The influence of soccer playing actions on the recovery kinetics after a soccer match

Football (soccer) match-derived hamstring muscles residual fatigue can be monitored using early rate of torque development

PURPOSE

The aim of this study was to determine whether a soccer match affects the rapid force-generating capacity of the hamstring muscles, given their key role in both horizontal ground reaction force production during sprint biomechanics, and in the deceleration of the shank during the late swing phase, where rapid force production is essential owing to time constraints. Therefore, the research objective was to determine soccer match-induced hamstrings residual fatigue and recovery through rate of torque development (RTD) and associated biochemical parameters.

METHODS

The recovery kinetics of hamstrings RTD metrics by the 90°hip:20°knee test, together with serum biomarkers (creatine kinase, mitochondrial creatine kinase, transaminases, malondialdehyde, irisin), were assessed in 19 male, regional first-division soccer players (age = 20.9 ± 2.0 years, mass = 72.6 ± 11.9 kg, height = 175.9 ± 6.9 cm [mean ± SD]), before a soccer match (MD) and post-24 h (MD+1), post-48 h (MD+2) and post-72 h (MD+3), through a repeated measures design.

RESULTS

Early RTD to 50 ms (p < 0.001, g = -1.24) and 100 ms (p < 0.001, g = -1.06) remained unrecovered on MD+3 in both hamstring muscles. However, maximal voluntary isometric contraction (MVIC) torque of the dominant and non-dominant hamstrings was unrecovered on MD+2 (p = 0.004, g = -0.91; and p = 0.002, g = -0.98, respectively) and recovered on MD+3 (p = 0.057 and p = 0.070, respectively). Further, neuromuscular deficits were coupled with myocyte structural (p = 0.002, g = 1.11) and mitochondrial damage (p = 0.004, g = 0.92) biomarkers.

CONCLUSION

Based in the findings, early RTD0-50 and RTD0-100 monitoring, through the 90°hip:20°knee IPC test, is a cost-effective method for assessing soccer match-induced hamstring muscles residual fatigue and recovery. Overall, soccer match-induced hamstring residual fatigue is not recovered within a 3-day recovery period. Practitioners can use rapid force production metrics through isometric assessments, providing a simple, non-exhaustive tool, for assessing residual fatigue status during congested competitive periods, to comprehensively balance muscle recovery with optimizing training.

Validation of the metabolic power model during three intermittent running-based exercises with emphasis on aerobic and anaerobic energy supply

Introduction

In intermittent sports, available internal load measurements like capillary blood techniques and portable respiratory gas analyzers are considered as gold standards in controlled laboratory environments, but are impractical for daily use in training and matches. A newer approach, the metabolic power model, allows to extrapolate from speed and acceleration data to the metabolic power, simulated oxygen uptake, and aerobic and anaerobic energy supply. The aim of this study was to validate the metabolic power model against the established 3-component model to allow direct comparison of variables including energy expenditure and supplies during intermittent running-based exercises.

Methods

Twelve male athletes (24 ± 3 years) performed three different running-based exercises consisting of continuous shuttle runs and repeated accelerations and sprints with change of direction. Each exercise condition intended to primarily stress the aerobic, anaerobic alactic, and lactic energy supply. One-way repeated measures ANOVA or Friedman test and corresponding effect sizes were applied for statistical analyses. Additionally, absolute and relative biases and Bland-Altman plots were generated.

Results

For total energy expenditure, there were statistically significant differences (p ≤ .002, d ≥ .882, large) and biases of -13.5 ± 11.8% for the continuous shuttle runs and up to 352.2 ± 115.9% for repeated accelerations and sprints. Concerning aerobic energy supply, there were statistically significant differences (p < .001, d ≥ 1.937, large effect sizes) and biases of up to -38.1 ± 11.7%. For anaerobic energy supply, there were statistically significant differences (p < .001, d ≥ 5.465, large) and biases of up to 1,849.9 ± 831.8%.

Discussion

In conclusion, the metabolic power model significantly under- or overestimates total energy expenditure and supplies with large effect sizes during intermittent running-based exercises. Future studies should optimize the model before it can be used on a daily basis for scientific and practical purposes.

Recovery Patterns of Low-frequency Fatigue in Elite Youth Soccer Players after Official Matches

This study aimed to analyze the associations between recovery of low-frequency fatigue, jump height, and perceptual responses following official soccer matches. Forty-two male youth elite soccer players (age: 17.13±0.70 years; height: 179.17±5.94 cm; weight: 69.74±4.91 kg) participated in this study. Low-frequency fatigue, countermovement jump, perceived fatigue, muscle soreness, and perceived recovery were assessed at - 2 h, +30 min, +24 h and +48 h relative to the match. Linear mixed models analysis showed that low-frequency fatigue was reduced at the match-end (ES=- 0.679 [95% CI =- 1.01; - 0.34]; p<0.001) but returned to baseline after 24 h (ES=0.149 [95% CI = - 0.26; 0.56]; p=1.00). Perceptual responses were impaired for up to 48 hours following the match (ES=- 0.868-1.174; p<0.001). Countermovement jump did not differ between any time point (ES=- 0.204-0.216; p>0.05). Additionally, the within-subject correlation analysis showed that low-frequency fatigue pre- to post-match changes presented moderate to large associations with perceived fatigue (rm[57]=- 0.43; p<0.001), muscle soreness (rm[57]=- 0.52; p<0.001), and perceived recovery (rm[57]=0.38; p=0.003). The assessment of low-frequency fatigue could serve as an additional objective measurement for monitoring post-match fatigue, as findings suggest that young elite soccer players experience transient reductions following match-play, which are strongly correlated with subjective markers of recovery.

Subjective recovery in professional soccer players: A machine learning and mediation approach

Coaches often ask players to judge their recovery status (subjective recovery). We aimed to explore potential determinants of subjective recovery in 101 male professional soccer players of 4 Italian Serie C teams and to further investigate whether the relationship between training load and subjective recovery is mediated by fatigue, sleep quality, muscle soreness, stress and mood. A complete season for each of the four teams was recorded for a total of 16,989 training sessions and matches. Every morning, players rated their perceived fatigue, sleep quality, muscle soreness, stress and mood, and judged their recovery using the Total Quality Recovery (TQR) questionnaire. Training load was obtained after each training session or match. A framework of data analytics of time series was employed to detect the factors associated with subjective recovery. Machine learning and mediation analyses suggest that TQR is primarily associated with ratings of fatigue and muscle soreness at the judgements time, and that these factors mediate most of the relationship between training load of the previous day and subjective recovery. These findings suggest that, to maximize subjective recovery, strategies minimizing fatigue and muscle soreness should be implemented. Reducing the training load of the previous day seems the most effective strategy.

The Influence of Game Intervals on Physical Performance Demands in Elite Futsal: Insights from Congested Periods

The aims of this study were to analyze (1) the external match demands during a congested period (CP) (i.e., three games in eight days) and (2) the differences among games with two- or three-day intervals in professional futsal players. Eleven elite male futsal players were monitored during 15 official matches. Wearable accelerometers were used to record player load (PL), accelerations (ACC), decelerations (DEC), and changes of direction (COD) at different intensities (e.g., high, medium, and low) using two approaches (e.g., absolute and relative per minute). A linear mixed model and effect sizes (ESs) were used to analyze differences between matches and days of interval. Considering the external match load during CP, non-significant differences were found for all the variables (p = 0.108-0.995; ES: 0.01-0.40). Comparing the interval days between games, players had significantly higher DECHI (p = 0.030; ES: 0.48), CODTOTAL (p = 0.028; ES: 0.33), CODMED (p = 0.024; ES: 0.40), and CODLOW (p = 0.038; ES: 0.31) following 3 days of interval between the games when compared with 2 days. However, when analyzed relative to effective time, non-significant differences were found. In summary, CPs seem to not affect the match external load, but players performed better in terms of DEC and COD following 3 days of interval when compared to 2 days when analyzed with absolute values.

Acute Effects of Foam Rolling and Stretching on Physical Performance and Self-Perceived Fatigue in Young Football Players

Background/Objectives: The aim of this study was to examine the acute effects of foam rolling and traditional stretch treatments on physical performance and self-perceived fatigue in youth football players. Methods: The sample of participants consisted of 20 youth football players from the Serbia Under-17 league. Participants were randomly assigned to one of two groups, the Foam group (age: 16.6 ± 1.5 years) or the Stretch group (age: 16.9 ± 1.0 years), with each group consisting of 10 participants. The first measurement (I) was conducted before the match; then, the football players played the match, which was followed by the second measurement (II), and afterward, the groups performed their foam and stretch activities. The third measurement (III) was conducted 2 h after the recovery interventions, and the fourth measurement (IV) was conducted 24 h after the match. Players were tested for the following: linear sprints at 5 m, 10 m, and 20 m, squat jumps (SJs), countermovement jumps (CMJs), and arm-driven countermovement jumps (ACMJs). Participants also completed self-assessment questionnaires on fatigue (Hooper scales) and perceived exertion (Borg scales). Results: A 2 × 4 split-plot ANOVA revealed that there were no differences between the foam rolling and stretching treatments in any parameter of physical performance or self-perceived fatigue. However, a separate within-group analysis showed that the Foam group achieved significantly better sprint times in the third and fourth measurements (2 and 24 h post-match, respectively) compared to measurements taken immediately after the football match. Regarding self-perceived parameters, foam rolling reduced fatigue and stress at 2 and 24 h post-match. On the other hand, the stretching treatment only affected the stress parameter, which was reduced 24 h after the football match. Conclusions: These findings indicate that although there were no significant differences between treatments, foam rolling demonstrated certain advantages compared to stretching. Specifically, foam rolling may offer benefits in enhancing subjective recovery and reducing perceived exertion in young football players. However, these conclusions should be interpreted with caution, as the study was cross-sectional and involved a small sample of young football players.

Potential Importance of Maximal Upper Body Strength-Generating Qualities and Upper Body Strength Training for Performance of High-Intensity Running and Jumping Actions: A Scoping Review

PURPOSE

To investigate the influence of upper body (UB) strength qualities and UB strength training on the performance of high-intensity running and jumping actions and to identify gaps and recommendations for future research.

METHODS

A systematic search using the PRISMA Scoping Review protocol was conducted in February 2024 using PubMed, Scopus, and ICTRP. Studies eligible for inclusion were those that reported associations between UB or trunk maximal strength qualities (e.g., absolute strength, forces, power) and high-intensity running or jumping actions or investigated the influence of an isolated UB strength training intervention on high-intensity running or jumping performances.

RESULTS

Of the 4730 articles, 7 studies met the inclusion criteria, reporting correlations for 16 high-intensity running or jumping tests. No intervention studies were identified. Preliminary findings of the limited number of studies highlight that greater UB maximal strength-generating capacity may positively influence repeated sprint ability. While a significant moderate correlation between greater absolute UB strength and faster "flying" sprint was also reported, mixed results were found for sprint acceleration. There is also evidence that change-of-direction performance may greatly benefit from high maximal isometric strength of all trunk muscles and that strong trunk extensors may enhance drop jumps.

CONCLUSIONS

This review identifies the potential of UB strength to contribute to high-intensity running and jumping actions. Future research is warranted to investigate this link via various UB strength tests and UB strength training protocols aimed at maximising neuromuscular adaptations.

Frequency and intensity of change of directions in German Bundesliga soccer

The aim of this study was to investigate the change of direction (COD) frequencies and intensities of high-performance soccer players of the German Bundesliga independent of tactical and match context. COD data were collected from 18 German Bundesliga soccer teams (season 2016-2017; 308 fixtures) by an optical tracking system (OTS) (TRACAB). CODs were tracked using a modified algorithm and were sub-categorized by entry velocity (<3.0 m⋅s-1, 3.0-5.5 m⋅s-1, 5.5-7.0 m⋅s-1 and >7.0 m⋅s-1) and COD angle (20-59°, 60-119° and 120-180°). COD metric frequencies were compared between playing positions (goalkeepers, centre backs, full-backs, central midfielders, wide midfielders, and strikers). In general, regardless of entry velocity or COD angle, central midfielders consistently executed the highest number of COD actions during matches compared to the other playing positions. About ≈ 55% and ≈ 38% of CODs were <3.0 m⋅s-1 and <5.5 m⋅s-1, whereas ≈ 7% were >5.5 m⋅s-1. The distribution of COD angle types was ≈ 5% for 20-59°, ≈25% 60-119° and ≈ 70% for 120-180° COD angles. Our data provide insights into the COD demands of high-performance soccer in the German Bundesliga in terms of entry velocity and COD angles and their combination based on a large dataset of OTS data, which provides insights to facilitate the development of physical conditioning strategies, position-specific external load management, and multidirectional speed training with adequate test battery selection and return-to-play protocols for soccer players.

Musculoskeletal Soreness Location and Intensity in Soccer Athletes Across Multiple Seasons

OBJECTIVE

To compare soreness location and intensity between male and female soccer athletes across 2 competitive seasons.

DESIGN

Descriptive Cohort Study.

SETTING

Collegiate Sports Medicine Facility.

PARTICIPANTS

Forty male and 42 female collegiate soccer athletes.

INTERVENTION

Season-long soccer trainings and games.

MAIN OUTCOME MEASURES

Athletes reported perceived soreness location and intensity daily. χ2 analysis and linear mixed effect models were used to compare soreness locations and intensities by sex.

RESULTS

Male and female soccer athletes reported similar number of soreness instances, but male soccer athletes reported soreness more frequently at the ankle, foot, hip, pelvis, and posterior thigh. Female soccer athletes reported soreness more frequently at the anterior leg, anterior thigh, and knee. There was no significant difference in soreness intensity between sexes at any body location (P = 0.86). When collapsed across sex, the frequency of anterior thigh soreness was higher at preseason (7.49%, CI: 5.46-9.52) than at midseason (4.55%, CI: 2.52-6.57; t = -2.94, P = 0.023) and at postseason (3.00%, CI: 0.76-5.23; t = -3.74, P < 0.001). There was also a significant difference in hip soreness frequency between the preseason (2.35%, CI: 1.32-3.33) and the postseason time points (0.52%, CI: -0.73% to 1.67%; t = -2.68, P = 0.023).

CONCLUSIONS

Male and female athletes differ in the locations of their lower extremity soreness. However, lower extremity soreness intensity does not differ between sexes. Soccer athletes report soreness more frequently during the preseason and midseason than during the postseason. With tools to measure daily soreness location and intensity, clinicians could create targeted interventions to reduce soreness and limit its negative affect.

Secondary injury prevention reduces hamstring strain and time-loss groin injury burdens in male professional football

OBJECTIVES

This study aimed to assess the effectiveness of a systems-based secondary injury prevention intervention aimed at early detection and management of hamstring strain injury (HSI) and time-loss groin injury in an Australian male professional football club.

DESIGN

Prospective cohort study.

SETTING

Australian male professional football club.

PARTICIPANTS

Data were collected from male professional football players (n = 73) from a single football club.

MAIN OUTCOME MEASURES

Unilateral knee flexion and side-lying hip adduction maximum voluntary isometric contractions were monitored routinely in-season, two days post-match (≥40 h [h]) during a three-season intervention period. Strength reductions greater than the tests' minimal detectable change percentage prompted intervention. HSI and time-loss groin injury burdens were calculated per 1000 player hours and compared with those from an immediately preceding two-season control period, to assess the effectiveness of the intervention.

RESULTS

Across the intervention period, there was a decrease in HSI (4.98 days absence/1000 h (19.8%) decrease) and time-loss groin injury burdens (0.57 days absence/1000 h (49.1%) decrease) when compared with the control period.

CONCLUSIONS

A systems-based secondary injury prevention intervention shows preliminary positive findings in reducing HSI and time-loss groin injury burdens within a male professional football club, compared with usual care only.

Precise instruction and consideration of the vertical and horizontal force component increases validity and reliability of the 90:20 Isometric Posterior Chain Test

Hamstring injuries are associated with decreased hamstring strength. Matinlauri et al.'s 90:20 Isometric Posterior Chain Test (90:20 IPCT) efficiently assesses hamstring strength, but has not been validated so far. Furthermore, their rather unprecise original instruction allows high variability in test execution. We added a new instruction and variables and examined, whether this measure leads to increased reliability and validity. We assessed hamstring strength of 23 sport students via the 90:20 IPCT under the original instruction, to exert vertical force, and our new instruction, to exert vertical and horizontal force. Instead of only using bare vertical force as variable under the original (Fz_V) and our new instruction (Fz_VH), we also calculated the resultant force (Fres_VH) and the applied torque onto the force place (M_F_ortho_VH). To test for validity, we correlated the outcome variables with peak torque of gold standard dynamometry. Furthermore, we measured muscle activities of the mm. rectus femoris, biceps femoris, semitendinosus, and gluteus maximus under our new instruction and compared them to those under the original variable (Fz_V) via one sample t-tests. To evaluate reliability, tests were repeated on two separate days, for which we calculated intra class correlation coefficients (ICCs) and coefficients of variation (CVs). Our new instruction and variables (Fz_VH, Fres_VH, M_F_ortho_VH) showed better validity (mean r = 0.77, r = 0.81, and r = 0.85) and equally good or better reliability (ICCs: 0.87, 0.89, and 0.94; CVs: 4.7%, 4.1%, and 4.7%) than the original instruction and variable (Fz_V) (mean r = 0.70; ICC: 0.91; CV: 5.6%). There were no differences in muscle activities between the variables and instructions of the 90:20 IPCT. We recommend our new instruction and the applied torque onto the force plate as it makes the 90:20 IPCT a more reliable and valid tool to assess hamstring strength.

The Impact of a Congested Match Schedule (Due to the COVID-19 Lockdown) on Creatine Kinase (CK) in Elite Football Players Using GPS Tracking Technology

The aim was to analyse the consequences of a congested schedule (due to the COVID-19 lockdown) on creatine kinase (CK) in elite football players using GPS tracking technology. A total of 17 elite football players were monitored in training and competition with a global positioning system. Variables including total distance, high-intensity distance, and distance acceleration and deceleration were analysed. Different measurements of serum creatine kinase (CK) concentration were performed on match day (MD) and at 24 h (MD+1), 48 h (MD+2), and 72 h (MD+3) after each match to study the muscle damage of each individual player caused during the match. The results showed a significant increase in physical demands in training (in relative terms regarding the match) at MD+3 compared to MD+1 and MD+2. Furthermore, at +72 h, CK decreases to a value almost the same as that before MD. On the other hand, the players with lower demands for high-intensity actions in the match showed a higher reduction in the concentration of CK at MD+3 compared to MD+1 and MD+2 (p < 0.05). It became evident that players with high-intensity demand and a high number of accelerations and decelerations need more time to assimilate the match load and can remain in a state of muscle fatigue for up to 3 days. In addition, a congested schedule can lead to a state of chronic fatigue in elite football players, limiting physical performance and possibly increasing the potential risk of injury for football players.

Match-related fatigue in basketball: A systematic review

This study aimed to systematically review fatigue responses following basketball match-play and during congested match schedules, considering performance, physiological, athlete-reported, and sleep-related outcomes. Relevant articles published until 23 January 2024 were searched using Scopus, Web of Science, and SPORTDiscus. After screening, 44 studies were included in the systematic review. The main findings indicate that, in most cases, vertical jumping and linear sprinting showed significant decrements at match-end (<1 hour post-match) compared to pre-match [small-to-very large effect sizes (ES)], with persistent (≥1 hour post-match) impairments lasting 24-48 hours in jumping (only in males, small-to-very large ES) and linear sprinting (moderate-to-very large ES). Physiological changes generally included significant increases (moderate-to-very large ES) in cortisol and nutrient metabolism markers at match-end, alongside persistent increases in muscle damage (mainly at 13-72 hours post-match) and inflammation (13-48 hours). Finally, match-play generally increased muscle soreness (mainly at 24-48 hours, moderate-to-very large ES) and perceived fatigue (mainly at match-end), with unclear effects on mood, and no apparent impact on sleep-related outcomes. Research assessing congested match schedules is limited, although possible worsening in muscle damage, inflammation, perceived fatigue and well-being were observed in male players. Overall, these findings indicate an impairment in some of the reviewed performance, physiological, and athlete-reported outcomes.

Football Movement Profile-Based Creatine-Kinase Prediction Performs Similarly to Global Positioning System-Derived Machine Learning Models in National-Team Soccer Players

PURPOSE

The relationship between external load and creatine-kinase (CK) response at the team/position or individual level using Global Positioning Systems (GPS) has been studied. This study aimed to compare GPS-derived and Football Movement Profile (FMP) -derived CK-prediction models for national-team soccer players. The second aim was to compare the performance of general and individualized CK prediction models.

METHODS

Four hundred forty-four national-team soccer players (under 15 [U15] to senior) were monitored during training sessions and matches using GPS. CK was measured every morning from whole blood. The players had 19.3 (18.1) individual GPS-CK pairs, resulting in a total of 8570 data points. Machine learning models were built using (1) GPS-derived or (2) FMP-based parameters or (3) the combination of the 2 to predict the following days' CK value. The performance of general and individual-specific prediction models was compared. The performance of the models was described by R2 and the root-mean-square error (RMSE, in units per liter for CK values).

RESULTS

The FMP model (R2 = .60, RMSE = 144.6 U/L) performed similarly to the GPS-based model (R2 = .62, RMSE = 141.2 U/L) and the combination of the 2 (R2 = .62, RMSE = 140.3 U/L). The prediction power of the general model was better on average (R2 = .57 vs R2 = .37) and for 73% of the players than the individualized model.

CONCLUSIONS

The results suggest that FMP-based CK-prediction models perform similarly to those based on GPS-derived metrics. General machine learning models' prediction power was higher than those of the individual-specific models. These findings can be used to monitor postmatch recovery strategies and to optimize weekly training periodization.

Testing in Intermittent Sports-Importance for Training and Performance Optimization in Adult Athletes

ABSTRACT

Performance in intermittent sports relies on the interplay between multiple physiological systems determining the capacity to perform short explosive efforts as well as repeated intense actions with limited recovery over the course of an entire game. Testing should reflect these demands to allow for sport- and position-specific capacity analyses that eventually may translate into optimized training and improved performance. This may include individual load management and optimized training prescription, intensity targeting for specific positions or individual athletes, as well as benchmarking for monitoring of training progression and enhanced engagement of athletes. This review provides an overview of available tests in different exercise domains identified as relevant (from assessment of single explosive actions to intermittent endurance capacity), forming the basis for recommendations on how to compose a comprehensive yet feasible test battery that may be integrated into the seasonal competition and training plan. The test procedures should cover the performance spectrum of relevance for the individual athlete-also in team sports to account for positional differences. We emphasize the benefits of sport-specific tests, highlight parameters of importance for test standardization, and discuss how the applied test battery may be supplemented with secondary tests directed toward specific energy systems to allow for more in-depth analyses when required (e.g., in terms of an underperforming athlete). The synergy between testing and tracking of match performance (utilizing time-motion or global positioning systems) is highlighted, and although tracking cannot substitute for testing, combining the tools may provide a comprehensive overview of the physiological demands and performance during competition contextualized to the athletes' maximal exercise capacity.

Using Bar Velocity to Assess Post-match Neuromuscular Fatigue in Young Soccer Players

This study aimed to investigate the recovery of neuromuscular performance using mechanical parameters collected during jump (vertical and horizontal) and strength-power exercises in youth soccer players after official soccer matches. Twenty-one outfield highly trained youth male soccer athletes (age: 18.23±0.73 years; weight: 72.12±6.99 kg; height: 1.78±0.08 m) from two teams competing in the 1st division of U-19 Portuguese National Championship participated in this study. Players completed a battery of physical tests at -2 h, + 30 min, +24 h, and +48 h in relation to the match. Countermovement jump height, horizontal jump distance, and bar velocity during the half squat, bench press, and hip thrust exercises, at fixed loads, were recorded. Countermovement jump was impaired until 24 h post-match (-: 1.7% from pre- to 24 h post-match, p=0.050; ES=-: 0.82). Half-squat bar velocity was reduced immediately following the match (-: 6.8% from pre-match, p=0.004; ES=-: 0.64) but recovered at +24 h (+2.9%, p=1.00; ES=0.02). Hip-thrust bar velocity was reduced for up to 48 h post-match (-: 7.4% from pre- to 48 h post-match, p<0.001; ES=-: 0.80). No impairments were found in the horizontal jump and bench press at any moment. Our findings show prolonged decrements in strength of the posterior chain following a soccer match, measured in the hip thrust exercise, while the other exercises displayed faster recovery dynamics.

Creatine kinase concentration on the second post-match day is not associated with risk of subsequent muscle injury in professional football players: a four-season cohort study

OBJECTIVE

The objective of this study was to examine the relationship between creatine kinase (CK) concentration following official matches and the risk of subsequent muscle injury in professional male football (soccer) players.

METHODS

Blood samples were collected on the second post-match day for CK analysis over four consecutive seasons in a professional football club. Players were then followed for five days to observe any occurrence of indirect muscle injury (structural or functional in nature). Players exposed to at least 45 minutes in two consecutive matches within seven days were considered valid cases for analysis.

RESULTS

Eighty players participated in the study, generating 1,656 cases eligible for analysis, of which 229 resulted in muscle injuries. The hamstrings were the most frequently injured muscle group (54%), followed by the adductor (21%), triceps surae (19%), quadriceps (5%), and psoas (1%). While CK concentration was higher in muscle injury cases [783 ± 507 U/L (95%CI, 717 to 849; min-max, 105-2,800)] compared with uninjured cases [688 ± 446 U/L (95%CI, 665 to 711; min-max, 100-2,950)], it was not an accurate predictor of subsequent muscle injury risk in professional football players (sensitivity = 56%; specificity = 55%; odds ratio = 1.00; area under curve = 0.557).

CONCLUSION

CK concentration on the second post-match day cannot be used to effectively screen subsequent muscle injury risk in professional male football players.

Does Total Playing Time Affect the Neuromuscular, Physiological, and Subjective Recovery of Futsal Players during a Congested Period?

The aims of this study were to analyze the effects of a congested period (three games in four days) on countermovement (CMJ) jump-landing metrics, heart rate variability (HRV), and total recovery quality (TQR) score in under-19 male futsal players, and to detect the differences between those who played for more minutes (HIGHMIN) and less minutes (LOWMIN). Fourteen youth futsal players (age: 17.5 ± 0.5 years; body mass: 70.2 ± 8.5 kg; height: 1.80 ± 0.1 m) participated. HRV, TQR questionnaire, and CMJ metrics (i.e., CMJ height, relative peak power (PPREL), eccentric and concentric impulse, braking time, and time to peak force) were registered. A linear mixed model and effect sizes (ESs) were used to assess the differences between groups and days. Considering the total sample, a significant decrease was found in the PPREL and TQR score (p = 0.001-0.013 and ES = 0.28-0.99) on Days 2, 3, and 4 when compared to Day 1. HIGHMIN group presented a significant decrease in PPREL on Day 3 (p = 0.004; ES: 0.62; 95% CI: 0.39-2.65) when compared to Day 1, and in the TRQ score on Day 3 (p = 0.002; ES: 1.98; 95% CI: 0.18-2.46) and 4 (p = 0.003; ES: 2.25; 95% CI: 0.52-3.38) when compared to Day 1. Non-significant differences were found for the rest of the metrics and in the group LOWMIN. In summary, neuromuscular performance (i.e., CMJ PPREL) and subjective recovery were impaired in players with higher playing minutes during a match-congested period when compared to those with less on-court time.

Sleep architecture of elite soccer players surrounding match days as measured by WHOOP straps

This study aimed to quantify and compare sleep architecture before and after home and away matches in elite soccer players from the English Premier League. Across two seasons, 6 male players (age 28 ± 5 y; body mass 85.1 ± 9.5 kg; height 1.86 ± 0.09 m) wore WHOOP straps to monitor sleep across 13 matches that kicked off before 17:00 h. For each, sleep was recorded the night before (MD-1), after (MD) and following the match (MD +1). Across these 3 days total sleep time (TST), sleep efficiency (SE), sleep disturbances, wake time, light sleep, deep sleep, REM sleep, sleep and wake onsets, alongside external load, were compared. TST was reduced after MD versus MD +1 (392.9 ± 76.4 vs 459.1 ± 66.7 min, p = 0.003) but no differences existed in any other sleep variables between days (p > 0.05). TST did not differ after home (386.9 ± 75.7 min) vs. away matches (401.0 ± 78.3 min) (p = 0.475), nor did other sleep variables (p > 0.05). GPS-derived external load peaked on MD (p < 0.05). In conclusion, despite reduced TST on MD, sleep architecture was unaffected after matches played before 17:00 h, suggesting sleep quality was not significantly compromised.

The Effect of Eccentric or Isometric Training on Strength, Architecture, and Sprinting across an Australian Football Season

PURPOSE

This study aimed to investigate the effect of an isometric (ISO) or Nordic hamstring exercise (NHE) intervention, alongside a sprint training program on hamstring strength, architecture, and sprinting performance in Australian footballers.

METHODS

Twenty-five male athletes undertook NHE ( n = 13) or ISO ( n = 12) training across a 38-wk period (including preseason and in season). Biceps femoris long head (BFlh) architecture, ISO, and eccentric knee flexor strength were assessed at baseline, at the end of preseason (14 wk), and at the conclusion of the intervention. Sprint times and force-velocity profiles were determined at baseline and at the end of preseason.

RESULTS

After the intervention, both groups had significant improvements in BFlh fascicle length (NHE: 1.16 cm, 95% CI = 0.68 to 1.63 cm, d = 1.88, P < 0.001; ISO: 0.82 cm, 95% CI = 0.57 to 1.06 cm, d = 1.70, P < 0.001), muscle thickness (NHE: 0.11 cm, 95% CI = 0.01 to 0.21 cm, d = 0.51, P = 0.032; ISO: 0.21 cm, 95% CI = 0.10 to 0.32 cm, d = 0.86, P = 0.002), and eccentric strength (NHE: 83 N, 95% CI = 53 to 114 N, d = 1.79, P < 0.001; ISO: 83 N, 95% CI = 17 to 151 N, d = 1.17, P = 0.018). Both groups also finished the intervention weaker isometrically than they started (NHE: -45 N, 95% CI = -81 to -8 N, d = -1.03, P = 0.022; ISO: -80 N, 95% CI = -104 to -56 N, d = -3.35, P < 0.001). At the end of preseason, the NHE group had improved their 5-m sprint time by 3.3% ± 2.0%), and their maximum horizontal velocity was 3% ± 2.1% greater than the ISO group who saw no changes.

CONCLUSIONS

Both ISO and NHE training with a periodized sprinting program can increase BFlh fascicle length, thickness, and eccentric strength in Australian footballers. NHE training also improves 5-m sprint time and maximum velocity. However, both interventions reduced ISO strength. These findings provide unique, contextually relevant insights into the adaptations possible in semiprofessional athletes.

Female Athletes and the Menstrual Cycle in Team Sports: Current State of Play and Considerations for Future Research

Over the past ten years there has been a dramatic rise in female sport participation and accompanying female professional national leagues across multiple sports, yet research has not followed suit. Although there are known variations between female and male physiology, training protocols in female sport are predominantly underpinned by research undertaken in male athletes. The hormonal variability experienced by women across the menstrual cycle, as well as the menstrual cycle variability between women, may contribute to the complexity of conducting rigorous physiological studies, leading to a paucity of robust sports-specific research that can be confidently applied to female athletes. Moreover, barriers exist in female sport that potentially limit the ability to conduct research, including the lack of full-time programs and limited resources. Recently, there has been increased interest in the potential effects of fluctuations in the female sex hormones, progesterone and oestrogen, on sport performance across different phases of the menstrual cycle. However, current research evaluating the menstrual cycle and physical performance (such as strength, speed, aerobic fitness, and athletes' perception of their performance) have shown inconsistent results. Additionally, methodological design across studies has shown little consistency, making it difficult to draw firm conclusions, which potentially prevents female athletes optimising their physical and sporting performance. It further impacts coaches and sports science researchers in their ability to provide appropriate training recommendations and educational opportunities. It is important to progress in female athlete research with an understanding of how the unique physiology of female athletes may influence their ability to physically perform in their respective sport, which requires representation in sports science research. This paper will provide an overview on current evidence and limitations within menstrual cycle research and provide considerations and directions for future research in this space within team sports.

Interchangeability of optical tracking technologies: potential overestimation of the sprint running load demands in the English Premier League

PURPOSE

The purpose of this study was to assess the agreement between match-derived running load outputs; total distance (TD), high-speed running (HSR) and sprint distance (SPR) obtained by two optical tracking systems.

METHODS

Data were collected from 31 elite footballers from the first team and under-21 squads of an English Premier League (EPL) football club across three competitive matches. One EPL game (game 2) and one under-21 Premier League game (game 3) were played at the team's home stadium and one EPL game (game 1) at an away venue. All matches were tracked concomitantly using eight colour cameras sampling at 10 Hz (PROZONE®) and six high-definition motion cameras sampling at 25 Hz (TRACAB®).

RESULTS

TD displayed a perfect (r = 0.99) correlation while HSR and SPR displayed very large (r = 0.81 and r = 0.73) correlations between TRACAB® and PROZONE®. Mean biases were 5% for TD, -3% for HSR and 61% for SPR. Between games, mean biases for TD were 6% for game 1, and 5% for game 2 and game 3. For HSR, 9% for game 1, -5% for game 2 and 6% for game 3 and for SPR, 31% for game 1, 71% for game 2 and 84% for game 3.

CONCLUSION

TD and HSR can be interchanged between PROZONE® and TRACAB®, to allow accurate interpretation between the two optical systems. PROZONE® overestimated SPR compared to the TRACAB®, with the magnitude of difference considered meaningful, altering interpretation of historical match outputs, sprint volume trends in the EPL and forecasts of the modern game.

Differences in Situational Patterns During Change of Direction Movements Greater than 90° in Youth Male and Female Soccer Players

Change of direction (COD) maneuvers in soccer create tactical advantages, but also expose the player to an increased risk of injury. COD ability is commonly tested with pre-planned drills including cuts greater than 90°. These tests do not take into consideration positional differences players encounter during games. This case-series study used principal component analysis (PCA) to examine situational differences during COD movements between playing positions in youth soccer games. For each of the four teams included (26 females, 27 males), one game was analyzed using video-analysis. Two independent reviewers identified situational patterns and a PCA was used to examine differences between playing positions. Three principal components explained 89% of the variation in the data and were categorized as the total quantity of CODs, attacking/goal-scoring and defensive reacting types of CODs. One-way ANOVA on the individual principal component (PC) scores showed significant differences (p < 0.05) between centre midfielders, goalkeepers, and centrebacks in the quantity of CODs (PC1), and between wingers and fullbacks and centre backs in attacking/goal-scoring CODs (PC2), whereas PC3 was not different between playing positions. Differences between playing positions suggest that training and testing protocols in soccer could be enhanced to better match the individual and playing position-based needs.

High rate of muscle injury despite no changes in physical, physiological and psychophysiological parameters in a professional football team during a long-congested fixture period

This study aimed to analyse match availability, participation, and muscle injury incidence and to compare the effect of time intervals between matches (3-4 versus 6-7 days) on physical, physiological, and psychophysiological parameters in a professional football team during a prolonged congested fixture period. Thirteen professional male football players (29.2 ± 4.8 years old; 78.5 ± 8.3 kg; 179.3 ± 8.8 cm;) participated. Data were collected during 17 consecutive weeks for 35 official matches separated by an average interval of ≤ 3.5 days. Results showed a player availability of 84.8 ± 16.1% while match participation was 68.8% ± 6.4%. Muscle injury incidence was 19.0/ 1,000 hours of match exposure. These injuries occurred after individual players participated in sequences of 8.3 ± 3.3 consecutive matches with intervals of 3.8 ± 0.8 days. No differences were observed in physical performance or in fatigue-related parameters irrespective of the time interval between matches. A high player availability rate was observed. No differences were observed in physical, physiological, and psychophysiological indices of performance when comparing shorter and longer time intervals between consecutive matches.Prolonged exposure to fixture congestion resulted in an high risk of incurring muscle injury.

Determining the capacity for effort and recovery of the elite soccer players specialized in different playing positions

Background

The capacity for effort and recovery in performance sports can be increased by means of modern methodological strategies. This capacity to recover after intense matches and training helps to determine the performance in soccer. Using the Yumeiho technique will accelerate the exercise capacity recovery of the soccer players specialized in central zone positions.

Methods

The research was conducted with the C.S. Internațional Bălești team, formed of 16 players, aged 19-37 years, divided into two groups: experimental group A, n = 8 with central area players and control group B, n = 8 with players from side zones. Measurement and assessment tests: determining lactic acid level (LAC) in blood; 60 m sprinting speed motor test (ST); anaerobic lactic exercise; Gacon Test for evaluating the aerobic power; VO2max test; Dorgo Test for determining the individual recovery capacity; Sleep Quality and Efficiency Index (PSQI) and sleep duration. Means used in the recovery strategy: easy running, static stretching, cryotherapy; Yumeiho therapy was applied only to group A to accelerate the recovery.

Results

The anaerobic lactic capacity was evaluated by 60 m sprint test at the beginning and the end of the research. The results highlight the increase of the sprinting speed by 0.08 s in group A (p < 0.001). The aerobic capacity evaluated by means of Gacon Test in both groups shows the value 23.7%, namely a well-prepared level (p < 0.001). VO2max value in the soccer players of group A shows 87.5% good aerobic power, while the players of group B have 50% good aerobic power (p < 0.001). The concentration of LAC after exercise has a higher value in group A (p > 0.05). The level of recovery after exercise is improved in both groups, with larger differences in group A (very good level, p < 0.001). The PSQI grew by 20.37% in group A and by 11% in group B. The sleep duration increased in both groups (p < 0.001). The results of the correlation analysis in the soccer players of group A highlight strong connections of 14.8% while in group B the value is 12.5%.

Conclusion

The assessment of effort capacity in soccer players specialized in different playing positions at the beginning and the end of the research highlights the increase of the anaerobic lactic effort and aerobic effort. This assessment also shows the improvement of the individual recovery capacity. A higher PSQI and the increase of sleep duration in both groups, with greater differences of group A were found, which determined their level of capacity for effort and recovery. The use of the Yumeiho technique in the program of post-exercise recovery accelerates the aerobic and anaerobic lactic effort capacity of the soccer players specialized in the central zone positions. It positively influences exercise capacity recovery in general.

Blood Flow Restriction Is Not Useful as Soccer Competition Recovery in Youth Male National-Level Soccer Players: A Crossover Randomised Controlled Trial

In soccer, blood flow restriction (BFR) is used to optimise between-match recovery. However, the benefits are unclear. This study evaluated the effects of BFR as a recovery strategy after a competition on countermovement jump (CMJ) height, rating of perceived exertion (RPE) and the wellness of soccer players. Forty national-level soccer players were allocated into two conditions: BFR (an active recovery session wearing a BFR device, 24 h after a competition) or NoBFR (the same recovery without BFR). CMJ, RPE and wellness were evaluated the day (CMJ and RPE) or the morning (wellness) before the competition; just after the competition (CMJ and RPE); and 24, 48 (wellness) and 72 h later. After 4 weeks, the players changed conditions. All players showed impaired CMJ (p = 0.013), RPE (p < 0.001) and wellness (p < 0.001) after the match compared with the baseline. The CMJ returned to the baseline 24 h later and wellness returned 48 h later. Only in the BFR condition did the RPE remain impaired 24 h after the match, which was also the moment after finishing the BFR recovery session (p < 0.001). BFR during active recovery does not provide any additional benefits compared with traditional exercise modalities to recover CMJ, RPE and wellness in youth national-level soccer players. BFR could even induce an immediate higher RPE.

Association between internal load responses and recovery ability in U19 professional soccer players: A machine learning approach

Background

The objective of soccer training load (TL) is enhancing players' performance while minimizing the possible negative effects induced by fatigue. In this regard, monitoring workloads and recovery is necessary to avoid overload and injuries. Given the controversial results found in literature, this study aims to better understand the complex relationship between internal training load (IL) by using rating of perceived exertion (RPE), recovery, and availability (i.e., subjective players' readiness status).

Methods

In this cross-sectional study, twenty-two-professional soccer players (age: 18.5 ± 0.4 years, height: 177 ± 6 cm, weight: 67 ± 6.7 kg) competing in the U19 Italian Championship were monitored using RPE scale to assess IL, and TreS scale to detect information about recovery and training/match availability during an entire season (2021-2022).

Results

Autocorrelation analysis showed a repeated pattern with 7 days lag (weekly microcycle pattern) for all the variables considered (i.e., TL, recovery, and availability). For recovery (r = 0.64, p < 0.001) and availability (r = 0.63, p < 0.001) the best lag for both of them is 1 day. It indicates that recovery and availability are related to the past day value. Moreover, TL was found to be negatively affected by recovery and availability of the current day (lag = 0 day). Cross-correlation analysis indicates that TL is negatively affected by recovery (r = 0.46, p < 0.001) and availability (r = 0.42, p < 0.001) of the current day (lag = 0 day). In particular, lower recovery and availability will result in following lower TL. Furthermore, we found that TL negatively affects recovery (r = 0.52, p < 0.001) and availability (r = 0.39, p < 0.01) of the next day (lag = 1 day). In fact, the higher the TL in a current day is, the lower the recovery and availability in the next day will be.

Conclusion

In conclusion, this study highlights that there is a relationship between TL and recovery and that these components influence each other both on the same day and on the next one. The use of RPE and TreS scale to evaluate TL and recovery/availability of players allows practitioners to better adjust and schedule training within the microcycle to enhance performance while reducing injury risk.

The Impact of 120 Minutes of Soccer-Specific Exercise on Recovery

Purpose: The extra-time (ET) period of soccer is competed during fixture congested schedules with often limited recovery time between matches. The aim of this study was to assess muscle damage recovery following 90- and 120-min (i.e., incorporation of ET) of simulated soccer match-play. Methods: Twelve semiprofessional soccer players completed 90 and 120-min treadmill-based soccer-specific exercise in a counterbalanced order. Creatine kinase (CK), creatinine, urea, aspartate aminotransferase, perceived muscle soreness, pain pressure threshold, reactive strength index, countermovement jump height, and isokinetic strength assessments of eccentric knee flexors at 60, 180 and 270 deg‧s^-1 were taken at baseline and immediately-, 24, 48 and 72-hr post-exercise to assess recovery. Results: No significant between-trial interactions except for CK were found. Pairwise comparisons detected a 53% increase in CK at 24-hr (455 ± 29 μ∙L^-1) following 120-min of simulated match-play vs. the corresponding post 90-min time-point (299 ± 29 μ∙L^-1; p < .01). The 120-min trial caused a 58% higher CK response at 72-hr (244 ± 25 μ∙L^-1) vs. post 90-min comparisons (154 ± 29 μ∙L^-1; p = .02). No interaction effects were detected for any other recovery variables. Creatine kinase and perceived muscle soreness remained elevated up to 72-hr in both trials (p < .01). Conclusions: These data indicate that 120 min of simulated soccer match-play delays the time-course of CK recovery up to 72-hr post-match. However, 120 min of simulated soccer has no additional impact on functional recovery and perceived muscle soreness vs. 90 min. Recovery should be investigated following 90- and 120-min of actual match-play.Trial registration The study was pre-registered on the Open Science Framework (DOI: 10.17605/OSF.IO/VGU6T Date: 10/06/2019).

Scheduling Concurrent Training 48 versus 72 h after Simulated Match Play: Effects on Neuromuscular Function and Fatigue

INTRODUCTION

Scheduling concurrent training (CT) during the in-season microcycle in field-based team sport is driven by prematch and postmatch recovery. This study examined the neuromuscular function, fatigue, and soreness responses to CT administered 48 h (match day (MD) + 2) versus 72 h (MD + 3) after match.

METHODS

Ten male recreational-level team sport athletes were monitored daily during two 5-d microcycles, which began with a simulated match (Soccer-specific Aerobic Field Test (SAFT90)) and CT performed either 48 or 72 h after match. Maximal voluntary force, quadriceps maximum EMG, voluntary activation, muscle contractile function (evoked twitch responses), muscle soreness, and fatigue were assessed immediately before and after the SAFT90, and every 24 up to 96 h after match. Outcome measures were also assessed immediately after CT. The CT consisted of an intermittent sprint protocol and a lower limb resistance training session separated by 1 h.

RESULTS

Immediately after the SAFT90 in both conditions, maximal voluntary force was below baseline (mean change (Δ), -14.6% ± 10.0%; P = 0.03), recovering 48 h post. Quadriceps contractile function (Δ, -31.5% ± 11.4%; P = 0.003) and voluntary activation (Δ, -8.9 ± 6.2%; P = 0.003) were also hampered after the SAFT90, recovering 24 h post in both conditions. In addition, the SAFT90 elicited elevated levels of fatigue and muscle soreness that recovered 24 h after the SAFT90 before increasing at 72 and 96 h post in the MD + 2 and MD + 3 conditions, respectively.

CONCLUSIONS

Recovery of fatigue was only observed at the end of the microcycle when CT was prescribed on MD + 2. Therefore, CT scheduled early (MD + 2) in the microcycle might avoid compromising forthcoming match preparation.

Seasonal Variation of Physical Performance, Bilateral Deficit, and Interlimb Asymmetry in Elite Academy Soccer Players: Which Metrics Are Sensitive to Change?

ABSTRACT

Bishop, C, Abbott, W, Brashill, C, Loturco, I, Beato, M, and Turner, A. Seasonal variation of physical performance, bilateral deficit, and interlimb asymmetry in elite academy soccer players: Which metrics are sensitive to change? J Strength Cond Res 37(2): 358-365, 2023-This study aimed to report seasonal variations for (a) physical performance, (b) interlimb asymmetry, and (c) bilateral deficit (BLD) data over the course of a competitive soccer season and determine which metrics are sensitive to change. This study used a repeated-measures observational design for 19 under-20, elite, academy, soccer players (age: 17.58 ± 0.61 years; height: 1.81 ± 0.09 m; body mass: 74.36 ± 7.58 kg), who conducted bilateral and single-leg countermovement jumps (CMJ and SLCMJ), linear speed (5, 10, 20, and 30-m) and 505 change of direction (COD) speed tests, at pre, mid, and end of season time points. For jump tests, jump height, reactive strength index modified, time to takeoff, and countermovement depth metrics were monitored, with interlimb asymmetry and the BLD also calculated for each. Significant improvements ( p < 0.05) in performance were evident in all fitness tests: CMJ (effect size [ES]: 0.61 to 1.03), SLCMJ (ES: 0.60 to 2.25), linear speed (ES: -0.54 to -1.96), and COD speed (ES: -0.68 to -1.14). Significant reductions in asymmetry (ES: -0.68 to -1.07) and significant increases in the BLD (ES: 1.15 to 1.57) were also evident throughout the season. Additionally, kappa coefficients were used to determine consistency in limb dominance throughout the season, but only poor to fair levels of agreement (kappa: -0.17 to 0.37) were evident, highlighting the fluctuating nature of limb dominance throughout the season. Despite all tests exhibiting meaningful change, the SLCMJ and linear speed showed the most frequent and largest differences in performance, highlighting their usefulness in the ongoing monitoring process of physical capacities in elite male academy players across a competitive soccer season.

The introduction of the six-again rule has increased acceleration intensity across all positions in the National Rugby League competition

The impact of the six-again rule change on the movement of National Rugby League (NRL) athletes was examined. Player Global Navigation Satellite System (GNSS) data (10 Hz) was collected from 42 athletes who competed in 56 matches across the 2019 to 2021 NRL seasons. Maximal mean speed (m·min^-1) and acceleration (m·s^-2) were established across a 10 s to 10-min duration via raw GNSS files, with subsequent intercept (mean estimates) and slope values determined via power law analysis. The distributions of match distance (m) and impulse (kN·s^-1) were established during ball-in-play time. To determine the significance between positions and seasons under different rules, linear mixed models were used. Effects were described using standardised effect sizes (ES) with 90% confidence limits (CL). Acceleration intercepts (power law-derived) across all positions were substantially greater (>0.6 SD) following the introduction of the six-again rule in the 2020 (mean ± SD; 1.02 ± 0.10 m·s^-2) and 2021 seasons (1.05 ± 0.08 m·s^-2) compared to the 2019 season (0.91 ± 0.07 m·s^-2). Mean acceleration during ball-in-play time was greater in 2020 (ES; 90% CL = 0.75; ± 0.32) compared to 2019. The acceleration requirements of rugby league increased across all positional groups following the modification in NRL competition rules. Practitioners should tailor training programs for athletes to reflect the increased acceleration intensity found under the revised competition format.

The Dose–Response Relationship Between Training-Load Measures and Changes in Force–Time Components During a Countermovement Jump in Male Academy Soccer Players

Purpose: To manage physical performance in soccer, practitioners monitor the training load (TL) and the resulting fatigue. A method frequently used to assess performance is the countermovement jump (CMJ). However, the efficacy of CMJ to detect fatigue from soccer matches and training remains uncertain, as does the relationship between TL and change in CMJ performance. The aims of the present study were 2-fold. One was to observe the changes of CMJ force–time components and jump height (JH). The second was to examine dose–response relationships between TL measures and CMJ over a 6-week preseason. Methods: Twelve male academy soccer players (17 [1] y, 71.2 [5.6] kg, and 178 [5.8] cm) were recruited. Daily changes in CMJ were assessed against baseline scores established before preseason training, along with internal and external TL measures. A series of Bayesian random intercept models were fitted to determine probability of change above/below zero and greater than the coefficient of variation established at baseline. Jumps were categorized into match day minus (MD−) categories where the higher number indicated more time from a competitive match. Results: JH was lowest on MD − 3 (28 cm) and highest on MD − 4 (34.6 cm), with the probability of change from baseline coefficient of variation highly uncertain (41% and 61%, respectively). Changes to force–time components were more likely on MD − 3 (21%–99%), which provided less uncertainty than JH. Bayes R2 ranged from .22 to .57 between TL measures and all CMJ parameters. Conclusions: Force–time components were more likely to change than JH. Practitioners should also be cautious when manipulating TL measures to influence CMJ performance.

Physical match performance and creatine kinase levels in elite football players

Many studies have shown that creatine kinase (CK) concentration increases following an elite-level football competition. However, the relationship between match performance and CK levels at 72 hours after the match is still unclear. The aim of this study was to determine the relationship between physical match performance data and blood CK levels 72 hours post-match in elite football players. The study included 11 male elite football players (age=26.36±3.29 years, height=181.60±6.1 cm, weight=75.41±5.96 kg). Capillary blood samples were collected from the participants approximately 72 hours post-match and examined by reflectance photometry. Physical match performance data from 2 consecutive matches of a Turkish Super League team (while competing in the UEFA Europa League) were collected by a computerized video tracking system. There was no significant correlation between the players’ CK level and their total distance (p=0.6012), high-intensity (20-24 km/h) running distance (p=0.8837), or sprinting distance (p=0.235). CK level was also not correlated with the percentage of total distance covered in high-intensity running (r=-0.62, p=0.052). However, moderate to strong negative correlations were observed between CK level and percentage of total distance covered in sprinting (r=-0.67, p=0.032) and percentage of total distance covered in high-intensity running and sprinting (r=-0.70, p=0.022). The current study suggests the benefit of evaluating distances covered in the game and CK concentrations 72 hours post-match while planning recovery interventions.

Analysis of change of direction performance with dominant and non-dominant leg using linear and nonlinear approaches

This study was aimed to analyse the lower limb kinematics during the change of direction (COD) performance with the dominant (DL) and non-dominant (NDL) leg using linear (traditional kinematics) and nonlinear (Self Organising Map-based cluster analysis) approaches. Three 5-0-5 COD performances with the DL and three with the NDL were performed by 23 (aged 21.6 ± 2.3 years) collegiate athletes. No significant difference was observed between the COD duration, and approach speed of DL and NDL. Significantly greater ankle abductions, knee and hip external rotations were identified in COD with DL, compared to NDL (p < .001, d > 0.8). Self Organising Maps portrayed a completely different coordination pattern profile during change of direction performance with the DL and NDL. The cluster analysis illustrated similar inter-individual coordination patterning when participants turned with their DL or NDL. No visible relationship was observed in the cluster analysis of the lower limb joint angles and angular velocities. Outcomes of this study portrayed that coordination patterning (combination of joint angles and the rate of change of angles) could portray the movement patterning differences in different tasks, while a sole investigation on the joint angles or angular velocities may not reveal the underlying mechanisms of movement patterning.

Effect of a Condensed NBA Season on Injury Risk: An Analysis of the 2020 Season and Player Safety

Background:

Health and safety concerns surrounding the coronavirus 2019 (COVID-19) pandemic led the National Basketball Association (NBA) to condense and accelerate the 2020 season. Although prior literature has suggested that inadequate rest may lead to an increased injury risk, the unique circumstances surrounding this season offer a unique opportunity to evaluate player safety in the setting of reduced interval rest.

Hypothesis:

We hypothesized that the condensed 2020 NBA season resulted in an increased overall injury risk as compared with the 2015 to 2018 seasons.

Study Design:

Descriptive epidemiology study.

Methods:

A publicly available database, Pro Sports Transactions, was queried for injuries that forced players to miss ≥1 game between the 2015 and 2020 seasons. Data from the 2019 season were omitted given the abrupt suspension of the league year. All injury incidences were calculated per 1000 game-exposures (GEs). The primary outcome was the overall injury proportion ratio (IPR) between the 2020 season and previous seasons. Secondary measures included injury incidences stratified by type, severity, age, position, and minutes per game.

Results:

A total of 4346 injuries occurred over a 5-season span among 2572 unique player-seasons. The overall incidence of injury during the 2020 season was 48.20 per 1000 GEs but decreased to 39.97 per 1000 GEs when excluding COVID-19. Despite this exclusion, the overall injury rate in 2020 remained significantly greater (IPR, 1.42 [95% CI, 1.32-1.52]) than that of the 2015 to 2018 seasons (28.20 per 1000 GEs). On closer evaluation, the most notable increases seen in the 2020 season occurred within minor injuries requiring only a 1-game absence (IPR, 1.53 [95% CI, 1.37-1.70]) and in players who were aged 25 to 29 years (IPR, 1.57 [95% CI, 1.40-2.63]), averaging ≥30.0 minutes per game (IPR, 1.67 [95% CI, 1.47-1.90]), and playing the point guard position (IPR, 1.67 [95% 1.44-1.95]).

Conclusion:

Players in the condensed 2020 NBA season had a significantly higher incidence of injuries when compared with the prior 4 seasons, even when excluding COVID-19–related absences. This rise is consistent with the other congested NBA seasons of 1998 and 2011. These findings suggest that condensing the NBA schedule is associated with an increased risk to player health and safety.

Monitoring the post-match neuromuscular fatigue of young Turkish football players

Neuromuscular fatigue tests have been used in previous studies to organize post-match training programs and to minimize injuries. The aim of this study is to describe the neuromuscular fatigue that occurs after a football match and to examine the relationship between internal and external load values in the match and fatigue parameters obtained at different time intervals. Twenty male U19 academy league soccer players (age: 19; height: 181.3 ± 4.3; weight: 73.4 ± 6.7) participated in the study. The countermovement jump (CMJ) test was applied to the players 24 h before, as well as 24, 48, 72, 96, and 120 h after a football match. During the CMJ tests, the maximum velocity of each player during the jump was recorded by using the GymAware linear position transducer. The CMJ maximum velocity values 24 h before and 24 h after the match, as well as the CMJ height values (Cohen's d: 1.210; p < 0.001), were statistically different from the values recorded 24 h before and 24 and 48 h after the match (Cohen's d: 1.578; p < 0.001; Cohen's d: 0,922; p < 0.009). The correlation values were not statistically significant. The results suggest, CMJ height and CMJ maximum velocity values, which determine neuromuscular fatigue after a football match, can be used by practitioners to display post-match neuromuscular fatigue measurements.

What are the significant turning demands of match play of an English Premier League soccer team?

This study aimed to compare the significant turning demands of English Premier League soccer match play relative to playing position using LiDAR technology. Turning data were collected from an English Premier League soccer team (2020-2021 season; 18 fixtures) using a Sportlight® LiDAR tracking system. Turns were tracked during match play, sub-categorised by entry speed (<3.0, 3.0-5.5, 5.5-7.0 and >7.0 m/s) and turning angle (Low: 20-59°; Medium: 60-119°; High: 120-180°). Turning metric frequencies were compared between playing positions (centre backs, full-backs, central midfielders, wide midfielders, and central forwards). On average, per match, central midfielders performed more total turns (~38 vs ~18-27), turns with entry speeds <3.0 (~15 vs ~7-10) and 3.0-5.5 m/s (~21 vs ~8-15) and low (~4 vs ~1-2), medium (~10 vs ~3-6) and high angled turns (~24 vs ~12-18) compared to all other playing positions (p ≤ 0.001, d = 0.96-2.74). Approximately, 90% of turns during matches were performed with entry speeds <5.5 m/s and ~63-70% were high angled turns. This study provides unique insights into the turning demands of English Premier League soccer matches , which can be used to inform position-specific physical preparation strategies, turning testing battery selection, agility drill construction, and rehabilitation and return to play standards.

Monitoring Psychometric States of Recovery to Improve Performance in Soccer Players: A Brief Review

In order to maximize adaptations and to avoid nonfunctional overreaching syndrome or noncontact injury, coaches in high-performance sports must regularly monitor recovery before and after competitions/important training sessions and maintain well-being status. Therefore, quantifying and evaluating psychometric states of recovery during the season in sports teams such as soccer is important. Over the last years, there has been substantial growth in research related to psychometric states of recovery in soccer. The increase in research on this topic is coincident with the increase in popularity obtained by subjective monitoring of the pre-fatigue state of the players before each training sessions or match with a strong emphasis on the effects of well-being or recovery state. Among the subjective methods for players’ control, the Hooper index (HI) assesses the quality of sleep during the previous night, overall stress, fatigue, and delayed-onset muscle soreness. Additionally, the total quality of recovery (TQR) scale measures recovery status. The HI and TQR recorded before each training session or match were affected by the variability of training load (TL) and influenced the physical and technical performances, and the affective aspects of soccer players. Researchers have recommended wellness monitoring soccer players’ psychometric state of recovery before each training session or match in order to detect early signs of fatigue and optimize high-level training performance. This method allows for better detecting signs of individual fatigue and allows coaches to adapt and readjust the TL, and avoid physical and technical gaps in order to improve the performance of soccer players.

Acceleration and deceleration demands during training sessions in football: a systematic review

PURPOSE

The aim of this review is to summarize the current scientific knowledge about acceleration and deceleration demands during football training.

METHODS

A systematic search of three electronic databases (PubMed, SPORTDiscus, Web of Science) was performed to identify peer-reviewed relevant English-language articles, following PRISMA guidelines.

RESULTS

All acceleration and deceleration data were analyzed and organized into four categories: i) training drills variables (i.e. manipulated drills variables such as number of players in small-sided games), ii) training exercises (i.e. different drills such small games or circuit training), iii) players' positions (i.e. demands for each playing position) and iv) training schedule (i.e. training sessions presented as microcycles, season sections or full season). Full-text articles of 42 studies were included in the final analysis. Players' level included: amateur, youth, semi-professional, professional and elite players. All playing positions were considered, including goalkeepers. Six different global position systems brands were used, with the majority measuring data at 10 Hz. Different thresholds and intensities were used in several papers. Lower acceleration and deceleration intensities occurred more often than higher intensities in all four categories.

CONCLUSION

Different exercises elicit different demands and small-sided games presented higher acceleration and deceleration demands than circuit training and other running based drills. Furthermore, manipulating drills variables, as reducing or increasing number of players in small-sided games increase or decrease demands, respectively. Additionally, wide playing positions, such as fullbacks, are generally exposed to higher acceleration and deceleration demands. From a planning point of view, acceleration and deceleration demands decrease as match day approaches.

Etiology and Recovery of Neuromuscular Function Following Academy Soccer Training

Aim: To profile the etiology and recovery time-course of neuromuscular function in response to a mixed-content, standard training week in professional academy soccer players. We concurrently examined physical performance, cognitive function, and perceptual measures of mood and wellness states to identify a range of simple tests applied practitioners could use in the field as surrogate measures of neuromuscular function.

Methods: Sixteen professional academy soccer players completed a range of neuromuscular, physical, perceptual, mood, and cognitive function tests at baseline and after a strenuous training day (pitch and gym), with retest at 24, 48, and 72 h, and further pitch and gym sessions after 48 h post-baseline. Maximal voluntary contraction force (MVC) and twitch responses to electrical stimulation (femoral nerve) during isometric knee-extensor contractions and at rest were measured to assess central nervous system (voluntary activation, VA) and muscle contractile (potentiated twitch force, Q_tw,pot) function.

Results: Strenuous training elicited decrements in MVC force post-session (−11%, p = 0.001) that remained unresolved at 72 h (−6%, p = 0.03). Voluntary activation (motor nerve stimulation) was reduced immediately post-training only (−4%, p = 0.03). No change in muscle contractile function (Q_tw,pot) was observed post-training, though was reduced at 24 h (−13%, p = 0.01), and had not fully recovered 72 h after (−9%, p = 0.03). Perceptions of wellness were impaired post-training, and recovered by 24 h (sleepiness, energy) and 48 h (fatigue, muscle soreness, readiness to train). Countermovement jump performance declined at 24 h, while RSI (Reactive Strength Index) decrements persisted at 48 h. No changes were evident in adductor squeeze, mood, or cognitive function.

Conclusion: Elite youth soccer training elicits substantial decrements in neuromuscular function, which are still present 72 h post-strenuous exercise. Though central processes contribute to post-exercise neuromuscular alterations, the magnitude and prolonged presence of impairments in contractile function indicates it is the restitution of muscular function (peripheral mechanisms) that explains recovery from strenuous training in academy soccer players.

Bilateral vs. Unilateral Countermovement Jumps: Comparing the Magnitude and Direction of Asymmetry in Elite Academy Soccer Players

ABSTRACT

Bishop, C, Abbott, W, Brashill, C, Turner, A, Lake, J, and Read, P. Bilateral vs. unilateral countermovement jumps: comparing the magnitude and direction of asymmetry in elite academy soccer players. J Strength Cond Res 36(6): 1660-1666, 2022-The aims of this study were to compare the magnitude and direction of asymmetry in comparable bilateral and unilateral countermovement jumps (CMJs). Forty-five elite academy soccer players from under-23 (n = 15), under-18 (n = 16), and under-16 (n = 14) age groups performed bilateral and unilateral CMJs as part of their routine preseason fitness testing. For the magnitude of asymmetry, no significant differences were evident for any metric between tests. However, the eccentric impulse asymmetry was significantly greater than mean force and concentric impulse in both bilateral and unilateral tests (p < 0.01). For the direction of asymmetry, Kappa coefficients showed poor levels of agreement between test measures for all metrics (mean force = -0.15, concentric impulse = -0.07, and eccentric impulse = -0.13). The mean jump data were also presented relative to the body mass for each group. For the bilateral CMJ, significant differences were evident between groups but showed little consistency in the same group performing better or worse across metrics. For the unilateral CMJ, eccentric impulse was the only metric to show meaningful differences between groups, with the under-18 group performing significantly worse than under-23 and under-16 players. This study highlights that despite the magnitude of asymmetry being similar for each metric between comparable bilateral and unilateral CMJs, consistency in the direction of asymmetry was poor. In essence, if the right limb produced the larger force or impulse during a bilateral CMJ, it was rare for the same limb to perform superior during the unilateral task. Thus, practitioners should be aware that bilateral and unilateral CMJs present different limb dominance characteristics and should not use 1 test to represent the other when measuring between-limb asymmetries.

Patellofemoral Pain Syndrome in Young Female Athletes: A Case-Control Study

BACKGROUND

Patellofemoral pain syndrome (PFPS) is the most common cause of anterior knee pain in children and adolescents, and it is characterized by highly limiting, recurrent, frontal pain.

OBJECTIVES

The purpose of the study is to assess the incidence and onset of PFPS in the young female athletes and to compare it to healthy individuals.

METHODS

Between 2017 and 2019, 51 subjects were reviewed and divided in three groups: rhythmic gymnastics athletes (RG; 21 individuals, mean age: 13.8 ± 3.6 years), basketball athletes (BG; 17 individuals, mean age: 14.2 ± 3.1 years), and control group (CG; 13 individuals, mean age: 14.5 ± 4.3 years). All patients underwent physical examination including patellar glide, tilt, grind and apprehension tests, tiptoe and jack tests, Coleman block, and navicular drop tests. The clinical and functional outcomes of the subjects were assessed using the Kujala patellofemoral score (KPS).

RESULTS

In RG patients were recorded 66.7% of normal footprint (NF), 9.5% of cavus feet (FCF), and 23.8% of flatfeet (FFF); 14.8% patellar positive tests, KS = 98.6 ± 13.7. BG patients had 70.6% of NF, 11.8% FCF, and 17.6% of FFF; 23.5% patellar positive tests, KS = 98.3 ± 12.4. CG patients had 61.5% of NF, 7.7% of FCF and 30.8% of FFF; 15.4% patellar positive tests, KPS = 98,9 ± 15.3. No statistically significance was found between the three cohorts of patients.

CONCLUSIONS

PFPS is a common pathology; muscular imbalance and overuse could exacerbate pain and discomfort in young female athletes. Our findings show high type and level of sport activity are not related to increase frequency of clinical symptoms related to PFPS.

Magnitude or Direction? Seasonal Variation of Interlimb Asymmetry in Elite Academy Soccer Players

ABSTRACT

Bishop, C, Read, P, Chavda, S, Jarvis, P, Brazier, J, Bromley, T, and Turner, A. Magnitude or direction? Seasonal variation of interlimb asymmetry in elite academy soccer players. J Strength Cond Res 36(4): 1031-1037, 2022-Previous research has highlighted a distinct lack of longitudinal data for asymmetry. The aims of this study were to provide seasonal variation data for the magnitude and direction of asymmetry. Eighteen elite male academy soccer players (under-23) performed unilateral countermovement jumps (CMJs) and unilateral drop jumps (DJs) during pre-season, mid-season, and end of season time points. Recorded metrics for asymmetry included jump height and concentric impulse for the CMJ, and jump height and reactive strength index for the DJ. The magnitude of asymmetry showed trivial to small changes throughout the season (CMJ effect size [ES] range = -0.43 to 0.05; DJ ES range = -0.18 to 0.41). However, Kappa coefficients showed poor to substantial levels of agreement for the direction of asymmetry during the CMJ (Kappa = -0.06 to 0.77) and DJ (Kappa = -0.10 to 0.78) throughout the season. These data show that when monitoring asymmetry, the magnitude alone may provide a false impression of consistent scores over time. By contrast, monitoring the direction of asymmetry highlights its task and variable nature and is suggested as a useful tool for practitioners who wish to monitor asymmetry over the course of a competitive soccer season.