RATING OF MUSCULAR AND RESPIRATORY PERCEIVED EXERTION IN PROFESSIONAL SOCCER PLAYERS ASIER LOS ARCOS,1 JAVIER YANCI,1 JURDAN MENDIGUCHIA,2
AND
ESTEBAN M. GOROSTIAGA3
1
Department of Physical Education and Sport, Faculty of Physical Activity and Sport Science, University of the Basque Country, UPV/EHU, Vitoria-Gasteiz, Spain; 2Department of Physical Therapy, Zentrum Rehabilitation and Performance Center, Pamplona, Spain; and 3Studies, Research and Sport Medicine Center, Government of Navarre, Pamplona, Spain ABSTRACT
Los Arcos, A, Yanci, J, Mendiguchia, J, and Gorostiaga, EM. Rating of muscular and respiratory perceived exertion in professional soccer players. J Strength Cond Res 28(11): 3280–3288, 2014—This study investigated, in male professional players: (a) fluctuations in rating of local-muscular (sRPEmus) and central-respiratory (sRPEres) perceived exertion measured after the completion of each training and competitive session, over a 9-week competitive period and (b) the influence of quantitative assessment of different training and competition modes on changes in physical performance. sRPEres, sRPEmus, and heart rate were measured in 21 players in 847 individual training and competitive sessions. Training load was calculated by multiplying sRPEmus or sRPEres by the duration of the training or competition sessions. A test battery (vertical jump, sprint, and endurance running) was performed before and after the studied period. At the end of official matches, average sRPEmus was higher (7.4 6 0.6; p # 0.05) than sRPEres (6.4 6 1.3). Significant negative correlations were observed between the values of total training and competition time (r = 20.62; p , 0.01) or total added sRPEmus (r = 20.59; p # 0.05), and vertical jump or sprint running velocity changes, respectively. This suggests that sRPEmus should be considered the main fatigue rating during a soccer match. Training and competition volume may have negative effects on the muscle power performance gains of the legs.
KEY WORDS soccer, training, match, training load, physical performance
INTRODUCTION
A
ccurate assessment of the physiological stress imposed on the athletes, called physiological training load (TL) (17), is a key factor used to monitor and control the training and competition
Address correspondence to Javier Yanci, [email protected]. 28(11)/3280–3288 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
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process, to prevent under and over training, and to ensure that each athlete is in optimal condition for competition (25). This is particularly important in team sports, where individual differences in physiological responses to the imposed training and competition load occur (23,34). One of the most objective methods for quantifying TL in long duration effort is heart rate (HR) monitoring during training sessions (1,26). However, the routine recording of HR monitoring is only limited to scientific research and a few top professional teams (25), due to problems such as technical expertise, the time-consuming process of collecting HR data from all team players in every training session, the uncomfortable feeling of wearing the device during soccer practice, and the cost of several HR telemetric systems (25). Foster et al. (14–17) were the first to propose a subjective alternative method for evaluating TL in endurance and team sport athletes. This simple, valid, cheap, and reliable method, called “overall session rating of perceived exertion (sRPE),” represents the athlete’s own perception of training stress and gives a more holistic indication of the global physiological load because it is indicative of both physiological and psychological parameters (37). It is also intended to encourage players to view the training session as a whole (17). It calculates physiological TL by multiplying the individual overall sRPE, using a 0–10 scale as a measure of exercise intensity of the whole training session (16), by the duration of the session (in minutes). This product, named session rating of perceived exertion training load (sRPE-TL), represents the magnitude of physiological TL in arbitrary units (AUs), in a single number, and it seems to provide a valid and reliable measure of the physiological TL when both anaerobic and aerobic systems are appreciably activated, as is the case during soccer training and match play (2,25,44). Several descriptive studies performed over a few weeks with speed skaters (14), male basketball players (16,34), and young (1,25) professional soccer players (26,28) have described the mean most common weekly physiological TL using sRPE-TL. These descriptive studies have never provided evidence, however, of the utility of TL assessed by sRPE-TL over several weeks of training to predict or represent changes in the main physical performance characteristics of adult professional soccer players (1,8). This
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Journal of Strength and Conditioning Research assessment is of interest because a controlled research design to determine the best manipulation of TL to improve soccerspecific physical performance is lacking and could be useful to guide the training process (34). The above-mentioned studies measured an “overall” perceived exertion rating, which probably integrates a variety of information, including the many signals elicited from the peripheral working muscles and joints, the central cardiovascular and respiratory functions, and the central nervous system. Some authors (13,38) proposed differentiated ratings of perceived exertion in comparison with the overall measure, to provide a better explanation of the mechanisms by which the subjective perception of exertion is determined during physical work. They distinguished 3 ratings of perceived exertion (RPE), devoted to: (a) “local” or “muscular” (RPEmus, i.e., the feeling of strain in the working muscles), (b) “central” or “respiratory” (RPEres, i.e., perceived tachycardia, tachypnea, and even dyspnea), and (c) “overall” (RPE overall). To the best of our knowledge, there are no published studies that have dealt with local-muscular and central-respiratory perceptions during soccer training and competition sessions, nor published studies quantifying physiological TL that differentiate sRPEmus and sRPEres during whole training and competition sessions over several weeks in this population. The distinction between sRPEmus and sRPEres can be considerable in soccer because toward the end of a match, a muscle fatigue scenario (5,35,36,41) seems to coexist with only a submaximal involvement of the cardiovascular and respiratory system (75% of maximal oxygen uptake, 80–90% of maximal HR) (5,36,46). In this regard, the assessment of the physiological sRPEmus and sRPEres-TL, called sRPEmus-TL and sRPEres-TL, respectively, could result in a better understanding of the required TL needed to optimize the training process in team sports. The purposes of the study were therefore: (a) to investigate the training and competition fluctuations in sRPEmus, sRPEres, and TL monitored over a 9-week in-season competitive period in professional players and (b) to determine the influence of the quantitative assessment of different training and competition modes on changes in physical performance over the course of that competition period. One hypothesis was that sRPEmus and sRPEres would differentiate RPE during training and matches. It was also hypothesized that the quantitative assessment of different training variables could be related to changes in physical performance.
METHODS Experimental Approach to the Problem
The study was performed during the in-season competitive period (from September to May) in a 9-week period from October to December, and it began 9 weeks after the end of a 5-week preseason period. A global feeling of strain in the working muscle and the other central (respiratory), on global perceived tachycardia, tachypnea, and even dyspnea of the
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whole training session or match was solicited from each participant 10 minutes after completion of each training and competition session. Also, HR was recorded during training sessions. The participants were tested for anthropometrical variables and vertical jumping capacity, maximal sprint, and running endurance before and after the 9-week period using identical protocols, to determine the changes in physical performance over the course of that competitive period. Subjects
Twenty one Spanish male professional soccer players (age = 21.0 6 1.7 years; body height = 181.0 6 6.3 cm; body mass = 76.1 6 7.7 kg) in a third division team, made up of players belonging to the youth team of a professional elite first division team, participated in this study. Players usually performed 4–6 training sessions per week, plus 1 official match. Before the beginning of the study, written informed consent was obtained from all players. The participants and coach were informed about the experimental procedures and the possible risks and benefits of the project, which was approved before the start of the study by the local institutional review board for use by human participants, according to the Declaration of Helsinki. Procedures
Tests were performed after 1 day of minimal physical activity, on 1 day, in a fixed order and in the same facilities. Before the physical tests, each participant was subjected to anthropometrical measurements. After, vertical jump and sprint and endurance running tests were performed. The goalkeepers (n = 2) did not perform the endurance running test. Testing was integrated into weekly training schedules. The participants were familiarized with the testing protocol because they had been tested on several occasions in previous seasons for training prescription purposes with the same procedures. In a pilot study, the intertest reliability for measuring anthropometrical variables, together with several endurance indices, had been assessed on 2 trials, separated by 7 days, in a group of team sport players. The testretest intraclass correlations coefficients (ICCs) of the anthropometric and vertical jumping variables used in this study were .0.91 and the coefficients of variation (CV) ranged from 0.9 to 7.3%. Similarly, the ICC and CV for the velocity associated with a fixed submaximal blood lactate concentration were 0.94 and 2.2%, respectively. Jumping Test. On an indoor court, the participants did the jumping test after a standardized 15 minutes warm-up period. The participants were asked to perform a maximal countermovement vertical jump, on a jumping mat (Newtest OY, Oulu, Finland), with the hands fixed on the hips. The participants performed the jump from an extended leg position, down to 908 knee flexion, immediately followed by a subsequent concentric action for maximal height where the participants were instructed to land on the contact platform in a position similar to that of the take-off. The jumping VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Perceived Exertion in Soccer
TABLE 1. Anthropometric and physical characteristics values at the beginning (pretest) and at the end (posttest) of the 9-week competitive period.* Variables Body mass (kg) CMJ (cm) SPR5 (s) SPR15 (s) Lac10 min (mmol$L21) Lac25 min (mmol$L21)
n
Pretest
21 18 16 16 16 16
76.1 43.3 0.96 2.28 2.89 3.16
6 6 6 6 6 6
7.7 5.0 0.03 0.07 0.72 0.73
Postest
Change (%)
6 6 6 6 6 6
0.52 1.61 0.00 0.00 1.38 0.94
76.5 42.6 0.96 2.28 2.85 3.13
7.4 4.5 0.04 0.07 0.49 0.71
*CMJ = countermovement jump; SPR5 = 5-m sprint time; SPR15 = 15-m sprint time; Lac10 min = blood lactate concentration value at 10 minutes during the endurance running test; Lac25 min = blood lactate concentration value at 25 minutes during the endurance running test.
height was calculated from the flight time. Two sets of 3 maximal jumps were recorded, interspersed with approximately 10 seconds rest between jumps and 90 seconds rest between sets. The best reading was used for further analysis. Maximal Sprint and Endurance Running Test. Ten minutes after completion of the jumping test and after a standardized warm-up period for sprint running, participants undertook a sprint running test consisting of 3 maximal sprints of 15 m on an indoor court, with 90 seconds rest between each sprint. Fifteen meter was chosen because is the average sprint length observed during official matches in elite soccer players (7). During the 90-second recovery period, the participants walked back to the starting line. The recording of running time was done using photocell gates (Newtest OY, Oulu, Finland) placed 0.4 m above the ground with an accuracy of 0.001 seconds. The participants commenced the sprint when ready from a standing start, 0.5 m behind the start and the sprint start was self-initiated. Stance for the start was consistent for each participant. The time was automatically activated as the participant passed the first gate at the 0-m mark, and split times were recorded at 5 and 15 m. The lowest time was selected for further analysis. The endurance running test was performed 10 minutes after the end of the sprint running test on an artificial outdoor grass soccer court (1003 50 m). Each participant performed a 2-stage constant submaximal velocity running test with a 2-minute rest between each run. Time for the first stage was 10 minutes, and for the second stage, 15 minutes. For each participant, the running velocity corresponded to the individual value of the velocity associated with a blood lactate concentration of 3 mmol·L21, obtained by extrapolation during a previous preliminary 4-stage submaximal discontinuous progressive running test, explained in detail elsewhere (20). To assure a constant velocity, participants were instructed to run at an even pace through an audio signal connected to a preprogrammed computer. Immediately after each exercise stage, and after cleaning and puncturing,
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a 5-ml sample of whole blood was automatically aspirated from a hyperemized earlobe into a single-use enzyme-coated electrode test strip. Lactate concentration was determined through amperometric measurement, and the result displayed in 60 seconds (Lactate Pro LT-1710; Arkray KDK Corporation, Shiga, Japan). In terms of reliability, the manufacturers report a CV of 3.2 and 2.6% with lactate standards of 2 and 11 mmol$L21 respectively. Although the velocities of this endurance constant velocity running test differed between participants, they were the same in each participant before and after the 9-week period (11.9 6 0.4 km·h21). Our criterion of endurance capacity was the blood lactate concentration elicited during submaximal exercise at a given velocity _ O2max because it has been shown to be more sensitive than V in the physiological outcome in soccer (26). Training and Competition Data Analysis. Training session duration ranged from 60 to 85 minutes. The heaviest aerobic training exercise was usually completed 4 days before the match day (M-4) and consisted of continuous running or interval training. Three days before the match (M-3), 20 minutes were generally dedicated to speed development or to heavy resistance training consisting mainly of sprint, plyometric, half-squat, and jumping exercises. The rest of the training usually consisted of various skill activities at different intensities, small-sided games with individual technical and tactical objectives, offensive and defensive strategy, and 3 3 7 minutes of continuous play. Each participant was monitored in every training and competition session by one of the researchers, who was the physical conditioning coach of the team. Diet or lifestyles were not controlled during the course of the study, although some of the players were encouraged to maintain body weight. Determination of Physiological Training Load. Approximately 10 minutes after the completion of each training session or match, a rating of the difficulty of the whole training session or match was solicited from each participant, except the
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of getting an uncomplicated response that reflects the athlete’s global impression of the workout (15). We delayed securing the session sRPE rating for 10 minutes so that particularly difficult or particularly easy segments toward the end of the exercise bout would not influence the participant’s rating (14) too much. The participants had to differentiate between 2 types of RPE: 1 local (leg, muscular), regarding the global feeling of strain in the working muscle, named sRPEmus, and the other cenFigure 1. Average time corresponding to 3 HR zones (,70, 70–90, and .90% of HRmax), during the 4 training days preceding the competition day (match, M) at the most typical weekly microcycles (match on Sundays and the tral (chest, respiratory), on following Saturdays). HR was collected for 167 individual training sessions in 19 players. The number of HR global perceived tachycardia, recordings per player ranged from 36 to 49. M-4: n = 16, 43 occasions; M-3: n = 16, 38 occasions; M-2: n = 16, tachypnea, and even dyspnea, 47 occasions; M-1: n = 16, 33 occasions. HR = heart rate; HRmax = maximum heart rate. named sRPEres (13,38). Each player completed the RPE scale without the presence of goalkeepers, using the 0–10 point Borg’s category RPE scale other players, and they could not see the values of other (9), modified by Foster et al. (14,17). A Spanish translation of participants. Players were allowed to mark a plus sign (interpreted as 0.5 point) alongside the integer value if they this scale was used. We explained to the participant that we wished (16). Participants were familiarized with the use of wanted a global rating of the entire training or competition the 10-point scale before the data collection for this study bouts, using whatever cues they felt to be appropriate. The athlete responded to 2 simple questions, always asked in this over a month. The duration of a training or match session order—How intense was your session on your chest? and was recorded for each player from the start to the end of the How intense was your session on your legs?—With the aim session, including recovery periods but excluding time devoted to stretching exercises during training sessions and time spent on warm-up and half-time during match sessions. An exercise score, which has been called the session training or competition “load,” was computed by multiplying the duration of the training or competition session by the sRPEres or sRPEmus, as described by Foster et al. (16,17). The session training or competition loads were named sRPEres-TL or sRPEmus-TL, and measured in AU. Daily and weekly sRPEmus-TL and sRPEres-TL were calculated from the sum of all training and competition sessions performed in a day and week, respectively Figure 2. Average (6SD) sRPEres and sRPEmus values after the match depending on the minutes played per match. *p # 0.05: significant differences between sRPEres and sRPEmus. #p , 0.01: significant differences (14,25). Total weekly sRPEmusbetween ,20 or 20–45 and .70 in sRPEres. ^p , 0.01: significant differences between ,20 or 20–45 and TL and sRPEres-TL were taken .70 in sRPEmus; ,20 (n = 9 players; 18 occasions), 20–45 (n = 11 players; 17 occasions), and .70 (n = 15 as an average of the 9 weekly players; 78 occasions). sRPE = session rating of perceived exertion. training cycles. VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Perceived Exertion in Soccer analyzed. The physiological intensity of all training sessions were indicated by both mean absolute (beats per minute) and relative values (i.e., the corresponding percentage of maximum heart rate; % HRmax) of HR. The time spent within specific HR zones (.90, 70–90, and ,70% HRmax) was also measured. Maximum heart rate was estimated to be 10% higher than the average HR recorded during the last 10 minutes of the endurance running test (29,45). To validate the sRPEres and sRPEmus to monitor training Figure 3. Representation of the daily training and competition load determined using mean sRPEres-TL and and competition loads in team sRPEmus-TL during the more representative competitive week (n = 12). *p , 0.01 significant differences between sports, we examined the inditraining days in sRPEres-TL or sRPEmus-TL. #p , 0.01 significant differences between trainings and match in sRPEres-TL or sRPEmus-TL. M-4: n = 19, 77 occasions; M-3: n = 19, 78 occasions; M-2: n = 19, 76 occasions; vidual relationships between M-1: n = 19, 72 occasions; match: n = 12 players, 26 occasions. AU = arbitrary unit; sRPE = session rating of sRPE and an objective measure perceived exertion; TL = training load. of internal load (HR). To do this, the RPE TLs for each training session or match The players, except the goalkeepers, wore HR monitors (sRPEres-TL and sRPEmus-TL) were calculated as previously (Polar Team Sport System; Polar Electro Oy, Kempele, Finland) reported in this study. In addition, the individual product of the during all the training sessions as an objective reference method accumulated training duration in 5 HR zones by a coefficient for quantifying each training session. Heart rate was recorded at relative to each zone (from 50 to 60% of HRmax = 1 to 90– 5-second intervals. No HR was recorded during matches 100% of HRmax = 5) was computed and summated for each because of the prohibition of wearing HR monitors and belts training session, as proposed by Edwards (12). The HR-based during official competitive matches. All players were regularly TL scores (HR-TL) and the sRPEres and sRPEmus-TL scores asked to check their HR monitors during each training session. (sRPEres-TL and sRPEmus-TL, respectively) were calculated After each training session, HR data were downloaded to from an average of 27 6 4.5 training sessions per player. a portable PC using the specific software and exported and Regression analysis showed that the individual correlations
Figure 4. A) Relationship between the values of total accumulated time devoted to (training + match), and the individual relative changes of vertical jumping performance (in percentage of the initial values), during the 9-week experimental period. B) Relationship between the individual values of total added (training + match) sRPEmus and the relative changes in 15-m sprint running velocity (in percentage of the initial values), during the 9-week experimental period. CMJ = countermovement jump.
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between sRPEres-TL and HR-TL were all significant (p , 0.01), from r = 0.67 to r = 0.91 (average: 0.87 6 0.06). Similarly, individual correlations between sRPEmus-TL and HR-L were all significant (p , 0.01) from r = 0.67 to r = 0.91 (average, 0.84 6 0.07). The magnitude of the individual correlations is in agreement with that reported by previous investigators measuring overall sRPE-TL and HR-TL values in team sports players (16,25,44) during practice sessions. This suggests that the sRPEres-L and the sRPEmus-TL methods provide approximately the same information as the HR-based method, and they could be considered a good tool to monitor internal TL in team sports such as soccer (14,25).
following Saturday, and this was considered the most typical weekly microcycle. At this typical microcycle, the mean total time spent by 16 players in 3 HR zones (,70, 70–90, and .90% of HRmax) during the 4 training days preceding a match day is shown in Figure 1. On these training days, the global relative contributions of each HR zones were 50.2 6 19.9% (,70% HRmax), 40.5 6 16.0% (70–90% HRmax), and 9.3 6 10.0% (.90% HRmax). Three players were not included in the HR analysis because their recorded session number was low (,4) due to HR recording problems or low attendance at the training sessions in these typical weekly microcycles.
Statistical Analyses
Session Rating of Perceived Exertion Scores After Matches
Standard statistical methods were used for the calculation of the mean values and SDs. Data were screened for normality of distribution and homogeneity of variances using a Shapiro-Wilk normality test. The changes in physical performance over the course of the 9-week experimental period were compared using Student’s paired t test. A 2 3 3 (playing match time) analysis of variance condition (condition 3 time) with repeated measures was used to determine mean differences. Significant differences between mean values were identified using a Bonferroni’s post hoc test. Pearson’s product-moment correlations coefficients (r) were used to determine the relationships between changes in fitness parameters and physiological load values. The following scale of magnitudes proposed by Hopkins (24) was used to interpret the correlation coefficients: ,0.1 = trivial; 0.10–0.29 = small; 0.30–0.49 = moderate; 0.50–0.69 = large; 0.70–0.90 = very large; and .0.90 = nearly perfect. Statistical significance was set at p # 0.05. Data analysis was performed using the Statistical Package for Social Sciences (version 18.0 for Windows; SPSS Inc., Chicago, IL, USA).
Since 3 substitutions are allowed in a soccer match, the number of minutes played at each match varied widely within and between subjects. Thus, there were 9 subjects who played less than 20 minutes per match on 18 occasions, 11 who played between 20 and 45 minutes per match on 17 times, and 15 who played more than 70 minutes on 78 occasions. A repeated-measures analysis of variance indicated that the pattern of sRPEres and sRPEmus response differed (p , 0.01) as the match progresses (Figure 2). Thus, when players played less than 20 minutes per match, average sRPEmus (;3.3) was lower (p , 0.01) than average sRPEres (;4.4), whereas when they played between 20 and 45 minutes per match, average sRPEmus and sRPEres were similar (;4.3–4.7). However, when the players played more than 70 minutes per match, average sRPEmus at the end of the game was very high (;7.4) and significantly higher (p # 0.05) than sRPEres (;6.4).
RESULTS Anthropometric Characteristics and Changes in Physical Performance
The data on anthropometric characteristics and physical performance values at the beginning and at the end of the studied period are presented in Table 1. No changes occurred in body mass, vertical jumping performance, and sprint running time during this period. Before the experimental period, average blood lactate concentration remained stable (;3 mmol$L21) between 10 and 25 minutes at the constant velocity endurance running test performed. No changes in mean blood lactate concentration were observed at this same absolute running velocity during the experimental period. Times Spent at Training and in Heart Rate Zones
During the experimental period, each player performed an average of 40 training sessions (4.8 training sessions per week), for a total average duration of 2,848 minutes. The team played 9 matches during the experimental most frequent match sequence (4 weeks) from Sunday to the
Session Rating of Perceived Exertion Training Load Scores at Training and Competition
sRPEres and sRPEmus were collected for 847 individual training sessions and for 120 individual matches. Figure 3 shows the pattern of the average sRPEres-TL and sRPEmus-TL profiles during the more typical weekly microcycle that comprised 1 match on day “M-6” and the following match on day “M” (from Sunday to Saturday). For descriptive purposes, all data were used for the training sessions but only data of players playing more than 70 minutes (n = 12) were used for the match score. A significant main effect over time was observed (p , 0.01). We did not observe a main effect for condition (sRPEres-TL vs. sRPEmus-TL) or a condition 3 time interaction (p . 0.05). Mean comparisons for training days were all significantly different (p , 0.01). The highest TL scores were observed at (M-3), and the lowest values were observed at (M-1), whereas at M-4 and M-2, the score values were between those observed in M-3 and M-1. The highest scores of the week were observed on the match day in the players playing .70 minutes per game, and they were approximately 100% greater than those observed during the hardest training day. No differences were observed in a day between sRPEres-TL and sRPEmus-TL scores. Total (training + match) average VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Perceived Exertion in Soccer weekly sRPEres-TL and sRPEmus-TL were 1515 6 134 and 1576 6 147 AU, respectively. Relationships Between Quantitative Assessment of Training and Competition and Physical Characteristic Changes
Large significant inverse linear correlations were observed during the study between the accumulated values of total added (training + match) times and relative changes in vertical jump performance (r = 20.62; p , 0.01; n = 18) (Figure 4A). Similarly, large significant inverse correlations were observed between the total added (training + match) sRPEmus values and the individual relative changes in 15-m sprint running velocity (r = 20.59; p # 0.05; n = 15) (Figure 4B).
DISCUSSION One of the main findings of this study was that players playing more than 70 minutes per match had a very high average sRPEmus at the end of the game (;7.4), significantly higher than sRPEres (;6.4). Higher sRPEmus than sRPEres values at the end of exhausting exercise is in agreement with exhausting cycling studies performed in healthy moderately trained young (18) and middle-aged (10) men. This suggests that at the end of a soccer match, professional players have a higher subjective perception of strain from their peripheral working muscles and joints than from their central cardiovascular and respiratory functions. From the existing data, it cannot be determined whether sRPEmus is linked directly with muscular fatigue or it can also be attributed, at least in part, to additional inputs from other peripheral organs and from the central nervous system. Nevertheless, the very high feeling of strain in the working muscles toward the end of a professional soccer match may be related to some physiological changes occurring inside the muscle. Several studies on amateur and professional (5,32,42) soccer players have found abrupt alterations in muscle cells at the end of official or unofficial matches, such as a reduction of muscle glycogen stores (5,42), with nearly half of the muscle fibers being completely or almost empty of glycogen (31,32), a very high rate of lactate production and muscle acidosis during periods of high intensity in a match (5,31,32), deterioration of muscle sarcoplasmic reticulum function (33), accumulation of potassium in the muscle interstitium (6), low or depleted muscle creatine phosphate concentrations in individual muscle fibers (31), and reduced muscle ATP stores in individual fibers (5,32). Furthermore, increases in the expression of reliable markers for muscle cell, muscle cell disruption, or oxidative damage occur at the end of soccer matches and are reflected by elevated levels of blood ammonia/ammonium (NH3) (5,32), uric acid (4,5), malondialdehyde (4), protein carbonyls (27), myoglobin (4,33), lactate dehydrogenase (27), and creatine kinase (4,27,40). Bangsbo (5) has suggested that these muscular and blood changes may show a fatigue scenario in which the recruitment of the fast-twitch muscle fibers to generate force decreases during a match because they become progressively fatigued. Assuming that muscle
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force, velocity, and power production are indicators of local muscle status (43), this muscle fatigue scenario is corroborated by a significant decline in the amount of high-intensity running (35), sprinting ability (4,27,32,41) and the forcegenerating capacity of knee extensor (4,27), and flexor (4) muscles observed toward the end of a match in top youth (41), amateur (4,32), and professional soccer players (27). The observation that the substitutes who came on in the second half perform more high-intensity running and more sprinting than players playing the entire game (35) supports the notion that the lower match intensity and physical performance during the last phase of a match is caused by match-induced fatigue. This provides support to the suggestion that leg fatigue is most dominant factor toward the end of a match for players who play more than 70 minutes (39). Although sRPEmus in the players playing more than 70 minutes per match was strong and higher than sRPEres, the pattern of sRPEres and sRPEmus response differed as the match progresses. Hence, when players played less than 20 minutes, average sRPEmus was “moderate” (;3.3) and lower than average sRPEres (;4.4), whereas when they played between 20 and 45 minutes, average sRPEmus and sRPEres were similar (;4.3–4.7), between “somewhat strong” and “strong.” This indicates that sRPEres increases less abruptly than sRPEmus as the match progresses. It has been assumed that oxygen uptake and HR are closely related to central factors (cardiac and pulmonary output) (43), and sRPEres is a good correlate for central cardiovascular and respiratory strain perception (11). The lower increase in sRPEres observed along the game could be related to the fact that relative work intensity (a central cardiorespiratory index) is only submaximal, around 70–75% V_ O2max or between 80 and 90% of HRmax (46) during the first half, and even declines slightly during the second half of a soccer match (5,33,36,40). The magnitude of these central changes is much lower than the above-mentioned changes that occur within the muscle cells as the match progresses. It is suggested that in soccer matches longer than 70 minutes, sRPEmus is more sensitive than sRPEres in detecting fatigue. A clear training and match load profile was observed during the most representative week, which included 1 competitive official match. Training load built up to a midweek peak, and this was followed by subsequent sessions of less activity as a taper for the weekend match. This weekly profile is similar to that previously observed in professional basketball players and in young (25,47) and professional soccer players (5,26,28) playing once a week. The tapering strategy used during the 2 days preceding the match may be linked to the need to provide adequate time to recover before the next match, and it has been reported to be most effective in inducing positive effects on performance in endurance sports (34). The match sRPEres-TL and sRPEmus-TL values (;625–650 AU) of the players playing more than 70 minutes per match (Figure 2) is consistent with the overall sRPE-TL observed in young (25) and
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Journal of Strength and Conditioning Research professional (26) soccer players and mostly represents the main TL of the week. However, the total (training and match) accumulated weekly sRPEres-TL or sRPEmus-TL values in our study (;1.500–1550 AU) were 25–60% lower than the accumulated weekly overall sRPE-TL (;2.100– 3.900 AU) previously reported in young (1,25,47), and professional adult (3,26) soccer players in a typical in-season week with 1 match to play. Besides, in these 3 studies, there was at least 1 weekly training session in which the overall sRPE-TL was similar or higher in magnitude to the one observed during the match, whereas in our study, the highest training sRPEres-TL or sRPEmus-TL values were 50% lower than the corresponding match sRPE-TL values. It is difficult to compare the results of these studies because they can differ markedly in a number of factors, including times of measuring sRPE (10–30 minutes after the end of the session), type of sRPE recorded (overall or differentiated RPE), excluded activities during time recording (e.g., warm-up, stretching time, etc.) and influences of instruction, experimental design, rating behavior, cultural differences, and context effects (11). The main explanation for the observed differences between studies may, however, be related to the lower number of weekly days examined in our study (6 days) compared with the above-mentioned studies (7 days). The choice of 6 days was made because only 6 days elapsed between 2 matches during the most representative competition week. Future studies involving match and time motion analyses may help in assessing the effectiveness of the different TLs that could be needed to attain optimal performance in soccer (34,47). Vertical jump, sprint, and endurance running performance remained unchanged during the 9-week competitive period. Minor changes in physical fitness during the competitive season are consistent with the results obtained in male elite handball (19), soccer (1,30), and basketball players (21). It is not known why minor changes are observed in physical fitness in elite players, despite using an in-season conditioning program. The most likely explanation is that the training program lacked the intensity and/or the volume required to induce physiological adaptations. An alternative explanation could be related to some interference of endurance training with strength development in the legs. Some studies performed with elite team sport players (19,21), and recreational subjects (22) have found that simultaneous training for strength and endurance may reduce the capacity to develop strength, especially during prolonged training periods. These results agree with this study, in which significant inverse correlation was observed from the first to the ninth week between the individual values of accumulated time devoted to training and matches and individual changes in vertical jump performance (Figure 4A). This correlation was statistically significant despite the presence of 2 points appearing to be almost outliers, which worsen the degree of linear dependence between both variables. Furthermore, an inverse correlation was also observed during the intervention period
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between the individual values of accumulated sRPEmus and changes in sprint running velocity. It indicates that soccer players who devote more time to training and matches or experience a higher accumulated feeling of strain in the working muscles are more likely to produce major sprint running and vertical jump performance losses than those with less time devoted to training and matches or with a feeling of strain in the muscles. Although correlation does not imply causation, it is not unreasonable to suggest that the ability of lower extremity muscles to produce power and speed may be inhibited by the high volume of the predominantly aerobic type of training used during the competitive season and by repeatedly high levels of strain on the peripheral working muscles and joints. This observation is in accordance with a number of studies performed with elite basketball (21) and handball (19) players and further support the need for careful and significant attention to individual training programs in team sport players (19,46).
PRACTICAL APPLICATIONS This study demonstrates that average sRPEmus at the end of an official soccer match is very high and significantly greater than sRPEres. This suggests that at the end of a soccer match, professional players have a higher subjective perception of strain from their peripheral working muscles and joints than perceived tachycardia or breathing. This provides support to the suggestion that leg fatigue is the most prevalent factor toward the end of the match for players who play .70 minutes. Finally, lower extremity power and sprint velocity development may be interfered with by an excessive amount of total time devoted to training and matches, or by a strong feeling of strain from the peripheral working muscles and joints.
ACKNOWLEDGMENTS The authors thank C.A. Osasuna and the coaches of C.A. Osasuna B team for the opportunity to perform this investigation.
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47. Wrigley, R, Drust, B, Stratton, G, Scott, M, and Gregson, W. Quantification of the typical weekly in-season training load in elite junior soccer players. J Sports Sci 30: 1573–1580, 2012.
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AND
ESTEBAN M. GOROSTIAGA3
1
Department of Physical Education and Sport, Faculty of Physical Activity and Sport Science, University of the Basque Country, UPV/EHU, Vitoria-Gasteiz, Spain; 2Department of Physical Therapy, Zentrum Rehabilitation and Performance Center, Pamplona, Spain; and 3Studies, Research and Sport Medicine Center, Government of Navarre, Pamplona, Spain ABSTRACT
Los Arcos, A, Yanci, J, Mendiguchia, J, and Gorostiaga, EM. Rating of muscular and respiratory perceived exertion in professional soccer players. J Strength Cond Res 28(11): 3280–3288, 2014—This study investigated, in male professional players: (a) fluctuations in rating of local-muscular (sRPEmus) and central-respiratory (sRPEres) perceived exertion measured after the completion of each training and competitive session, over a 9-week competitive period and (b) the influence of quantitative assessment of different training and competition modes on changes in physical performance. sRPEres, sRPEmus, and heart rate were measured in 21 players in 847 individual training and competitive sessions. Training load was calculated by multiplying sRPEmus or sRPEres by the duration of the training or competition sessions. A test battery (vertical jump, sprint, and endurance running) was performed before and after the studied period. At the end of official matches, average sRPEmus was higher (7.4 6 0.6; p # 0.05) than sRPEres (6.4 6 1.3). Significant negative correlations were observed between the values of total training and competition time (r = 20.62; p , 0.01) or total added sRPEmus (r = 20.59; p # 0.05), and vertical jump or sprint running velocity changes, respectively. This suggests that sRPEmus should be considered the main fatigue rating during a soccer match. Training and competition volume may have negative effects on the muscle power performance gains of the legs.
KEY WORDS soccer, training, match, training load, physical performance
INTRODUCTION
A
ccurate assessment of the physiological stress imposed on the athletes, called physiological training load (TL) (17), is a key factor used to monitor and control the training and competition
Address correspondence to Javier Yanci, [email protected]. 28(11)/3280–3288 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
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process, to prevent under and over training, and to ensure that each athlete is in optimal condition for competition (25). This is particularly important in team sports, where individual differences in physiological responses to the imposed training and competition load occur (23,34). One of the most objective methods for quantifying TL in long duration effort is heart rate (HR) monitoring during training sessions (1,26). However, the routine recording of HR monitoring is only limited to scientific research and a few top professional teams (25), due to problems such as technical expertise, the time-consuming process of collecting HR data from all team players in every training session, the uncomfortable feeling of wearing the device during soccer practice, and the cost of several HR telemetric systems (25). Foster et al. (14–17) were the first to propose a subjective alternative method for evaluating TL in endurance and team sport athletes. This simple, valid, cheap, and reliable method, called “overall session rating of perceived exertion (sRPE),” represents the athlete’s own perception of training stress and gives a more holistic indication of the global physiological load because it is indicative of both physiological and psychological parameters (37). It is also intended to encourage players to view the training session as a whole (17). It calculates physiological TL by multiplying the individual overall sRPE, using a 0–10 scale as a measure of exercise intensity of the whole training session (16), by the duration of the session (in minutes). This product, named session rating of perceived exertion training load (sRPE-TL), represents the magnitude of physiological TL in arbitrary units (AUs), in a single number, and it seems to provide a valid and reliable measure of the physiological TL when both anaerobic and aerobic systems are appreciably activated, as is the case during soccer training and match play (2,25,44). Several descriptive studies performed over a few weeks with speed skaters (14), male basketball players (16,34), and young (1,25) professional soccer players (26,28) have described the mean most common weekly physiological TL using sRPE-TL. These descriptive studies have never provided evidence, however, of the utility of TL assessed by sRPE-TL over several weeks of training to predict or represent changes in the main physical performance characteristics of adult professional soccer players (1,8). This
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Journal of Strength and Conditioning Research assessment is of interest because a controlled research design to determine the best manipulation of TL to improve soccerspecific physical performance is lacking and could be useful to guide the training process (34). The above-mentioned studies measured an “overall” perceived exertion rating, which probably integrates a variety of information, including the many signals elicited from the peripheral working muscles and joints, the central cardiovascular and respiratory functions, and the central nervous system. Some authors (13,38) proposed differentiated ratings of perceived exertion in comparison with the overall measure, to provide a better explanation of the mechanisms by which the subjective perception of exertion is determined during physical work. They distinguished 3 ratings of perceived exertion (RPE), devoted to: (a) “local” or “muscular” (RPEmus, i.e., the feeling of strain in the working muscles), (b) “central” or “respiratory” (RPEres, i.e., perceived tachycardia, tachypnea, and even dyspnea), and (c) “overall” (RPE overall). To the best of our knowledge, there are no published studies that have dealt with local-muscular and central-respiratory perceptions during soccer training and competition sessions, nor published studies quantifying physiological TL that differentiate sRPEmus and sRPEres during whole training and competition sessions over several weeks in this population. The distinction between sRPEmus and sRPEres can be considerable in soccer because toward the end of a match, a muscle fatigue scenario (5,35,36,41) seems to coexist with only a submaximal involvement of the cardiovascular and respiratory system (75% of maximal oxygen uptake, 80–90% of maximal HR) (5,36,46). In this regard, the assessment of the physiological sRPEmus and sRPEres-TL, called sRPEmus-TL and sRPEres-TL, respectively, could result in a better understanding of the required TL needed to optimize the training process in team sports. The purposes of the study were therefore: (a) to investigate the training and competition fluctuations in sRPEmus, sRPEres, and TL monitored over a 9-week in-season competitive period in professional players and (b) to determine the influence of the quantitative assessment of different training and competition modes on changes in physical performance over the course of that competition period. One hypothesis was that sRPEmus and sRPEres would differentiate RPE during training and matches. It was also hypothesized that the quantitative assessment of different training variables could be related to changes in physical performance.
METHODS Experimental Approach to the Problem
The study was performed during the in-season competitive period (from September to May) in a 9-week period from October to December, and it began 9 weeks after the end of a 5-week preseason period. A global feeling of strain in the working muscle and the other central (respiratory), on global perceived tachycardia, tachypnea, and even dyspnea of the
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whole training session or match was solicited from each participant 10 minutes after completion of each training and competition session. Also, HR was recorded during training sessions. The participants were tested for anthropometrical variables and vertical jumping capacity, maximal sprint, and running endurance before and after the 9-week period using identical protocols, to determine the changes in physical performance over the course of that competitive period. Subjects
Twenty one Spanish male professional soccer players (age = 21.0 6 1.7 years; body height = 181.0 6 6.3 cm; body mass = 76.1 6 7.7 kg) in a third division team, made up of players belonging to the youth team of a professional elite first division team, participated in this study. Players usually performed 4–6 training sessions per week, plus 1 official match. Before the beginning of the study, written informed consent was obtained from all players. The participants and coach were informed about the experimental procedures and the possible risks and benefits of the project, which was approved before the start of the study by the local institutional review board for use by human participants, according to the Declaration of Helsinki. Procedures
Tests were performed after 1 day of minimal physical activity, on 1 day, in a fixed order and in the same facilities. Before the physical tests, each participant was subjected to anthropometrical measurements. After, vertical jump and sprint and endurance running tests were performed. The goalkeepers (n = 2) did not perform the endurance running test. Testing was integrated into weekly training schedules. The participants were familiarized with the testing protocol because they had been tested on several occasions in previous seasons for training prescription purposes with the same procedures. In a pilot study, the intertest reliability for measuring anthropometrical variables, together with several endurance indices, had been assessed on 2 trials, separated by 7 days, in a group of team sport players. The testretest intraclass correlations coefficients (ICCs) of the anthropometric and vertical jumping variables used in this study were .0.91 and the coefficients of variation (CV) ranged from 0.9 to 7.3%. Similarly, the ICC and CV for the velocity associated with a fixed submaximal blood lactate concentration were 0.94 and 2.2%, respectively. Jumping Test. On an indoor court, the participants did the jumping test after a standardized 15 minutes warm-up period. The participants were asked to perform a maximal countermovement vertical jump, on a jumping mat (Newtest OY, Oulu, Finland), with the hands fixed on the hips. The participants performed the jump from an extended leg position, down to 908 knee flexion, immediately followed by a subsequent concentric action for maximal height where the participants were instructed to land on the contact platform in a position similar to that of the take-off. The jumping VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Perceived Exertion in Soccer
TABLE 1. Anthropometric and physical characteristics values at the beginning (pretest) and at the end (posttest) of the 9-week competitive period.* Variables Body mass (kg) CMJ (cm) SPR5 (s) SPR15 (s) Lac10 min (mmol$L21) Lac25 min (mmol$L21)
n
Pretest
21 18 16 16 16 16
76.1 43.3 0.96 2.28 2.89 3.16
6 6 6 6 6 6
7.7 5.0 0.03 0.07 0.72 0.73
Postest
Change (%)
6 6 6 6 6 6
0.52 1.61 0.00 0.00 1.38 0.94
76.5 42.6 0.96 2.28 2.85 3.13
7.4 4.5 0.04 0.07 0.49 0.71
*CMJ = countermovement jump; SPR5 = 5-m sprint time; SPR15 = 15-m sprint time; Lac10 min = blood lactate concentration value at 10 minutes during the endurance running test; Lac25 min = blood lactate concentration value at 25 minutes during the endurance running test.
height was calculated from the flight time. Two sets of 3 maximal jumps were recorded, interspersed with approximately 10 seconds rest between jumps and 90 seconds rest between sets. The best reading was used for further analysis. Maximal Sprint and Endurance Running Test. Ten minutes after completion of the jumping test and after a standardized warm-up period for sprint running, participants undertook a sprint running test consisting of 3 maximal sprints of 15 m on an indoor court, with 90 seconds rest between each sprint. Fifteen meter was chosen because is the average sprint length observed during official matches in elite soccer players (7). During the 90-second recovery period, the participants walked back to the starting line. The recording of running time was done using photocell gates (Newtest OY, Oulu, Finland) placed 0.4 m above the ground with an accuracy of 0.001 seconds. The participants commenced the sprint when ready from a standing start, 0.5 m behind the start and the sprint start was self-initiated. Stance for the start was consistent for each participant. The time was automatically activated as the participant passed the first gate at the 0-m mark, and split times were recorded at 5 and 15 m. The lowest time was selected for further analysis. The endurance running test was performed 10 minutes after the end of the sprint running test on an artificial outdoor grass soccer court (1003 50 m). Each participant performed a 2-stage constant submaximal velocity running test with a 2-minute rest between each run. Time for the first stage was 10 minutes, and for the second stage, 15 minutes. For each participant, the running velocity corresponded to the individual value of the velocity associated with a blood lactate concentration of 3 mmol·L21, obtained by extrapolation during a previous preliminary 4-stage submaximal discontinuous progressive running test, explained in detail elsewhere (20). To assure a constant velocity, participants were instructed to run at an even pace through an audio signal connected to a preprogrammed computer. Immediately after each exercise stage, and after cleaning and puncturing,
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a 5-ml sample of whole blood was automatically aspirated from a hyperemized earlobe into a single-use enzyme-coated electrode test strip. Lactate concentration was determined through amperometric measurement, and the result displayed in 60 seconds (Lactate Pro LT-1710; Arkray KDK Corporation, Shiga, Japan). In terms of reliability, the manufacturers report a CV of 3.2 and 2.6% with lactate standards of 2 and 11 mmol$L21 respectively. Although the velocities of this endurance constant velocity running test differed between participants, they were the same in each participant before and after the 9-week period (11.9 6 0.4 km·h21). Our criterion of endurance capacity was the blood lactate concentration elicited during submaximal exercise at a given velocity _ O2max because it has been shown to be more sensitive than V in the physiological outcome in soccer (26). Training and Competition Data Analysis. Training session duration ranged from 60 to 85 minutes. The heaviest aerobic training exercise was usually completed 4 days before the match day (M-4) and consisted of continuous running or interval training. Three days before the match (M-3), 20 minutes were generally dedicated to speed development or to heavy resistance training consisting mainly of sprint, plyometric, half-squat, and jumping exercises. The rest of the training usually consisted of various skill activities at different intensities, small-sided games with individual technical and tactical objectives, offensive and defensive strategy, and 3 3 7 minutes of continuous play. Each participant was monitored in every training and competition session by one of the researchers, who was the physical conditioning coach of the team. Diet or lifestyles were not controlled during the course of the study, although some of the players were encouraged to maintain body weight. Determination of Physiological Training Load. Approximately 10 minutes after the completion of each training session or match, a rating of the difficulty of the whole training session or match was solicited from each participant, except the
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of getting an uncomplicated response that reflects the athlete’s global impression of the workout (15). We delayed securing the session sRPE rating for 10 minutes so that particularly difficult or particularly easy segments toward the end of the exercise bout would not influence the participant’s rating (14) too much. The participants had to differentiate between 2 types of RPE: 1 local (leg, muscular), regarding the global feeling of strain in the working muscle, named sRPEmus, and the other cenFigure 1. Average time corresponding to 3 HR zones (,70, 70–90, and .90% of HRmax), during the 4 training days preceding the competition day (match, M) at the most typical weekly microcycles (match on Sundays and the tral (chest, respiratory), on following Saturdays). HR was collected for 167 individual training sessions in 19 players. The number of HR global perceived tachycardia, recordings per player ranged from 36 to 49. M-4: n = 16, 43 occasions; M-3: n = 16, 38 occasions; M-2: n = 16, tachypnea, and even dyspnea, 47 occasions; M-1: n = 16, 33 occasions. HR = heart rate; HRmax = maximum heart rate. named sRPEres (13,38). Each player completed the RPE scale without the presence of goalkeepers, using the 0–10 point Borg’s category RPE scale other players, and they could not see the values of other (9), modified by Foster et al. (14,17). A Spanish translation of participants. Players were allowed to mark a plus sign (interpreted as 0.5 point) alongside the integer value if they this scale was used. We explained to the participant that we wished (16). Participants were familiarized with the use of wanted a global rating of the entire training or competition the 10-point scale before the data collection for this study bouts, using whatever cues they felt to be appropriate. The athlete responded to 2 simple questions, always asked in this over a month. The duration of a training or match session order—How intense was your session on your chest? and was recorded for each player from the start to the end of the How intense was your session on your legs?—With the aim session, including recovery periods but excluding time devoted to stretching exercises during training sessions and time spent on warm-up and half-time during match sessions. An exercise score, which has been called the session training or competition “load,” was computed by multiplying the duration of the training or competition session by the sRPEres or sRPEmus, as described by Foster et al. (16,17). The session training or competition loads were named sRPEres-TL or sRPEmus-TL, and measured in AU. Daily and weekly sRPEmus-TL and sRPEres-TL were calculated from the sum of all training and competition sessions performed in a day and week, respectively Figure 2. Average (6SD) sRPEres and sRPEmus values after the match depending on the minutes played per match. *p # 0.05: significant differences between sRPEres and sRPEmus. #p , 0.01: significant differences (14,25). Total weekly sRPEmusbetween ,20 or 20–45 and .70 in sRPEres. ^p , 0.01: significant differences between ,20 or 20–45 and TL and sRPEres-TL were taken .70 in sRPEmus; ,20 (n = 9 players; 18 occasions), 20–45 (n = 11 players; 17 occasions), and .70 (n = 15 as an average of the 9 weekly players; 78 occasions). sRPE = session rating of perceived exertion. training cycles. VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Perceived Exertion in Soccer analyzed. The physiological intensity of all training sessions were indicated by both mean absolute (beats per minute) and relative values (i.e., the corresponding percentage of maximum heart rate; % HRmax) of HR. The time spent within specific HR zones (.90, 70–90, and ,70% HRmax) was also measured. Maximum heart rate was estimated to be 10% higher than the average HR recorded during the last 10 minutes of the endurance running test (29,45). To validate the sRPEres and sRPEmus to monitor training Figure 3. Representation of the daily training and competition load determined using mean sRPEres-TL and and competition loads in team sRPEmus-TL during the more representative competitive week (n = 12). *p , 0.01 significant differences between sports, we examined the inditraining days in sRPEres-TL or sRPEmus-TL. #p , 0.01 significant differences between trainings and match in sRPEres-TL or sRPEmus-TL. M-4: n = 19, 77 occasions; M-3: n = 19, 78 occasions; M-2: n = 19, 76 occasions; vidual relationships between M-1: n = 19, 72 occasions; match: n = 12 players, 26 occasions. AU = arbitrary unit; sRPE = session rating of sRPE and an objective measure perceived exertion; TL = training load. of internal load (HR). To do this, the RPE TLs for each training session or match The players, except the goalkeepers, wore HR monitors (sRPEres-TL and sRPEmus-TL) were calculated as previously (Polar Team Sport System; Polar Electro Oy, Kempele, Finland) reported in this study. In addition, the individual product of the during all the training sessions as an objective reference method accumulated training duration in 5 HR zones by a coefficient for quantifying each training session. Heart rate was recorded at relative to each zone (from 50 to 60% of HRmax = 1 to 90– 5-second intervals. No HR was recorded during matches 100% of HRmax = 5) was computed and summated for each because of the prohibition of wearing HR monitors and belts training session, as proposed by Edwards (12). The HR-based during official competitive matches. All players were regularly TL scores (HR-TL) and the sRPEres and sRPEmus-TL scores asked to check their HR monitors during each training session. (sRPEres-TL and sRPEmus-TL, respectively) were calculated After each training session, HR data were downloaded to from an average of 27 6 4.5 training sessions per player. a portable PC using the specific software and exported and Regression analysis showed that the individual correlations
Figure 4. A) Relationship between the values of total accumulated time devoted to (training + match), and the individual relative changes of vertical jumping performance (in percentage of the initial values), during the 9-week experimental period. B) Relationship between the individual values of total added (training + match) sRPEmus and the relative changes in 15-m sprint running velocity (in percentage of the initial values), during the 9-week experimental period. CMJ = countermovement jump.
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between sRPEres-TL and HR-TL were all significant (p , 0.01), from r = 0.67 to r = 0.91 (average: 0.87 6 0.06). Similarly, individual correlations between sRPEmus-TL and HR-L were all significant (p , 0.01) from r = 0.67 to r = 0.91 (average, 0.84 6 0.07). The magnitude of the individual correlations is in agreement with that reported by previous investigators measuring overall sRPE-TL and HR-TL values in team sports players (16,25,44) during practice sessions. This suggests that the sRPEres-L and the sRPEmus-TL methods provide approximately the same information as the HR-based method, and they could be considered a good tool to monitor internal TL in team sports such as soccer (14,25).
following Saturday, and this was considered the most typical weekly microcycle. At this typical microcycle, the mean total time spent by 16 players in 3 HR zones (,70, 70–90, and .90% of HRmax) during the 4 training days preceding a match day is shown in Figure 1. On these training days, the global relative contributions of each HR zones were 50.2 6 19.9% (,70% HRmax), 40.5 6 16.0% (70–90% HRmax), and 9.3 6 10.0% (.90% HRmax). Three players were not included in the HR analysis because their recorded session number was low (,4) due to HR recording problems or low attendance at the training sessions in these typical weekly microcycles.
Statistical Analyses
Session Rating of Perceived Exertion Scores After Matches
Standard statistical methods were used for the calculation of the mean values and SDs. Data were screened for normality of distribution and homogeneity of variances using a Shapiro-Wilk normality test. The changes in physical performance over the course of the 9-week experimental period were compared using Student’s paired t test. A 2 3 3 (playing match time) analysis of variance condition (condition 3 time) with repeated measures was used to determine mean differences. Significant differences between mean values were identified using a Bonferroni’s post hoc test. Pearson’s product-moment correlations coefficients (r) were used to determine the relationships between changes in fitness parameters and physiological load values. The following scale of magnitudes proposed by Hopkins (24) was used to interpret the correlation coefficients: ,0.1 = trivial; 0.10–0.29 = small; 0.30–0.49 = moderate; 0.50–0.69 = large; 0.70–0.90 = very large; and .0.90 = nearly perfect. Statistical significance was set at p # 0.05. Data analysis was performed using the Statistical Package for Social Sciences (version 18.0 for Windows; SPSS Inc., Chicago, IL, USA).
Since 3 substitutions are allowed in a soccer match, the number of minutes played at each match varied widely within and between subjects. Thus, there were 9 subjects who played less than 20 minutes per match on 18 occasions, 11 who played between 20 and 45 minutes per match on 17 times, and 15 who played more than 70 minutes on 78 occasions. A repeated-measures analysis of variance indicated that the pattern of sRPEres and sRPEmus response differed (p , 0.01) as the match progresses (Figure 2). Thus, when players played less than 20 minutes per match, average sRPEmus (;3.3) was lower (p , 0.01) than average sRPEres (;4.4), whereas when they played between 20 and 45 minutes per match, average sRPEmus and sRPEres were similar (;4.3–4.7). However, when the players played more than 70 minutes per match, average sRPEmus at the end of the game was very high (;7.4) and significantly higher (p # 0.05) than sRPEres (;6.4).
RESULTS Anthropometric Characteristics and Changes in Physical Performance
The data on anthropometric characteristics and physical performance values at the beginning and at the end of the studied period are presented in Table 1. No changes occurred in body mass, vertical jumping performance, and sprint running time during this period. Before the experimental period, average blood lactate concentration remained stable (;3 mmol$L21) between 10 and 25 minutes at the constant velocity endurance running test performed. No changes in mean blood lactate concentration were observed at this same absolute running velocity during the experimental period. Times Spent at Training and in Heart Rate Zones
During the experimental period, each player performed an average of 40 training sessions (4.8 training sessions per week), for a total average duration of 2,848 minutes. The team played 9 matches during the experimental most frequent match sequence (4 weeks) from Sunday to the
Session Rating of Perceived Exertion Training Load Scores at Training and Competition
sRPEres and sRPEmus were collected for 847 individual training sessions and for 120 individual matches. Figure 3 shows the pattern of the average sRPEres-TL and sRPEmus-TL profiles during the more typical weekly microcycle that comprised 1 match on day “M-6” and the following match on day “M” (from Sunday to Saturday). For descriptive purposes, all data were used for the training sessions but only data of players playing more than 70 minutes (n = 12) were used for the match score. A significant main effect over time was observed (p , 0.01). We did not observe a main effect for condition (sRPEres-TL vs. sRPEmus-TL) or a condition 3 time interaction (p . 0.05). Mean comparisons for training days were all significantly different (p , 0.01). The highest TL scores were observed at (M-3), and the lowest values were observed at (M-1), whereas at M-4 and M-2, the score values were between those observed in M-3 and M-1. The highest scores of the week were observed on the match day in the players playing .70 minutes per game, and they were approximately 100% greater than those observed during the hardest training day. No differences were observed in a day between sRPEres-TL and sRPEmus-TL scores. Total (training + match) average VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Perceived Exertion in Soccer weekly sRPEres-TL and sRPEmus-TL were 1515 6 134 and 1576 6 147 AU, respectively. Relationships Between Quantitative Assessment of Training and Competition and Physical Characteristic Changes
Large significant inverse linear correlations were observed during the study between the accumulated values of total added (training + match) times and relative changes in vertical jump performance (r = 20.62; p , 0.01; n = 18) (Figure 4A). Similarly, large significant inverse correlations were observed between the total added (training + match) sRPEmus values and the individual relative changes in 15-m sprint running velocity (r = 20.59; p # 0.05; n = 15) (Figure 4B).
DISCUSSION One of the main findings of this study was that players playing more than 70 minutes per match had a very high average sRPEmus at the end of the game (;7.4), significantly higher than sRPEres (;6.4). Higher sRPEmus than sRPEres values at the end of exhausting exercise is in agreement with exhausting cycling studies performed in healthy moderately trained young (18) and middle-aged (10) men. This suggests that at the end of a soccer match, professional players have a higher subjective perception of strain from their peripheral working muscles and joints than from their central cardiovascular and respiratory functions. From the existing data, it cannot be determined whether sRPEmus is linked directly with muscular fatigue or it can also be attributed, at least in part, to additional inputs from other peripheral organs and from the central nervous system. Nevertheless, the very high feeling of strain in the working muscles toward the end of a professional soccer match may be related to some physiological changes occurring inside the muscle. Several studies on amateur and professional (5,32,42) soccer players have found abrupt alterations in muscle cells at the end of official or unofficial matches, such as a reduction of muscle glycogen stores (5,42), with nearly half of the muscle fibers being completely or almost empty of glycogen (31,32), a very high rate of lactate production and muscle acidosis during periods of high intensity in a match (5,31,32), deterioration of muscle sarcoplasmic reticulum function (33), accumulation of potassium in the muscle interstitium (6), low or depleted muscle creatine phosphate concentrations in individual muscle fibers (31), and reduced muscle ATP stores in individual fibers (5,32). Furthermore, increases in the expression of reliable markers for muscle cell, muscle cell disruption, or oxidative damage occur at the end of soccer matches and are reflected by elevated levels of blood ammonia/ammonium (NH3) (5,32), uric acid (4,5), malondialdehyde (4), protein carbonyls (27), myoglobin (4,33), lactate dehydrogenase (27), and creatine kinase (4,27,40). Bangsbo (5) has suggested that these muscular and blood changes may show a fatigue scenario in which the recruitment of the fast-twitch muscle fibers to generate force decreases during a match because they become progressively fatigued. Assuming that muscle
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force, velocity, and power production are indicators of local muscle status (43), this muscle fatigue scenario is corroborated by a significant decline in the amount of high-intensity running (35), sprinting ability (4,27,32,41) and the forcegenerating capacity of knee extensor (4,27), and flexor (4) muscles observed toward the end of a match in top youth (41), amateur (4,32), and professional soccer players (27). The observation that the substitutes who came on in the second half perform more high-intensity running and more sprinting than players playing the entire game (35) supports the notion that the lower match intensity and physical performance during the last phase of a match is caused by match-induced fatigue. This provides support to the suggestion that leg fatigue is most dominant factor toward the end of a match for players who play more than 70 minutes (39). Although sRPEmus in the players playing more than 70 minutes per match was strong and higher than sRPEres, the pattern of sRPEres and sRPEmus response differed as the match progresses. Hence, when players played less than 20 minutes, average sRPEmus was “moderate” (;3.3) and lower than average sRPEres (;4.4), whereas when they played between 20 and 45 minutes, average sRPEmus and sRPEres were similar (;4.3–4.7), between “somewhat strong” and “strong.” This indicates that sRPEres increases less abruptly than sRPEmus as the match progresses. It has been assumed that oxygen uptake and HR are closely related to central factors (cardiac and pulmonary output) (43), and sRPEres is a good correlate for central cardiovascular and respiratory strain perception (11). The lower increase in sRPEres observed along the game could be related to the fact that relative work intensity (a central cardiorespiratory index) is only submaximal, around 70–75% V_ O2max or between 80 and 90% of HRmax (46) during the first half, and even declines slightly during the second half of a soccer match (5,33,36,40). The magnitude of these central changes is much lower than the above-mentioned changes that occur within the muscle cells as the match progresses. It is suggested that in soccer matches longer than 70 minutes, sRPEmus is more sensitive than sRPEres in detecting fatigue. A clear training and match load profile was observed during the most representative week, which included 1 competitive official match. Training load built up to a midweek peak, and this was followed by subsequent sessions of less activity as a taper for the weekend match. This weekly profile is similar to that previously observed in professional basketball players and in young (25,47) and professional soccer players (5,26,28) playing once a week. The tapering strategy used during the 2 days preceding the match may be linked to the need to provide adequate time to recover before the next match, and it has been reported to be most effective in inducing positive effects on performance in endurance sports (34). The match sRPEres-TL and sRPEmus-TL values (;625–650 AU) of the players playing more than 70 minutes per match (Figure 2) is consistent with the overall sRPE-TL observed in young (25) and
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Journal of Strength and Conditioning Research professional (26) soccer players and mostly represents the main TL of the week. However, the total (training and match) accumulated weekly sRPEres-TL or sRPEmus-TL values in our study (;1.500–1550 AU) were 25–60% lower than the accumulated weekly overall sRPE-TL (;2.100– 3.900 AU) previously reported in young (1,25,47), and professional adult (3,26) soccer players in a typical in-season week with 1 match to play. Besides, in these 3 studies, there was at least 1 weekly training session in which the overall sRPE-TL was similar or higher in magnitude to the one observed during the match, whereas in our study, the highest training sRPEres-TL or sRPEmus-TL values were 50% lower than the corresponding match sRPE-TL values. It is difficult to compare the results of these studies because they can differ markedly in a number of factors, including times of measuring sRPE (10–30 minutes after the end of the session), type of sRPE recorded (overall or differentiated RPE), excluded activities during time recording (e.g., warm-up, stretching time, etc.) and influences of instruction, experimental design, rating behavior, cultural differences, and context effects (11). The main explanation for the observed differences between studies may, however, be related to the lower number of weekly days examined in our study (6 days) compared with the above-mentioned studies (7 days). The choice of 6 days was made because only 6 days elapsed between 2 matches during the most representative competition week. Future studies involving match and time motion analyses may help in assessing the effectiveness of the different TLs that could be needed to attain optimal performance in soccer (34,47). Vertical jump, sprint, and endurance running performance remained unchanged during the 9-week competitive period. Minor changes in physical fitness during the competitive season are consistent with the results obtained in male elite handball (19), soccer (1,30), and basketball players (21). It is not known why minor changes are observed in physical fitness in elite players, despite using an in-season conditioning program. The most likely explanation is that the training program lacked the intensity and/or the volume required to induce physiological adaptations. An alternative explanation could be related to some interference of endurance training with strength development in the legs. Some studies performed with elite team sport players (19,21), and recreational subjects (22) have found that simultaneous training for strength and endurance may reduce the capacity to develop strength, especially during prolonged training periods. These results agree with this study, in which significant inverse correlation was observed from the first to the ninth week between the individual values of accumulated time devoted to training and matches and individual changes in vertical jump performance (Figure 4A). This correlation was statistically significant despite the presence of 2 points appearing to be almost outliers, which worsen the degree of linear dependence between both variables. Furthermore, an inverse correlation was also observed during the intervention period
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between the individual values of accumulated sRPEmus and changes in sprint running velocity. It indicates that soccer players who devote more time to training and matches or experience a higher accumulated feeling of strain in the working muscles are more likely to produce major sprint running and vertical jump performance losses than those with less time devoted to training and matches or with a feeling of strain in the muscles. Although correlation does not imply causation, it is not unreasonable to suggest that the ability of lower extremity muscles to produce power and speed may be inhibited by the high volume of the predominantly aerobic type of training used during the competitive season and by repeatedly high levels of strain on the peripheral working muscles and joints. This observation is in accordance with a number of studies performed with elite basketball (21) and handball (19) players and further support the need for careful and significant attention to individual training programs in team sport players (19,46).
PRACTICAL APPLICATIONS This study demonstrates that average sRPEmus at the end of an official soccer match is very high and significantly greater than sRPEres. This suggests that at the end of a soccer match, professional players have a higher subjective perception of strain from their peripheral working muscles and joints than perceived tachycardia or breathing. This provides support to the suggestion that leg fatigue is the most prevalent factor toward the end of the match for players who play .70 minutes. Finally, lower extremity power and sprint velocity development may be interfered with by an excessive amount of total time devoted to training and matches, or by a strong feeling of strain from the peripheral working muscles and joints.
ACKNOWLEDGMENTS The authors thank C.A. Osasuna and the coaches of C.A. Osasuna B team for the opportunity to perform this investigation.
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