Authors: Joanne Spalding¹, Andrew R. Dotterweich², Jeremy Gentles², Brandi Eveland-Sayers², Adam L. Sayers²
¹Department of Health & Human Performance, Milledgeville, United States of America
²Department of Sport, Exercise, Recreation, and Kinesiology, East Tennessee State University, Johnson City, United States of America
Andrew R. Dotterweich
East Tennessee State University
Department of Sport, Exercise, Recreation and Kinesiology
P.O. Box 70671
Johnson City, TN 37614
Andy R. Dotterweich, PhD, is a Professor of Exercise Science at East Tennessee State University. His research interests include youth sport, recreation management and policy, physical activity, long-term athlete development and community development.
Joanne Spalding, PhD, is a lecturer in Exercise Science at Georgia College and State University. Her research interests include long term athletic development and monitoring at the club, high school, and college level.
Jeremy Gentles, PhD is an Associate Professor of Sport Science and Coach Education at East Tennessee State University in Johnson City, TN. His research interests include long term athlete monitoring, biochemical responses to exercise and sport technology.
Brandi Eveland-Sayers, PhD, is an Associate Professor of Exercise Science at East Tennessee State University. Her research interests include physical literacy, exercise adherence in youth, and long term athlete development.
Adam L. Sayers, PhD, is a faculty member in Global Sport Leadership at East Tennessee State University. He is also a network professional sport scientist for the United States Soccer Federation Youth Women’s National Teams, and a national instructor for USSF Coach Education.
Changes in Vertical Jump Height and Sprint Time During a Congested Match Schedule in Youth Female Soccer Players
Purpose: The purpose of this study was to examine changes in jump height and sprint time and to assess the relationship between relative changes in jump height and accumulated training load during a congested match schedule in youth female soccer players. Methods: This study included data from 14 youth female soccer players who performed countermovement jump testing pre- and post-match, post-tournament, as well as sprint testing pre- and post-tournament. A one-way repeated measures ANOVA was conducted to compare changes in jump height over the course of the tournament. A paired sample t-test was performed to compare sprint time between pre- and post-tournament, and Pearson product moment correlations were used to determine the relationship between percent change in jump height and accumulated training load. Results: Jump height decreased significantly (p < 0.001) between time periods during the tournament, and sprint time increased significantly (p = 0.001). There was no significant relationship between percent change in jump height and accumulated training load. Conclusion: This study found that jump height decreased over the course of the tournament and there was a significant increase in sprint time from pre- to post-tournament. Applications in Sport: These results suggest that appropriate recovery strategies and training are needed to assist players in coping with the demands of a congested youth soccer schedule.
Intermittent sports such as soccer require athletes to engage in bouts of high-intensity activity (e.g., sprinting, running, kicking, jumping, tackling) separated by lower-intensity activities (e.g., jogging and walking) (39-40). Research suggests that performance in high-intensity activities temporarily declines after competition (7,36,44) and the decline may persist up to 72 hours post-match (6,10,28,39-40). Therefore, if players are required to play in multiple games per week, resulting in a congested match schedule, fatigue may accumulate and cause performance to decline further. Youth soccer players in the United States (U.S.) are exposed to frequent congested match schedules throughout the season, playing from 2-4 matches per weekend. Therefore, assessing fatigue in players that participate in congested match fixtures could be beneficial to coaches and players trying to minimize deteriorations in performance.
In traditional 11 vs. 11 and youth level soccer games in the U.S., two 40-45 minute halves are played. The time per half differs depending on the level of play and type of competition. For example, high schools designate 40-minutes per half, state leagues for club level players require 45-minute halves, and tournaments with multiple games played in 2-3 days designate 35 to 40-minute per half. This game format is comparable to other youth levels that generally play 45-minute halves (24). In modern soccer, periods of fixture congestion (i.e., two or more games in a week) occur at all levels, especially for those teams competing in multiple events (e.g., leagues, tournaments, friendlies). A congested schedule may compromise fatigue management, cause underperformance, and increase the risk of injury (10,18). The degree of fixture congestion differs depending on the level of play. For instance, elite soccer players can play two or three matches in the same week due to participation in league and tournaments, as well as players who attend National Team Camps (23). Whereas, in youth soccer tournaments a congested match schedule often includes two to three matches played per day, or three to five matches played over the course of a weekend; in some instances, players are required to participate in five to six matches over a three-day period. Therefore, it may be assumed that these schedules affect match performance across consecutive games and more importantly during critical games (semi-final and final) played on the last day (3). This assumption is based on previous studies that showed fatigue accumulated over successive matches adversely affects physical performance when time between matches was short (2,8,10,13,24).
Match congestion may not only have a negative influence on player performance, but also player health. Ekstrand et al. (19) found that players above age 14 had similar types and rates of injuries as adult players. However, limited information is available detailing the influence of match-congestion on youth soccer players (11). In a review of literature by Faude et al. (21) the authors concluded that most studies have addressed frequency and total number of contact vs. non-contact injuries in soccer, but did not address the possible risk factors associated with contact and non-contact injuries. The rate of maturation and player biological and training age, may be factors that influence the frequency and type of injuries, particularly if youth players participate in excessive volumes of training and match play (29).
Assessment of the time-motion characteristics of soccer match play, including measures such as total distance and high-speed running, have been investigated during single-match weeks, and recently during congested match schedules. While a variety of methods have been used to assess the time-motion characteristics of soccer, much of the literature has used Global Navigation Satellite Systems (GNSS) such as Global Positioning Systems (GPS) units to quantify the demands of congested match schedules (24). Results indicate that total distance and distance covered at high-intensity (high speed running at >15.5km/h or sprinting at >20km/h) were not influenced by the short recovery periods between matches during a congested match schedule (18, 31, 32, 37, 40). Most youth clubs will not have the adequate budget and personnel to acquire and use expensive tools such as GPS, heart rate sensors and accelerometers. Therefore, simple and cost-effective methods to measure perceived exertion (RPE) of a player may be useful to youth soccer clubs. While there is a growing body of literature addressing congested match schedules for elite or professional level players, at the time of writing this paper, the researchers are not aware of a single study of congested match play in youth female soccer in the United States.
Session rating of perceived exertion (sRPE) is a subjective measure of game intensity as reported by players. sRPE is a simple, versatile, and cost-effective method to monitor training load in players during training sessions and matches (33) which has been used in a variety of team-based sports including rugby league (41), basketball (42), and Australian rules (43). Capranica & Millard-Stafford (9), indicated that sRPE is a more appropriate way of measuring internal training load for youth training compared to other methods. A study by Casamichana et al. (11) found an association between sRPE and total distance covered during training in semi-professional soccer players. It has also been found that high-speed running and numbers of impacts and accelerations may be predictors of sRPE during elite soccer training (36). Marynowicz et al. (34) found similar results while monitoring training over the course of a season in youth soccer players. The authors found a large relationship between sRPE and total distance which impacts player load and high-speed distance covered during training and matches. Since research indicates there is a relationship between sRPE, total distance covered, and player load, there is merit to evaluating the relationship between changes in countermovement jump (CMJ) height and sRPE to assist in determining the degree of fatigue induced during a congested match schedule.
Measures of physical performance have also been used as an indicator of fatigue in soccer. Tests of countermovement jump (CMJ) and sprint performance have been of particular interest, as they are sensitive to fatigue and each utilize the stretch-shortening cycle (7). It has been noted that participation in a congested match schedule may have implications for player performance. Decrements in physical performance can be monitored through CMJ testing as previous research has shown that fatigue negatively impacts CMJ performance (27). While most literature has evaluated jump performance in adult or elite athletes, a study by Oliver, Armstrong and Williams (38) focused on performance of youth male soccer players (age = 15.8±0.4). Assessing squat, countermovement, and drop jump performance before and after a 42 min soccer-specific exercise test, the authors found that jump height decreased from pre- to post-exercise test for all jump types., (38). In a study by Hoffman et al., (25) 19 NCAA Division III female soccer players were jump tested 24 hours before, immediately after, and 24 hours post-match to determine the effect of a competitive match on peak power and peak force during jumping. The authors found that both peak power and peak force were maintained throughout the duration of a soccer match, but declined significantly within 24 hours post-match (25). Although, CMJ is a useful method to monitor fatigue in soccer players, not all soccer clubs will have access to force plates, software, mats, or the personnel to monitor the data. Therefore, the use of an alternative method could be useful for practitioners, and the use of sprint testing has been used to quantify fatigue (30).
Sprint performance is important during critical moments of match play (e.g., counterattacks, intercepting, tackling, and shooting) and athletes may spend up to 11% of game time sprinting (5,15). Andersson et al. (2) found that 20m sprint performance significantly decreased immediately following single match play but returned to baseline within five hours in elite female soccer players. Similarly, a study by Rey et al., (40) found that the number of sprints and high-speed runs did not change after a single 90-minute match. Changes in jump and sprint performance resulting from fatigue caused by congested match schedules have not been thoroughly investigated at the female youth level, warranting further investigation.
Although sRPE, CMJ and sprints have been useful methods to indicate fatigue post-match, data are limited during congested match schedules. Additionally, there is a lack of literature investigating how these variables are affected during a congested match schedule in female youth soccer players. Therefore, the purposes of this study were to analyze changes in jump height and sprint time, and the relationship of jump height and match load (min played and sRPE, during a competitive youth soccer tournament in female players.
Experimental Approach to the Problem
This study focused on assessing changes in CMJ height (measured by the vertical jump) and sprint time during a congested match schedule as well as the relationship between relative changes in CMJ height and match load (min played and sRPE). Vertical jump testing, RPE collection, minutes played, and sprint testing took place throughout a youth soccer tournament.
A total of 20 division I state league female youth (under 16) soccer players from the same team (age = 14.7 ± 0.2 years, weight = 58.1 ± 1.9 kg, height = 116 ± 1.2 cm) participated in the study. The participants were athletes from a team which was already engaged in an athlete monitoring program. Athletes took part in the team’s normal athlete monitoring program during the spring tournament season. All athletes were not available for some sessions or games due to scheduling conflicts and were not included in the study. Due to substitution rules, subjects who participated in 70% of minutes played were included in the study. As a result, 14 athletes satisfied the criteria and were included for analysis. This study was approved by East Tennessee State University’s Institutional Review Board (IRB) and informed consent was obtained.
Located approximately 4.5 travel hours from player homes in Johnson City, Tennessee (USA), the tournament comprised three matches across two days. Travel occurred the day before the first match. The first match consisted of 40-minute halves with a 10-minute half-time. The subsequent two matches were contested over two 35-minute halves with a 10-minute half-time. Matches changed in duration due to tournament scheduling, and to prevent conflict with incoming inclement weather. Matches one and two were played on the same day, separated by approximately four hours. Match three was played on the second day, approximately 13 hours after match two. Unlimited substitutions were allowed for all matches.
Vertical Jump Assessment
Vertical jump assessment was performed pre-tournament, after each match (three matches), and post-tournament. The pre-tournament assessment occurred during the last training session before the tournament and prior to any physical activity. Post-match assessment was performed within 30 min of the match ending. The post-tournament assessment occurred at the next training session, 24 hours after the tournament ended and prior to any physical activity.
Vertical jump kinetic data was collected via a single 2-axis force platform (PS-2142; PASCO, Roseville, CA), measuring at 1,000 Hz. The plate was positioned in a custom frame to prevent slippage. The top of the force plate was flush with the frame. Jumps were analyzed using a custom spreadsheet (14), specifically designed to analyze CMJ and variables associated with CMJ. Subjects completed a standardized dynamic warm-up protocol prior to vertical jump testing during the pre- and post-tournament sessions. It was unnecessary for subjects to perform the warm-up again post-match. For each CMJ, subjects completed two trials with 20 seconds rest between each trial. CMJ depth was self-selected with no pause occurring between eccentric and concentric phases. Subjects stood upright on the force platform and were given the command “3, 2, 1, jump”. If the investigator deemed a trial to be a bad jump (e.g., submaximal effort, lifting legs prior to landing, or jumping to one side), a third trial was completed. The average of the two trials was retained for statistical analysis. Intrasession CMJ heights were deemed reliable with a coefficient of variation of 5.14%.
20-meter sprint assessment
Subjects performed the 20-meter sprint test immediately following the vertical jump assessment. Subjects performed two trials each, with 90 seconds of rest between each trial. The time taken to run 20 m was measured using optical timing gates (Brower, IR Emit, Draper, Utah, USA). The subjects started from a standing position three inches before the timing gate. This starting position ensured that the torso first broke the line. When ready, the subject sprinted through to the next timing gate at maximum effort. The best of two trials was reported for comparison between pre and post-tournament (46).
Match Load Calculation
Rating of perceived exertion (RPE) was assessed approximately 10 minutes following each match, modified Borg CR 10-scale as described in Foster et al. (22). Session rating of perceived exertion was calculated by multiplying the players RPE by total min played (1). Total accumulated match load was calculated as the tournament continued.
A one-way repeated measures ANOVA was performed to compare changes in jump height between pre-tournament (PRE), match one (M1), match two (M2), match three (M3), and post-tournament (POST). Mauchly’s test demonstrated the assumption of sphericity was not violated (p = 0.342). Post-hoc tests were completed using Bonferroni correction. A paired samples t-tests was conducted to compare sprint time pre- to post-tournament and a Shapiro-Wilk test verified the assumption of normality was not violated (p = 0.330). Ninety five percent confidence intervals and Cohen’s d effect sizes (d) were also calculated. Pearson product-moment correlations were calculated to assess the relationship between the change in jump height from PRE to M1, M2, M3, with total match load (min players and sRPE). The strength of a relationship as measured by Pearson product-moment correlation coefficients were evaluated with the following scale: r = 0.0-0.1 (trivial); r = 0.1-0.3 (small); r = 0.3-0.5 (moderate); r = 0.5-0.7 (large); r = 0.7-0.9 (very large); r = 0.9-1.0 (nearly perfect) (26). The critical alpha level was set at p ≤ 0.05. Statistical analyses were conducted using JASP software (JASP Team, JASP (Version 0.9), 2018).
A statistically significant difference in jump height was found for time (F(4,13) = 9.061, p < 0.001) (Figure 1). Post hoc testing revealed multiple significant differences in jump height as shown in Table 1. There was also a statistically significant increase (t(13) = -12.12, p = 0.001, d = -3.24) in sprint time at post-sprint time (3.751 ± 0.17s) compared to pre-sprint time (3.351 ± 0.12s) as illustrated in Figure 2.
Table 1. Differences in jump height between time periods.
|Time||CI||Cohen’s D||P bonf|
Figure 1. Change in Jump Height 95% Confidence interval
Figure 2. Change in sprint time pre- to post-tournament with 95% Confidence interval
Table 2 details minutes played, RPE and sRPE for each participant and match, as well as group mean and SD. There were no statistically significantly correlations found between relative changes in CMJ, and match load (min played and sRPE).
Table 2. Match Load (Minutes played and RPE)
|Athlete||Match 1||Match 2||Match 3|
|Minutes played||RPE||sRPE||Minutes played||RPE||sRPE||Minutes played||RPE||sRPE|
|Mean ± SD||91.78 ± 26.96||751.0 ± 259.5||75.8 ± 9.9||563.9 ± 111.9||81.0 ± 14.7||619.04 ± 150.0|
The purpose of this study was to assess changes in performance variables during a congested match schedule, and the relationship between relative changes in jump height and match load during a youth female soccer tournament to highlight fatigue accumulation. This study found multiple statistically significant changes in jump height (decrease), and sprint times increased significantly from pre- to post-tournament. No statistically significant correlations were found between match load and relative changes in jump height.
Statically significant differences were found between pre-tournament jump height and post-match jump height at different times (p=0.001), and at no point were equal to pre-tournament jump height. The findings support pervious investigations (44-45) that found performance decreased from pre to post-match during a congested match schedule. It should be noted however, that players from prior studies were male and played at a semi-professional level. Results from this study show that there was a significant change (p=0.014) in jump height after the first match (0.239 ± 0.041) and from pre-tournament jump height (0.222 ± 0.044). Results from a Krustrup et al. (30), however, disagreed with results of the current study, as they found no difference in jump height after one match. However, the findings were not significant with pre (35 ± 1) and post (36 ± 1) match jump height differing by one centimeter. Of notable interest is that Krustup’s et al. study included elite level adult female players and only included one match. Hoffman et al., (25) also showed no change in jump height after only one match, but did show a decrease in jump performance after a 24-hour rest period. The current study showed that jump height decreased after a single match, and players never reached pre-tournament levels again. This finding indicates that congested match schedules may not provide sufficient recovery time between matches and could increase injury risk during match play (5,16).
The statistically significant (p = 0.041) decrease in jump height from pre-tournament (0.239 ± 0.041) to game one (0.222 ± 0.044) may indicate that players’ performance declines after one match. Results from this study are similar to those reported by Andersson et al. (2) who observed that jump performance was significantly impacted (p = 0.05) after one match with jumps decreasing by 4 ± 0.8% (2). Additionally, the results of this study concurred with Oliver et al., (38) who observed significant decrements (p < 0.05) of 3cm in jump height performance after 42 minutes of soccer-specific exercise. The significant change in jump height from pre to match three (p = <0.001), match two to match three (p = 0.010), and match three to post (p = 0.10) may indicate that accumulated fatigue and therefore injury risk, were greatest after the third match.
There was a significant increase in sprint time from pre- to post-tournament. This increase suggests that player performance may be affected at least 24 hours post-tournament and could have implications on training load before and after a congested match schedule, especially for those clubs that have training days within a 24-hour period. This study differs from Brownstein et al. (7) where straight-line 10-20m sprint performance was not indicative of fatigue 24-48 hours post-match (7). Other investigations have shown that sprint performance may recover within 5-96 hours (28, 35), but potentially decrease again following a subsequent match (2, 4, 17, 20). While there is variability in recovery time with sprint time in the studies mentioned, 20-meter sprint may still be a practical tool to monitor fatigue in soccer players after a youth soccer tournament.
There are several limitations of the current study. First, the data was collected from one team limiting the generalizability of this study. Secondly, the study included a small sample size affecting validity. Another shortcoming is that data was also collected from players of a single age group. Finally, data was collected over the course of a single tournament which limits the type of congestion investigated. Future research should focus on a longer observational period in which players participate in multiple competitions of varying congestion. It would also be beneficial for researchers to observe multiple age groups and determine if induced fatigue differs depending on maturation.
In summary, jump height was different across time periods over the course of the tournament with jump height never reaching pre-tournament scores. Changes in jump height from pre-tournament to match three decreased significantly, and match three jump height was lower compared to match one and match two vs pre-tournament scores, indicating that match three may be a significant time point in this type of congested schedule. There was a significant change in sprint time from pre- to post-tournament with sprint time increasing, indicating that it may be used to monitor fatigue in youth soccer players.
Applications in Sport
CMJ height and 20 meter sprint may be appropriate monitoring tools for sport practitioners to indicate fatigue during a competitive youth soccer tournament. Changes in a player’s vertical jump height may be a more practical means to assess match related fatigue during a congested match schedule compared to 20-meter sprint testing. Also, if players are required to participate in three matches or more, it may be beneficial for coaches and players to employ recovery and substitution strategies (e.g., data on minutes played for each player) to improve fatigue management. Jumps may also help practitioners prevent injuries during congested match schedules as results showed there is a significant change in CMJ performance which may be an indicator of neuromuscular fatigue.
- Acros, A., Yanci, J., Mendiguchia, J., & Gorostiaga, E. (2014). Rating of muscular and respiratory perceived exertion in professional soccer players. Journal of Strength and Conditioning Research, 28, 3280–3288.
- Andersson, H., Raastad, T., Nilsson, J., Paulsen, G., Garthe, I., & Kadi, F. (2008). Neuromuscular fatigue and recovery in elite female soccer: Effects of active recovery. Journal of Medcine & Science in Sports, 40, 372-380,.
- Arruda, A. F. S., Carling, C., Zanetti, V., Aoki, M. S., Coutts, A. J., & Moreira, A. (2015). Effects of a Very Congested Match Schedule on Body-Load Impacts, Accelerations, and Running Measures in Youth Soccer Players. International Journal of Sports Physiology and Performance, 10(2), 248–252. https://doi.org/10.1123/ijspp.2014-0148
- Ascensao, A., Rebelo, A., Oliveira, E., Marques, F., Pereira, L., & Magalhaes, J. (2008). Biochemical impact of a soccer match –analysis of oxidative stress and muscle damage markers throughout recovery. Clin. Biochem, 41, 841–851.
- Bengtsson, H., Ekstrand, J., & Haagglund, M. (2013). Muscle injury rates in professional football increase with fixture congestion: An 11-year follow-up of the UEFA Champions League injury study. Journal of Sports Medicine, 47(743–747).
- Bradley, P., Sheldon, W., Wooster, B., Olsen, P., Boanas, P., & Krustrup, P. (2009). High-intensity running in English FA Premier League soccer matches. Journal of Sports Sciences, 27, 159–168.
- Brownstein, C., Dent, J., Parker, P., Hicks, K., Howatson, G., & Goodall, S. (2017). Etiology and recovery of neuromuscular fatigue following competitive soccer match-play. Frontiers in Physiology, 25, 831.
- Buchheit, M., Horobeanu, C., Mendez-Villanueva, A., Simpson, B. M., & Bourdon, P. C. (2011). Effects of age and spa treatment on match running performance over two consecutive games in highly trained young soccer players. Journal of Sports Sciences, 29(6), 591–598. https://doi.org/10.1080/02640414.2010.546424
- Capranica, L., & Millard-Stafford, M. (2011). Youth sport specialization: How to manage competition and training? International Journal of Sports Physiology and Performance, 6, 572–579.
- Carling, C., Bloomfield, J., Nelsen, L., & Reilly, T. (2015). The Role of Motion Analysis in Elite Soccer: Contemporary Performance Measurement Techniques and Work Rate Data. . British Journal of Sports Medicine, 38, 839–862.
- Carling, C., Gall, L., & Dupont, G. (2012). Analysis of repeated high-intensity running performance in professional soccer. Journal of Sports Sciences, 30, 325–336.
- Casamichana, D., Castellano, J., Calleja-Gonzalez, J., San Román, J., & Castagna, C. (2013). Relationship Between Indicators of Training Load in Soccer Players. Journal of Strength and Conditioning Research, 27(2), 369–374. https://doi.org/10.1519/JSC.0b013e3182548af1
- Castagna, C., Impellizzeri, F., Cecchini, E., Rampinini, E., & Alverez, J. (2009). Effects of intermittent-endurance fitness on match performance in young male soccer players. Journal of Strength and Conditioning Research, 23, 1954–1959.
- Chavda, S., Bromely, T., Jarvis, P., Williams, S., Bishop, C., Turner, A., & Mundy, P. (2018). Force time characteristics of the countermovement jump: Analyzing the curve in excel. Strength and Conditioning Journal.
- Comfort, P., Stewart, A., Bloom, L., & Clarkson, B. (2014). Relationships between strength, sprint, and jump performance in well-trained youth soccer players. Journal of Strength and Conditioning Research, 28, 173–177.
- Dellal, A., Lago-Peñas, C., Rey, E., Chamari, K., & Orhant, E. (2015). The effects of a congested fixture period on physical performance, technical activity and injury rate during matches in a professional soccer team. British Journal of Sports Medicine, 49(6), 390–394. https://doi.org/10.1136/bjsports-2012-091290
- Djaoui, L., Diaz-Cidoncha Garcia, J., Hautier, C., & Dellal, A. (2016). Kinetic Post-match Fatigue in Professional and Youth Soccer Players During the Competitive Period. Asian Journal of Sports Medicine, 7(1). https://doi.org/10.5812/asjsm.28267
- Dupont, G., Nedelec, M., McCall, A., McCormack, D., Berthoin, S., & Wisløff, U. (2010). Effect of 2 Soccer Matches in a Week on Physical Performance and Injury Rate. The American Journal of Sports Medicine, 38(9), 1752–1758. https://doi.org/10.1177/0363546510361236
- Ekstand, J., Walden, M., & Hagglund, M. (2004). Risk for injury when playing in a national football team. Scandinavian Journal of Medicine & Science in Sports, 14, 34–36.
- Fatouros, I., & Jamurtas, A. Z. (2016). Insights into the molecular etiology of exercise-induced inflammation: Opportunities for optimizing performance. Journal of Strength and Conditioning Research, 9, 175.
- Faude, O., Rößler, R., & Junge, A. (2013). Football Injuries in Children and Adolescent Players: Are There Clues for Prevention? Sports Medicine, 43(9), 819–837. https://doi.org/10.1007/s40279-013-0061-x
- Foster, C. (1998). Monitoring training in athletes with reference to overtraining syndrome. Medicine and Science in Sports and Exercise, 30, 1164–1168.
- Fowler, P., Duffield, R., Howle, K., Waterson, A., & Vaile, J. (2015). Effects of northbound long-haul international air travel on sleep quantity and subjective jet lag and wellness in professional Australian soccer players. International Journal of Sports Physiology and Performance, 10, 648–654.
- Harley, J. A., Barnes, C. A., Portas, M., Lovell, R., Barrett, S., Paul, D., & Weston, M. (2010). Motion analysis of match-play in elite U12 to U16 age-group soccer players. Journal of Sports Sciences, 28(13), 1391–1397. https://doi.org/10.1080/02640414.2010.510142
- Hoffman, J. R., Nusse, V., & Kang, J. (2003). The Effect of an Intercollegiate Soccer Game on Maximal Power Performance. Canadian Journal of Applied Physiology, 28(6), 807–817. https://doi.org/10.1139/h03-060
- Hopkins, W., Marshall, S., Batterham, A., & Hanin, Y. (n.d.). Progressive Statistics for Studies in Sports Medicine and Exercise Science. Journal of Medcine & Science in Sport and Exercise, 41(1), 3–13.
- Horita, T., Komi, P., Hämäläinen, I., & Avela, A. (2003). Exhausting stretch-shortening cycle (SSC) exercise causes greater impairment in SSC performance than in pure concentric performance. European Journal of Applied Physiology, 88, 527–534.
- Ispirlidis, I., Fatouros, I., Jamurtas, A., Nikolaidis, M., Michailidis, I., Dourourdos, I., Margonis, K., Chatzinikolaou, A., Kalistrtos, E., Katrabasas, I., Alexiou, V., & Taxildaris, K. (2008). Time-course of changes in inflammatory and performance responses following a soccer game. Clinical Journal of Sports Medicine, 18, 423–431.
- Johnson, A., Doherty, P. J., & Freemont, A. (2009). Investigation of growth, development, and factors associated with injury in elite schoolboy footballers: Prospective study. BMJ, 338(feb26 1), b490–b490. https://doi.org/10.1136/bmj.b490
- Krustrup, P., Zebis, M., Jensen, J., & Mohr, M. (2010). Game-induced fatigue patterns in elite female soccer. Journal of Strength and Conditioning Research, 24, 437–441.
- Lago, C. (2009). The influence of match location, quality of opposition, and match status on possession strategies in professional association football. Journal of Sports Sciences, 27, 1463–1469.
- Lago-Peñas, C., Rey, E., Ballesterso, J., & Casais, L. (2011). The Influence of a Congested Calendar on Physical Performance in Elite Soccer. Journal of Strength and Conditioning Research, 10, 1–7.
- Lupo, C., Capranica, L., & Cortis, C. (2017). Session-RPE for quantifying load of different youth taekwondo training sessions. Journal of Sports Medicine & Physical Fitness, 57, 189–194.
- Marynowicz, J., Kikut, K., Lango, M., Horna, D., & Andrzejewski, M. (2020). Relationship Between the Session-RPE and External Measures of Training Load in Youth Soccer Training. Journal of Strength and Conditioning Research, 34(10), 2800–2804.
- Meeusen, R., Duclos, M., Foster, C., Fry, A., Gleeson, M., Nieman, D., & Gerard Rietjens, J. (2012). Prevention, diagnosis and treatment of the overtraining syndrome: Joint consensus statement of the European College of Sport Science (ECSS) and the American College of Sports Medicine (ACSM). European Journal of Sport Science, 1–24.
- Mohr, M., Krustrup, P., & Bangsbo, J. (2005). Fatigue in soccer: A brief review. Journal of Sports Sciences, 23, 593–599.
- Odetoyinbo, K., Wooster, B., & Lane, A. (2008). The effect of a succession of matches on the activity profiles of professional soccer players. Journal of Medcine & Science in Sports, 6, 105–110.
- Oliver, J., Armstrong, N., & Williams, C. (2008). Changes in jump performance and muscle activity following soccer-specific exercise. Journal of Sports Sciences, 26, 141–148
- Reilly, T., & Rigby, M. (2002). Effects of an active warm-down following competitive soccer. Science and Football IV, 226–229.
- Rey, E., Lago-Peñas, C., Lago-Ballesteros, J., Casais, L., & Dellal, A. (2010). The effect of a congested fixture period on the activity of elite soccer players. Journal of Biology and Sport, 181–185.
- Roe, G., Darrall-Jones, J., Till, K., Phibbs, P., Read, D., Weakley, J., Rock, A., & Jones, B. (2017). The effect of physical contact on changes in fatigue markers following rugby union field-based training. European Journal of Sport Science, 17(6), 647–655. https://doi.org/10.1080/17461391.2017.1287960
- Scanlan, A. T., Wen, N., Tucker, P. S., & Dalbo, V. J. (2014). The Relationships Between Internal and External Training Load Models During Basketball Training: Journal of Strength and Conditioning Research, 28(9), 2397–2405. https://doi.org/10.1519/JSC.0000000000000458
- Scott, T. J., Black, C. R., Quinn, J., & Coutts, A. J. (n.d.). Validity and Reliability of the Session-RPE Method for Quantifying training in Australian Football: A Comparison of the CR10 and CR100 Scales. 7.
- Thomas, K., Dent, J., Howatson, G., & Goodall, S. (2017). Etiology and recovery of neuromuscular fatigue after simulated soccer match play. Journal of Medcine & Science in Sports, 49, 955–964.
- Watkins, C., Barillas, S., Wong, M., Archer, D., Dobbs, I., Lockie, R., Coburn, J., Tran, T., & Brown, L. (2017). Determination of vertical jump as a measure of neuromuscular readiness and fatigue. Journal of Strength and Conditioning Research, 31, 3305–3310.
- Wisloff, C., Castagna, C., Helgerud, J., Jones, R., & Hoff, J. (2004). Strong correlation of maximal squat strength with sprint performance and vertical jump height in elite soccer players. British Journal of Sports Medicine, 38, 285–288.