International Journal of Sports Physiology and Performance, 2016, 11, 301 -304 http://dx.doi.org/10.1123/ijspp.2015-0270 © 2016 Human Kinetics, Inc.
ORIGINAL INVESTIGATION
Respiratory and Muscular Perceived Exertion During Official Games in Professional Soccer Players Asier Los Arcos, Alberto Méndez-Villanueva, Javier Yanci, and Raúl Martínez-Santos Purpose: The aim of this study was to assess the respiratory and muscular session ratings of perceived exertion (PE) after official soccer matches over an extended period of time (ie, 2 competition seasons) in relation to playing time (>20, 20–45, 45–70, and >70 min) and to determine the between-matches variability of both scores in young professional soccer players. Methods: Forty players belonging to the same reserve team of a Spanish La Liga club participated in this study. Respiratory and muscular PE were collected 10 min after every game. A total of 841 individual PE ratings were undertaken on outfield players. Results: The differences between match respiratory and muscular load differ depending on the playing time, the respiratory PE being greater for the players that competed less than 45 min (effect size = –0.45 ± 0.45 for the 20- to 45-min group) and the muscular PE greater for players that played more than 45 min (effect size = 0.23 ± 0.30, for the 45- to 70-min group). Match-to-match PE variability was considerable (CV = 14–54%) for all levels of participation, but it was lower the longer the players participated. Conclusions: Playing time influenced the relative exertion that players’ respiratory and leg musculature were exposed to during a game, suggesting that differential PE scores might provide a more accurate evaluation of match-imposed internal load. However, the small-magnitude differences between respiratory and muscular session ratings of PE observed in the current study might question the practical relevance of assessing both scores. Keywords: football, soccer match, RPE, training load Information about the training load (TL) imposed on a player after a soccer practice can be obtained by different means such as the analysis of the heart rate,1–5 running demands,6,7 and perceived exertion (PE).2,8–12 However, the quantification of the workload arising from the competition games is more difficult due to the prohibition of wearing heart-rate and/or GPS devices during official games and because only a few teams can use sophisticated computerized tracking systems to quantify the running demands. Taking into account that the match typically represents the highest TL of the week,2,9,13,14 its quantification appears relevant. The session rating of perceived exertion (sRPE) proposed by Foster et al15 to evaluate the internal TL in team sports has been previously used in soccer.2,9,10,12,16 The rating of perceived exertion (RPE) provides a simple, noninvasive, inexpensive, and valid method for assessing exercise intensity during the physical work17,18 or the hardness of the training session.15,19 The subjective perception of the effort integrates the sensations from the organs of circulation and respiration, from the muscles, the skin, or the joints, as well as the perception of effort, fatigue, strain exertion, heat, or pain.20 However, this gestalt could represent an oversimplification of the psychophysiological construct, making it insufficient to capture the whole range of exercise-related perceptual sensations.21 For this reason, various researchers have proposed the deconstruction of PE, differentiating, at least, between respiratory and muscular efforts.22,23 This method has been proposed as valid as very large
Los Arcos is with the School of Teaching, and Yanci and Martínez-Santos, the Faculty of Physical Activity and Sports Science, University of the Basque Country, Vitoria-Gasteiz, Spain. Méndez-Villanueva is with ASPIRE Academy for Sports Excellence, Doha, Qatar. Address author correspondence to Asier Los Arcos at
[email protected].
individual correlations have been obtained between respiratory and muscular perceived effort TL and heart-rate-derived measures of exercise intensity/load in soccer.2 Moreover, it has been recently suggested in team sports that differential PE scores can improve the precision in exertion scores, providing, in turn, a more accurate evaluation of match-imposed internal load.2,16,24 Two studies conducted with young professional soccer players have described substantial dose-response associations between perceived TL and changes in some physical-fitness variables after the independent assessment of respiratory and muscular PE.2,11 Therefore, the collection of training and match differential PEs can be a useful tool to better quantify TL in soccer. Professional soccer2,16 and Australian football players24 declare a greater PE in the leg muscles in comparison with the respiratory PE using both the Foster 0-to-10 scale15 and the centimax scale (CR100).25 Specifically, soccer players rated the match as “very hard” and the muscular sRPE (sRPEmus) (6.9–7.4) was greater than the respiratory sRPE (sRPEres) (6.4–6.6) after playing a whole official game16 or >70 minutes.2 That is, differentiated perceived TL (PE multiplied by match duration in minutes) was around 630 arbitrary units (AU), which was similar to the overall perceived TL quantified in young (17.6 ± .7 y) Italian soccer players (625 ± 60 AU) after playing >80 minutes9 but considerably lower than the overall perceived TL (759 ± 51 AU) accumulated by youth English soccer players (eg, U18) after playing a whole official game.12 However, at best, these studies analyzed less than 24 matches.2,9,12,16 Moreover, little is known about substitute players’ sRPE and perceived TL.2 In addition, the PE match-to-match variability along the season has not been described yet. Therefore, the aim of this study was to assess the sRPE after official soccer matches over an extended period of time (ie, 2 competition seasons) in relation to the minutes played and to determine the between-matches variability of PE in young professional soccer players. 301
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Methods Player and Match Data Match PE data were collected from 40 young professional soccer players belonging to the same reserve team of a first-division Spanish club and competing in the Spanish 2nd B division championship during the 2011–12 and 2012–13 seasons. The study was conducted according to the Declaration of Helsinki (2013) and was approved by the local ethics committee.
Data Collection and Analysis During the data collection, players trained 4 to 6 times a week and played an official match per week in the weekend (Saturday or Sunday) from September to May. Exceptionally, an official match on Wednesday and 2 additional friendly matches were played during this competition period in each season. The participants that played lesser minutes (substitutes) typically performed individual physical practice during match day to increase their weekly load. Ten minutes after every official match11 and using the Foster 0-to-10 scale,15 soccer players were asked by the same person (ie, fitness coach) on all occasions to rate their perceived level of exertion separately for respiratory and leg-musculature effort: respiratory perceived exertion (sRPEres) and muscular perceived exertion (sRPEmus).2,11 Players responded to 2 simple questions in a unique evaluation sheet always asked in this order: How hard was your session on your chest? How hard was your session on your legs? Players were allowed to mark a plus sign (interpreted as 0.5 point) alongside the integer value.2,8,11 Each player completed the 0-to-10 scale randomly without the presence of other players and could not see the values of other participants. All players were familiarized with this method during preseason trainings and friendly matches (6 wk). The playing match time was recorded for each player. The match duration excluded the warm-up and halftime rest.2,11 First, we described sRPEres and sRPEmus for the entire match played, comparing both ratings and analyzing the magnitude of the variability between matches. Then, players were assigned to 1 of 4 participation intervals—>70 minutes, £70 to >45 minutes, £45 to >20 minutes, and £20 minutes—to determine the influence of playing time on both respiratory and muscular sRPE. Later, sRPEres and sRPEmus were compared for each match interval, and the variability between matches was calculated for each group.
unlikely; 25% to 75%, possible; 75% to 95%, likely; 95% to 99%, very likely; >99%, almost certainly. If the chance of having higher or lower values than the smallest worthwhile difference were both >5%, the true difference was assessed as unclear. Data analysis was performed using a modified statistical Excel spreadsheet29 and the Statistical Package for Social Sciences (version 20.0 for Windows, SPSS Inc, Chicago, IL, USA). Statistical significance was set at P < .05.
Results A total of 841 individual PE ratings were undertaken on outfield players (goalkeepers were excluded) with a median of 23 games per player: entire match played (players = 30, occurrences = 463), >70 minutes (players = 31, occurrences = 571, mean playing time = 91.7 ± 6.4 min), £70 to >45 minutes (players = 24, occurrences = 88, mean playing time = 58.2 ± 7.2 min), £45 to >20 minutes (players = 26, occurrences = 95, mean playing time = 31.1 ± 6.9 min), and £20 minutes (players = 23, occurrences = 87, mean playing time = 11.5 ± 5.1 min). Players rated the entire official match (ie, >90 min) as “very hard,” sRPEres = 6.7 ± 1.3 and sRPEmus = 6.9 ± 1.6, being respiratory and muscular perceived TL of 630 ± 126 and 655 ± 150 AU, respectively. The practical differences between match sRPEmus and sRPEres were trivial (sRPEmus > sRPEres; ES = –0.17 ± 0.63, unclear 17/39/46). Match-to-match variabilities in sRPE for players that played the entire game (ie, >90 min) were 18.2% ± 6.2% and 19.4% ± 9.3% for sRPEres and sRPEmus, respectively. After assigning players to 1 of the 4 participation intervals (ie, 70 min) the players’ declared sRPEs (ie, respiratory and muscular) were 70 minutes, sRPEres = 6.7 ± 1.4 and sRPEmus = 7.0 ± 1.6 (Figure 1). The differences between sRPEres and sRPEmus for each playing-time group were trivial for the 70 min, 45–70 min, 20–45 min,
