was assumed to be the intensity where [La2] presented a variation of no more than 1 mmol$L-1during the last 20 minutes of the effort (1). Blood Analysis
Twenty five microliters of blood was collected from the subjects’ earlobes and was deposited in 1.5-ml polyethylene tubes (Eppendorf, Sa˜o Paulo, SP, Brazil) containing 50 ml of 1% sodium fluoride. After this, 25 ml of the homogenized solution was added to an electrochemical lactate analyzer (1500 Sport model; Yellow Spring Instruments, Yellow Springs, OH, USA) (4).The electrochemical lactate analyzer was calibrated after every 5 blood samples analyzed using a 5.0 and 15 mmol$L21 lactate standard solution according to the manufacturer’s instruction. Blood lactate concentrations were expressed in millimoles per liter. Statistical Analyses
The data are expressed as mean 6 SD and 95% confidence interval (95% CI). The normality and homogeneity of the data were confirmed with the Shapiro-Wilk’s and Levene’s tests, respectively. To verify the reliability of the different methods of AT measures, the comparison between test
and retest values was analyzed using the paired Student’s t-test, intraclass correlation (ICC) test, typical error, and coefficient of variation (CV). To verify the differences and the agreement of the AT intensities to MLSSHoff and thereby to confirm the validity, we used the Bland and Altman analyses (3), Student’s t-test, and ICC test. The effect sizes (ESs) obtained in each statistical analysis were also presented and interpreted as proposed by Hopkins (www.sportsci.org/ resource/stats), with ES ,0.2 considered as trivial, small between 0.2 and 0.5, moderate between 0.6 and 1.1, large between 1.2 and 1.9, and very large .2.0. The significance level was fixed to be 5% (p # 0.05).
RESULTS The AT values determined through the 3 methods are described in Table 1. No significant difference (p . 0.05) was found between test and retest values of ATHoff, ATHoff4.0, and ATHoffBI, as well as between HR associated with the AT speed. In addition, the effect sizes for these comparisons were considered between trivial and small. Significant correlations were found between test and retest values for ATHoff (ICC = 0.79; p # 0.05) and ATHoff4.0 (ICC = 0.69; p # 0.05); however, ATHoffBI did not present a significant correlation. There was a significant intraclass correlation between test and retest for HRAT-HoffBI (ICC = 0.70; p # 0.05) and HRAT-Hoff (ICC = 0.56; p # 0.05). The typical error for AT determined through the 3 methods
Figure 2. Average of systematic error, upper and lower limits of the agreements obtained by Bland and Altman (3) and between MLSSHoff and ATHoff (A), MLSSHoff and ATHoff4.0 (B), and MLSSHoff and ATHoffBI (C).
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Journal of Strength and Conditioning Research varied between 0.44 and 0.57 km$h21, and the HR relative to the AT presented a typical error between 8.01 and 13.33 b$min21. The MLSSHoff corresponded to 10.6 6 1.3 km$h21 (95% CI = 9.5–11.3 km$h21) and was not statistically different from ATHoff4.0 (95% CI = 9.6–11.1.3 km$h21; ES = 0.067, trivial); however, it was higher than ATHoffBI (95% CI = 9.2– 9.7 km$h21; ES = 1.027, moderate) and ATHoff (95% CI = 9.2–10.8 km$h21; ES = 0.298, moderate), the latter of which underestimated MLSSHoff by only 3.4%. These values are shown in Figure 1. Besides this, MLSSHoff showed a high ICC with both ATHoff (ICC = 0.94; p # 0.05) and ATHoff4.0 (ICC = 0.80; p # 0.05), whereas ATHoffBI did not present any significant correlation with MLSSHoff. The Bland and Altman analysis revealed good agreement between MLSSHoff, ATHoff, and ATHoff4.0 (Figures 2A, B, respectively), as the bias was close to zero, and the agreement limits demonstrated that the difference between the 2 measurements was of only 1.33 km$h21.
DISCUSSION The aims of this study were to determine the reproducibility of the AT determined on the soccer-specific Hoff circuit (6) using 3 different methods and to verify whether this AT could predict the MLSS. The main findings were (a) the AT determined on the Hoff circuit was reproducible because no difference was found between test and retest for any method of AT determination, a trivial to small effect size on differences and the typical error of the 3 methods of determination were very small; (b) the ATHoff4.0 did not present difference and was strongly correlated with MLSSHoff, and ATHoff underestimated the MLSSHoff speed by only 3.4% and was significantly correlated with it. These results confirm partially our initial hypotheses because only the ATHoff4.0 was considered valid to predict MLSS. The AT determined through the 3 methods on the Hoff circuit were reliable. Only ATHoffBI did not present correlation between test and retest; however, the within-subject variation of the AT was within 0.57 km$h21, which suggests that, independent of the method of determination, the speed is very reproducible and could be used for the assessment. Williams et al. (25) also studied the reliability of a field test to evaluate the aerobic fitness of university soccer players. However, the only analyzed variable was the time to perform 4 laps on the field circuit. On the robust study of Krustrup et al. (17), they verified that the Yo-Yo intermittent recovery test (level 1) is reliable and can be used as a precise measure of physiological performance in soccer players. Williams et al. (25) observed a higher ICC than this study (r = 0.98 vs. r = 0.79, respectively), whereas the correlation coefficient of Krustrup et al. (17) was 0.98. However, these studies did not report the typical error and, as proposed by Hopkins (15), the typical error is the best way to analyze within-subjects’ variation. This study verified a variation between 0.44 and 0.57 km$h21, and this would be of poten-
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tial value for training prescription and/or detecting training effects because a variation of above 0.57 and below 0.44 km$h21 might indicate an improvement or decrease in physical fitness, respectively (22). In the context of aerobic fitness in soccer players, the determination of AT is essential. Helgerud et al. (13) showed that if the AT increases, then the ball involvement and number of sprints also improve. As observed on the AT, the HR corresponding to the AT of the 3 methods of determination did not present any statistical difference. The HRAT-HoffBI and HRAT-Hoff presented moderate and low significant ICC values, respectively, whereas the HRAT-Hoff4.0 did not present correlation. However, together with the relatively small typical error shown in the study, the small CV indicates that the AT HR is reliable. Thus, the HR corresponding to the AT can be used as a reliable tool for controlling and prescription of training, especially it usually does not change during a season, even with an increase in aerobic fitness (5,19). This study did not display differences between ATHoff4.0 and MLSSHoff. ATHoff and ATHoff4.0 had significant correlation with MLSSHoff (ICC = 0.94 and 0.89; p # 0.05, respectively). To our knowledge, this is the first study to validate the AT evaluation on the Hoff circuit. Besides the absence of differences and the high ICC values, only ATHoff4.0 presented a relatively good agreement limit and small bias (20.37) with MLSSHoff. These findings indicate that ATHoff4.0 is an interesting and simple method for estimating MLSSHoff. It is worth noting that ATHoff underestimated MLSSHoff by only 3.4% and presented very high ICCs of 0.94 (p # 0.05). To our knowledge, this is the first study to validate a specific soccer AT test to predict MLSS. This result can increase the use of this specific test to evaluate soccer players’ aerobic capacity and the use of this intensity for training prescription. However, the sensibility of these methods for AT evaluation still needs to be investigated in future studies. The ATHoff underestimates the MLSS by only 3.4%, whereas the ATHoff4.0 was not different from the MLSS. Usually, the AT corresponded to the fixed [La2] of 4.0 mmol$L21 is attained on incremental tests with stages during around 5 minutes (12). Jones and Doust (16) did not find any difference between MLSS and AT in runners using a fixed [La2] of 3.5 mmol$L21 and stages during 3 minutes. Contrary, this study used a stage length of z5 minutes, and the AT with a fixed [La2] of 4.0 mmol$L21 was not different from the MLSS. The hypothesis for this result is that Sassi et al. (21) verified that the energetic cost increases when the subjects are evaluated on an absorptive surface (grass). Because the cost is higher, the [La2] for the same intensity would be higher (7). Thus, when evaluating AT specifically, independent of the effort stage length (12), the fixed concentration of 4.0 mmol$L21 should be used. To conclude, the AT determined on the Hoff circuit through 3 different methods is highly reproducible, as well as the HR relative to AT. Considering the good agreement between ATHoff and ATHoff4.0 and MLSSHoff, this test can be VOLUME 29 | NUMBER 1 | JANUARY 2015 |
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Specific Aerobic Test in Soccer Players used to predict MLSS in young soccer players, with the latter showing the best accuracy.
PRACTICAL APPLICATIONS This study provided a new method to determine the AT of soccer players, which is useful because it considers the common direction changes performed by soccer players during a match and the technical demands of the game. In addition, this method is more attractive for athletes because of the involvement with the soccer ball. In summary, the use of this aerobic capacity determination method may increase the adherence of the soccer players and be closer to the game reality, providing a more reliable index for training prescription. Anaerobic threshold determination on the Hoff circuit has wide applications for coaches and fitness coaches and could be used for the following: Training prescription: The ATHoff or ATHoff4.0 could be used to prescribe continuous endurance training or interval training with higher. The HR relative to the AT could be used to control training on the Hoff circuit or possibly in small-sided games because both are performed on grass and need ball control. Monitoring the effects of training: Due to the small typical error (z0.44 km$h21; Table 1), any increase in AT wide above or under this value should be accepted as a significant alteration of endurance fitness.
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