Elite Female Soccer Players Perform More High-Intensity Running When Playing in International Games Compared With Domestic League Games : The Journal of Strength & Conditioning Research

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Original Research

Elite Female Soccer Players Perform More High-Intensity Running When Playing in International Games Compared With Domestic League Games

Andersson, Helena Å1; Randers, Morten B2; Heiner-Møller, Anja2; Krustrup, Peter2; Mohr, Magni2

Author Information
Journal of Strength and Conditioning Research 24(4):p 912-919, April 2010. | DOI: 10.1519/JSC.0b013e3181d09f21
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Abstract

Introduction

The use of time-motion analysis to evaluate the movement pattern and physical aspects of soccer games have extensively been reported in elite male players (4,5,15,18,20) and have recently received more attention in elite female players (6,9,13,14). It has been reported that a higher workload is performed by players at higher competition level games compared with players at moderate levels in both male and female players (6,14,15). In the study by Mohr et al. (15), we compared the work performed during games in top-class vs. high-level female players. We observed that the top-class players covered more distance at high intensities compared with the high-level players, which could partly be explained by a superior fitness level in the top-class players (15). In addition to the fitness level, it has also been shown that the opponent has an impact on exercise intensity and the fatigue development during games (19). Thus, by investigating whether international soccer games are more physically demanding than domestic league games for the same elite female players, within a short time period so that the physical fitness level is the same, we are able to observe the influence of the game level on movement pattern more precisely.

It has been shown that elite players of both genders fatigue temporarily during a game and toward the end of a game (11,12,15,16,18,20). If the workload is higher during an international compared with a domestic league game, this is likely to affect the fatigue patterns during the international game. Rampinini et al. (19) demonstrated that high exercise intensity in the first half has a negative impact on the intensity in the second half. The ability to sustain high exercise intensity toward the end of an international game is important for the game outcome because most goals are usually scored during this game interval (21). However, no study has yet compared the fatigue development in domestic vs. international games for the same players. For the national team coaches, and for the players, it would be valuable information to know possible differences in physical demands in an international game in comparison to a domestic league game.

To our knowledge, only one attempt has previously been carried out to clarify if the exercise intensity differs between levels of games for the same players (6). The movement pattern in small-sided games was compared with domestic friendly games and international games in Australian female players (6). However, some of the domestic league games were friendly games and were played vs. youth male players, which is likely to effect the intensity of the game. Also, it is unclear to what degree the same player was compared in each of the game types, as they state “if one player was unavailable for filming, a player from the same position was filmed” (6). Because there are large individual variations in exercise intensity between players even in the same playing position (16), this is likely to have affected their findings. Thus, there is need for more information regarding the physical demands in international compared with domestic games played by the same player.

Thus, the aim of this study was to compare the exercise intensity and fatigue development in elite female players during international compared with domestic league games. To examine this, we analyzed the movement pattern and heart rate (HR) response for the same elite female player during competitive international and domestic league games. Additionally, we aimed to compare the exercise intensity between different playing positions during the games.

Methods

Experimental Approach to the Problem

To study exercise intensity and the fatigue development during international games and domestic league games, we performed video-based time-motion analyses for the same players in 1-3 international games and 1-3 domestic league games. In addition, we compared the HR response between international and domestic league games by continuous HR recordings throughout each of the games.

Subjects

Seventeen top-class female women soccer players from the national team in Sweden and Denmark were included in the study (9 defenders, 5 midfielders, and 3 forwards). Their age, height, weight, and mean peak HR were 27 ± 1 years, 168.2 ± 1.5 cm, 61.0 ± 1.4 kg, and 191 ± 2 b·min−1, respectively. For inclusion in the study, the players had to be part of their respective countries' national team for a minimum of 5 years and were all players regularly starting the games (i.e., not substitutes). The players all played in a top club team in the Swedish or Danish highest division and were therefore eligible to participate in the UEFA Women's Cup tournament. The players were informed of the experimental procedures and possible discomforts associated with the study before given their written informed consent to participate. The study was conducted according to the Declaration of Helsinki and approved by the Ethics Committee of the Karolinska Institute, Sweden.

Study Design and Procedure

The study was designed to compare the exercise intensity and fatigue development during domestic league (DOM) vs. international (INT) games. The exercise intensity was measured by using time-motion analysis of locomotor activities and measurement of the players' HR during the games. The fatigue development was determined using a method previously described by Mohr et al. (16), where the time-motion analysis is divided into smaller time fractions during the game, such as 15- and 5-minute periods. For the time-motion analysis, each player was observed individually by video filming in up to 3 domestic league games and 3 international games. All games were competitive, and the game's outcome was important to the respective team. The international games were either games with the respective player's national team or UEFA Women's cup games with the players' club team, not both. The domestic games were games with the respective players' club team played against teams in the national leagues. Importantly, the players played in the same position on the field during both DOM and INT (9 defenders, 5 central midfielders, and 3 forwards). In total, 54 games have been included in the analyses. Each player has been analyzed in 1-3 INT and DOM games (10 players in 1 game and 7 players in 2-3 games for each game type). The INT and DOM games were filmed with less than a month apart for each player so that the physical fitness level was the same. For players filmed in more than 1 game, an average value for the games has been calculated and used in the analyses. All players were elite athletes with high training status, and the games were played during the season when the players are physically well prepared for games. The players followed their respective teams' preparations for nutrition and fluid. Thus, we did not interfere or alter the players' normal game preparations.

Each player was individually filmed during the entire games using a digital camera (Canon DM-MV 600, Canon Inc., Tokyo, Japan). The camera was positioned at the side of the pitch at the level of the midfield line, at a height of about 15 m, and at a distance of 30-40 m from the touchline. The videotapes were later replayed on a monitor for computerized coding of the activity pattern. The following locomotor categories were used: standing (0 km per hour), walking (6 km per hour), jogging (8 km per hour), low-speed running (12 km per hour), moderate-speed running (15 km per hour), high-speed running (18 km per hour), sprinting (25 km per hour), and backward running (10 km per hour). The locomotor categories were chosen in accordance with Krustrup et al. (9) and Mohr et al. (15). The above activities were later divided into 4 locomotor categories: (a) standing; (b) walking; (c) low-intensity running, encompassing jogging, low-speed running, and backward running; and (d) HIR, consisting of moderate-speed running, high-speed running, and sprinting. The frequency and duration of each activity were recorded in 5-minute periods throughout the game. The distance covered for each activity within each interval was determined as the product of the total time and mean speed for that activity. The total distance covered during a game was calculated as the sum of the distances covered during each type of activity. In the study by Krustrup and Bangsbo (7), it was observed that the coefficient of variation for test-retest analysis was 1, 2, 5, 3, and 3%, respectively, for total distance covered, walking, low-intensity running, HIR, and backward running. The intraindividual variations in walking, low-intensity, high-intensity, running, and backward running were 2, 5, 3, and 3%, respectively. All game recordings included in the present study were analyzed by 2 experienced observers. Each player was analyzed by the same observer in the domestic and international games. The data are presented for 5-, 15-, 45-, and 90-minute periods.

To compare the HR between the game types, 15 players worn a HR monitor (Team system; Polar Electro OY, Kempele, Finland) during the games. Data were collected continuously every 5 seconds during the games and analyzed using Polar Precision Performance 4.0 Program. The players' peak HR was established performing the Yo-Yo intermittent endurance test level 2 or the Yo-Yo intermittent recovery test level 2 (3,10) on an indoor surface.

Statistical Analysis

Descriptive statistics are represented as mean ± SD. The movement analysis data and HR data are represented as mean ± SE. Tests of normal distribution (Shapiro-Wilk's test) were conducted on all data before analysis, and data were normally distributed (p ≥ 0.05). Differences between the international and domestic games and differences between the first and second halves were tested by using a Student's paired t-test. Differences between the 5- and 15-minute periods within a game type and between game types were analyzed using a 2-way analysis of variance with repeated measures (game type × time). Where applicable, Tukey's Post Hoc test was used to identify specific differences within the data. Statistical power calculations were also performed in each analysis. p values below 0.05 were considered statistically significant.

Results

Number of Game Activities

The mean duration of the games was similar between the game types (93.1 ± 0.5 minutes INT vs. 92.2 ± 0.3 minutes DOM). The number of game activities was also similar between game types (1,641 ± 41 INT vs. 1,593 ± 30 DOM). The number of high-intensity runs was significantly (p < 0.05) higher in INT compared with DOM (187 ± 15 vs. 168 ± 12), whereas no difference was found for the number of sprints (23 ± 2 vs. 20 ± 2, NS). In INT, the players spend 20.9 ± 1.0% of the total game time standing, 42.8 ± 1.4% walking, 30.6 ± 1.5% running at low intensities, and 3.9 ± 0.5% backward running, which did not differ significantly from DOM. However, the players spend longer relative time sprinting (0.65 ± 0.06 vs. 0.54 ± 0.05%, p < 0.05) in INT compared with DOM. When comparing the 2 halves within INT, the players spent more relative time (p < 0.05) at both low and high intensities during the first compared with the second half (31.3 ± 1.5% vs. 29.9 ± 1.5% for low intensity, 6.3 ± 0.5% vs. 5.5 ± 0.5% for high intensity) but no differences were found in sprinting between the halves (0.7 ± 0.1% vs. 0.6 ± 0.1%). Similar differences were observed within DOM when comparing the 2 halves: low-intensity running (32.9 ± 1.6% vs. 30.5 ± 1.8%), HIR (6.4 ± 0.7% vs. 5.2 ± 0.5%) (p < 0.05), and sprinting (0.56 ± 0.07% vs. 0.51 ± 0.04%, NS). The statistical power of the tests above ranged from 55 to 87%.

Distances Covered

The total distance covered, the total running distance (total distance covered except walking), and the distance in backwards running did not differ between the game types (Table 1). The distance covered in HIR was ∼13% higher (p < 0.05) in INT compared with DOM (Table 1). Also, more HIR distance was observed in INT compared with DOM during both first and second half (Table 1). The total sprint distance was ∼14% higher (p < 0.05) in INT compared with DOM, and the difference was due to more sprinting in INT during the first half (Table 1). When comparing the 2 halves within INT, total distance covered during the first half was longer (p < 0.05) than the second half, whereas no difference was found between the halves within DOM (Table 1). The players covered longer distance (p < 0.05) in HIR during the first compared with the second half within both game types (Table 1), whereas no difference was found in sprinting distance (Table 1). The statistical power for total distance and HIR ranged from 68 to 96%, whereas the statistical power for sprinting distances was 37 to 38%.

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Table 1:
Total distance, total running distance, and high-intensity running and sprint distance during first and second half and total games during international and domestic games.*

Game Activity Changes Within the Games

When analyzing the games into shorter periods, we observed that more (p < 0.05) HIR was performed in the first four 15-minute periods (i.e., first 60 minutes) of INT compared with DOM (0.27 ± 0.02 km vs. 0.23 ± 0.02 km) (Figure 1). In INT, the HIR in the final 15-minute period of the game (0.20 ± 0.02 km) was lowered (p < 0.05) by 27% compared with the first 60-minute period (0.27 ± 0.02 km). In DOM, the HIR in the last 15-minute period of the game (0.18 ± 0.02 km) was lowered (p < 0.05) by 24% compared with the mean values for the first 45 minutes of the game (0.23 ± 0.02 km) (Figure 1). Nevertheless, the relative decline in HIR between the first and last 15-minute periods of the game was ∼24% both for INT and DOM (61 ± 23 and 56 ± 18 m, respectively; NS). When comparing the sprint distance between INT and DOM, more (p < 0.05) sprint distance was performed in 0-60 minutes of INT compared with DOM. When analyzing the sprint distance into 15-minute periods within INT, more sprint distances were observed in 15-30 minutes compared with all other 15-minute periods of the game. No differences were found within DOM for sprint distance (Figure 2). The statistical power of the tests above ranged from 63 to 99% for HIR and 39 to 40% for sprint.

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Figure 1:
High-intensity running (HIR) distance in 15-minute periods throughout the game for 17 elite female players. *Significantly (p < 0.05) lower compared with the periods 0-60 minutes of the international game. §Significantly (p < 0.05) lower compared with the periods 0-45 minutes of the domestic game.
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Figure 2:
Sprinting distance in 15-minute periods throughout the game for 17 elite female players. *Significantly (p < 0.05) higher compared with the domestic game.

The peak 5-minute HIR was 151 ± 7 m in INT and 134 ± 6 m in DOM (∼13%, NS, p = 0.06). In the following 5-minute period, the amount of HIR was 79 ± 11 and 67 ± 8 m, respectively (NS). Furthermore, the HIR in the peak distance in INT (151 ± 7 m) was 52% higher than the average distance covered during all 5-minute intervals not including the peak distance (73 ± 35 m). In DOM, the peak distance was 53% higher (134 ± 6 m) than the average distance covered during all 5-minute intervals not including the peak distance (63 ± 31 m) in DOM.

For sprint distance in 5-minute periods of the game, we observed that the sprint distance was 28% higher (p < 0.05) in the period 15-20 minutes of INT compared with DOM. Additionally, the peak 5-minute sprint distance was also significantly longer (p < 0.05) in INT compared with DOM (43 ± 3 m vs. 35 ± 3 m) (∼20%). In the following 5-minute period, the amount of sprinting was similar in both INT and DOM (13 ± 3 m). Furthermore, the sprint peak distance in INT was 4-fold higher than during all 5-minute intervals not including the peak distance (11 ± 2 m). In DOM, the peak distance was more than 3-fold higher than the average distance covered during all 5-minute intervals not including the peak distance (10 ± 2 m). The statistical power of the 5-minute period between game types ranged from 28 to 57%.

Playing Position

Due to low number of subjects, the forwards (n = 3) are not included in the statistical calculations between playing positions. Therefore, the comparison between and within playing position includes the midfielders (n = 5) and defenders (n = 9). When comparing player positions between the game types, the midfielders covered longer (p < 0.05) total distance (Table 2) and HIR (Figure 3) in INT compared with DOM. For the defenders, no significant difference was found between the 2 game types (Table 2 and Figure 3). When comparing sprint distance and players' position between the game types, the midfielders sprinted significantly longer in INT compared with DOM (Table 2). This corresponds to 43% more (p < 0.05) sprinting distance for midfielders in INT vs. DOM. When comparing playing positions within each game type, we observed that the midfielders covered more total distance (Table 2) and HIR (1.9 ± 0.2 km vs. 1.3 ± 0.1 km; Figure 3) than the defenders in INT. In DOM, no significant differences were found between positions. When comparing the 2 halves within each game type, the midfielders ran significantly more in total distance, but not HIR or sprinting, in the first half compared with the second half (5.4 ± 0.1 km vs. 5.2 ± 0.1 km) in INT. For the sprint distance within each game type for playing positions, no differences were observed (Table 2). The statistical power of the difference between positions for total distance and HIR was 72-87% and for sprint it was 28-36%.

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Table 2:
Total distance, total running distance, and sprint distance for different playing positions in total games during international and domestic games.*†
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Figure 3:
Distance in high-intensity running (HIR) for the different playing positions (defenders n = 9, midfielders n = 5, forwards n = 3). *Significantly (p < 0.05) higher compared with domestic games. #Significantly higher (p < 0.05) compared with defenders in the international game.

Number of Sprints and High-Intensity Runs During Games

The midfielders made on average 34% more sprints in INT vs. DOM (27 ± 4 vs. 20 ± 3, p < 0.05) and 24% more high-intensity runs (239 ± 30 vs. 193 ± 21, p < 0.05), whereas no differences were observed between game types for defenders, as they performed a similar number of sprints (21 ± 3 vs. 19 ± 3) and high-intensity runs (149 ± 15 vs. 151 ± 14) in INT vs. DOM. The statistical power for number of high-intensity runs and sprints was 50%.

Although not tested statistically, due to a low number of subjects, it may be of interest to report that the forwards performed on average 25 ± 5 maximal sprints and 208 ± 29 high-intensity runs in INT and 18 ± 3 sprints and 180 ± 31 high-intensity runs in DOM. This corresponds to a difference of 37% for number of sprints and 16% for number of high-intensity runs for the forwards between the game types.

Heart Rate During the Game

The peak HR was 187 ± 2 b·min−1 (97 ± 3% HRpeak) in INT and 185 ± 2 b·min−1 (97 ± 2% HRpeak) in DOM (NS). Furthermore, the average HR in the whole game, between halves (Table 3) or in 15-minute periods of the game, did not differ between game types. When comparing HR within INT, the HR was higher (p < 0.05) in period 15-30 minutes (167 ± 9 b·min−1) compared with the first 15 minutes of the game (162 ± 7 b·min−1), periods 45-60 minutes (158 ± 8 b·min−1), and 75-90 minutes (162 ± 9 b·min−1) of the game. Within DOM, the HR in the period 15-30 minutes was significantly higher (163 ± 10 b·min−1) than the period 45-60 minutes (158 ± 8 b·min−1) of the game. When analyzing the HR into 5-minute intervals, the first 5-minute periods of both halves in INT were significantly lower compared with the remaining 5-minute periods of the game. In DOM, the first 5-minute periods of both halves were lower to all the 5-minute periods in the first half but not in the second half. No significant differences were found in the 5-minute periods between the INT vs. DOM game. The statistical power for average HR and peak HR was 50% and for each 15- and 5-minute period was 26-51%.

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Table 3:
Mean heart rate in beats per minute and percentage of HRpeak during first and second half and total games during international and domestic games.*

Discussion

This study aimed to compare the exercise intensity and fatigue development for the same elite female players in 2 game types: international and domestic league soccer games. The main findings are that (a) the same players, mainly the midfielders, covered longer distances at high intensities and sprinted further in the international games compared with domestic league games, (b) the players' fatigue pattern during the games did not significantly differ between game types, and (c) mean and peak HR did not differ between game types. The difference in HIR distance observed between the game types was due to more frequent, not longer duration of, high-intensity activities in the international games. Furthermore, more sprinting occurred in the international compared with domestic games. This indicates more high-intensity work performed in the international games. This is similar to what has been shown in high-level female players in international compared with friendly games and small-sided training (6). It is also in agreement with studies showing that the work performed during a game is higher for players in higher competitions levels compared with players in lower competition levels (15,16). The novel finding of this study is that the same player, with the same fitness level, performed different amount of HIR in 2 different game types. More specifically, the difference in HIR between game types occurred in the first 60 minutes of the game, while the players performed similar amount of work at the end of both game types. Moreover, we observed that the higher work performed during international games was contributed mostly by the midfielders. The midfielders performed on average 7 more sprints and 46 more high-speed runs in the international compared with the domestic games. This shows that the midfield players were able to perform more runs in the international game and indicates that the midfielder's physical fitness allows them to work at a higher level than what they do in the domestic games. Unexpectedly, even though the players covered more HIR in the first 60 minutes of the international game, no significant difference was observed between the game types in the reduction of HIR in the last 15 minutes of the game. Reduction of HIR toward the end of games has been previously shown in studies on male (11,16,17) and female (9,12,15) players and indicates fatigue. However, as shown in Figure 1, the gradient of decline in HIR during the last 30 minutes of the games seems steeper in the international games compared with the domestic games. This may imply that the fatigue development was in fact larger toward the end of the international compared with the domestic league game. Our observations suggest that the players' fatigue resistance is likely challenged to a higher level in international compared with domestic games. Alternatively, it could be speculated that the reason for the reduction in HIR toward the end of the games may differ between the game types. As more HIR was performed by the midfielders in the international game, it is likely that the reduction in HIR in the international games was caused by physically fatigue, whereas in the domestic games, the reduction in HIR may have be related to the game outcome or the game tactics. The midfielders also covered more HIR compared with the defenders in the international games, indicating that they are able to physically work at a higher level than the defenders. The defenders, on the other hand, performed similar work in both game types, which indicates that they may have used their full physical capacity during both game types. Thus, a novel finding of this study is that the midfielders seem to be more physically taxed in international games and seem to perform more work in international than domestic games, whereas the defenders may be limited by their physical capacity. Indeed, several studies have previously found that defenders, in general, have lower fitness level compared with midfielders and forwards (8,9,11,14,15). It could be argued that the reason for the reduction in HIR toward the end of the games was due to tactics and game outcome for both game types. However, in our study, the decline in HIR occurred despite the fact that all international games were either European Championship qualifying games or Women's UEFA Cup games, where the losing team would be eliminated. In several international games, the scores were even until the end of the games. Hence, the game outcome most probably did not influence reduction in HIR toward the end of the international games.

Noteworthy, we observed large individual variations in the fatigue development during the games. Eleven of the 17 players performed less HIR in the last 30 minutes in the international compared with the domestic games, indicating that the majority of the players experienced a higher degree of fatigue in the international games. Thus, if more players had been included in the study or if using an even more precise measurement for analyzing distances covered, such as the multiple camera approach, differences in fatigue development may have been detected. As exemplified in Figure 4, 1 forward and 1 defender had a large decline in HIR in the second half, whereas the midfielders only had a small decline in HIR in the international games. Similar fatigue development was observed in sprint distances. One forward, for example, sprinted 110 m in the 45-60 minutes, whereas no sprint was observed in the last 15-minute period of the game. Another forward sprinted similar distance in the first (22 m) and last 15-minute period (18 m) of the second half. Similarly, one central midfielder sprinted 94 m from 45 to 60 minutes but only 37 m in the last 15-minute period of the game, whereas another midfielder sprinted similar distances (68 vs. 76 m). Altogether, this indicates that the fatigue development during games depend not only on the player's position but also on the individual player's style of playing, tactical role, and physical capacity. This suggests that training should be individualized depending on the player's needs but should consequently aim to make sure all players are able to perform HIR during the whole 90-minute games.

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Figure 4:
High-intensity running (HIR) distance in 15-minute periods throughout the international games for 4 individual players.

Despite differences in the workload between the 2 game types, we found no difference in HR measures. This indicates that mean HR response does not adequately reflect differences in high-intensity activities. Also, the average HR did not decrease despite a decline in HIR toward the end of the game. This could, however, be due to factors such as change in substrate utilization and dehydration that may occur toward the end of games (2,11). Nevertheless, the HR data should be interpreted with caution as we were unable to register the HR data during all games for all players.

Our findings that some players perform more HIR in the international compared with domestic games may have implications for the recovery time after a game. It has been shown that several performance parameters are long term reduced after a game where the players covered similar amount of HIR as in the domestic games of the present study (1). It was reported that sprint ability, jump, and isokinetic knee strength were reduced, and muscle damage indicators (creatine kinase and perceived muscle soreness) were elevated for several days (>69 hours) after a game in high-level female players (1). This suggests that after competitive international games, where more HIR distance is covered compared with domestic games, the performance and muscle damage parameters may be affected even longer time. Consequently, this may prolong the recovery time after international games and should be taken into consideration by coaches and trainers. This is especially important to consider during international women soccer tournaments that allow only 2 days of recovery between games.

In conclusion, the present study shows that the same elite female players performed more HIR and sprinting in the international compared with domestic games, whereas no differences were observed in total distance covered and HR response. This indicates that international games are more intense than domestic games. Furthermore, we found that fatigue occurred at the end of both game types. Although not significantly different, our data point toward a larger decline in HIR toward the end of the international games, which may be due to fatigue and/or inability to recovery from high intense running bouts.

Practical Applications

Our data suggest that the fitness training for elite women soccer players should aim at implementing individualized high-intensity aerobic training and speed endurance training to meet the physical challenge during international games. This type of training may also improve the ability to sustain high exercise intensity throughout a 90-minute game and hence affect the outcome of the games. In addition, the tactical aspect of an international game may also be considered to regulate the intensity and energy demands for certain players and positions to be able to perform at a high level throughout the whole game.

Acknowledgments

We thank the soccer players who participated in the study. The technical assistance of Tine Cederkvist Viskær, Mads Bendixen, Rasmus Bischoff, Christoffer Krustrup, and Sofie Rejkjær Svendsen is appreciated.

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Keywords:

match analysis; intermittent exercise; standard of play; fatigue

© 2010 National Strength and Conditioning Association