Preseason neuromuscular versus endurance training leads to greater improvements in isokinetic strength, muscle damage, and inflammation parameters in highly trained female soccer players

BACKGROUND

The preseason offers an opportunity to achieve an optimal level of physical fitness for the entire season. The question arises whether the training programs induce muscle damage and inflammatory processes which may have a negative impact on players' readiness at the beginning of the season.

OBJECTIVES

To examine the effects of a preseason neuromuscular training program (NMT) versus endurance training (ET) on measures of isokinetic strength, muscle damage, and blood parameters in female soccer players.

METHODS

Twenty-two highly trained female soccer players with a mean age of 17.0 ± 1.3 years were randomly assigned to a NMT (n = 11) or ET group (n = 11). NMT and ET programs lasted six weeks with three sessions per week, each 45-60 min. NMT included strength, power, linear sprint and change-of-direction speed, and dynamic stability exercises. ET comprised running, circuit drills, coordination, aerobic circuit, interval-training, speed-endurance exercises, and dynamic stretching. isokinetic knee flexor/extensor parameters (e.g., peak torque) were tested pre- and post-training. Blood samples were analyzed for muscle damage markers: creatine kinase (CK), lactate dehydrogenase (LDH), and inflammation markers: C-reactive protein (CRP), and interleukin-6 (IL-6).

RESULTS

Significant group-by-time interactions were found for all isokinetic parameters (0.001 < p < 0.012, 1.35 < d < 4.17). Post-hoc tests revealed significant improvements following NMT but not ET (0.001 < p < 0.045, 0.81 < d < 2.46). Additionally, there were also significant group-by-time interactions for IL-6 (p = 0.005; d = 0.31), CK (p = 0.026; d = 1.0), and LDH (p < 0.003; d = 1.44). Variations in IL-6, CK, and LDH determined by post-hoc tests indicated decreases in NMT but not ET (IL-6: p = 0.005, d = 1.27; CK: p = 0.023, d = 1.01; LDH: p = 0.002, d = 1.42).

CONCLUSIONS

Six weeks of preseason NMT produced larger improvements in isokinetic strength and less muscle damage and inflammation in highly-trained female soccer players compared to ET group.

Neuromuscular fatigue in English Premier League academy football players: Within- and cross-season responses

OBJECTIVES

To examine the within- and cross-season neuromuscular fatigue responses in English Premier League U-18 academy football players.

DESIGN

Twenty-five players from the same team completed weekly countermovement jump and isometric adductor and posterior chain strength tests for a full competitive season.

METHODS

Global positioning system measures of training and match total, high-metabolic load and sprint distance were recorded daily and converted into exponentially weighted moving average seven- and twenty-eight-day values.

RESULTS

TD28 (p < .001), HML28 (p < .001), and SD28 (p = .002) shared negative relationships with countermovement jump height, but there was no main cross-season effect (p = .137). TD28 (p = .016) and HML28 (p = .012) positively related to isometric posterior chain strength but there was no effect of SD28 (p = .653), SD7 (p = .549), TD7 (p = .080) or HML7 (p = .104). Cross season, isometric posterior chain strength followed a curvilinear response whereby performance increased across the beginning of the season and decreased towards the end of the season (p = .003). There was no effect of training load or time on isometric adductor strength performance (p > .094).

CONCLUSIONS

Neuromuscular status, signalled by countermovement jump height changes fluctuates across the season in response to sustained changes in training and match load, but there is no evidence of a main cross-season linear effect. Total training and match volume exert moderating effects on the internal training load dose, and in-turn, important moderating effects on neuromuscular fatigue, particularly when composed of high volumes of high-intensity and sprint distances. The posterior chain might be particularly susceptible to fatigue towards the end of the season.

Construction of 2022 Qatar World Cup match result prediction model and analysis of performance indicators

This research investigates the influence of performance metrics on match outcomes and constructs a predictive model using data from the Qatar World Cup. Employing magnitude-based decision and an array of machine learning algorithms, such as Decision Trees, Logistic Regression, Support Vector Machines, AdaBoost, Random Forests, and Artificial Neural Network, we examined data from 59 matches, excluding extra time. Fourteen performance indicators were integrated into the model, with two types of match outcomes-winning and non-winning-serving as the output variables. The ANN model exhibited the highest predictive performance, achieving an accuracy of 75.42%, an AUC of 76.96%, a precision of 72.73%, a recall of 65.31%, a specificity of 77.03%, and an F1 score of 68.82%. SHAP analysis revealed that "On Target", "Shooting Opportunity", and "Ball Progressions" were the most influential features. These findings underscore the critical role of shooting accuracy and the creation of scoring opportunities in determining match outcomes. Consequently, this study developed an accurate model for predicting match outcomes and meticulously analyzed the match performance. Coaches should prioritize the sensitive indicators identified in this study during training and structure training sessions accordingly.

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.

The Effect of Combined Transcranial Direct Current Stimulation and Pneumatic Compression as Part of a Comprehensive Recovery Strategy in Professional Male Top-Level Soccer Players

ABSTRACT

Gonçalves, DS, Moscaleski, LA, da Silva, GM, Morgans, R, Okano, AH, and Moreira, A. The effect of combined transcranial direct current stimulation and pneumatic compression as part of a comprehensive recovery strategy in professional male top-level soccer players. J Strength Cond Res 38(9): 1658-1666, 2024-This retrospective study aimed to examine the effect of transcranial direct current stimulation (tDCS) combined with lower limb pneumatic compression during the postmatch recovery period in top-level professional male soccer players' physiological and perceptual markers of recovery status. During the 2022 season (baseline), pneumatic compression was performed as part of the recovery strategy, applied the day after official match play and psychophysiological measurements (pain, sleep, perceived recovery, and creatine kinase [CK] sampling) were performed on the second day postmatch. During the 2023 season, the tDCS protocol was introduced, with its application being performed simultaneously (in conjunction) with pneumatic compression. Recovery sessions following 10 matches in the 2022 season and following 10 matches in the 2023 season were included in the analyses. Compared with 2022 (baseline; pneumatic compression isolated), the players perceived an increased recovery on the second day postmatch when tDCS was used in conjunction with the pneumatic compression (mean = 12%; p = 0.008) and rated improved sleep quality for the nights after applying tDCS combined with pneumatic compression (mean = 7.5%; p = 0.029). On the second day postmatch, a significant reduction was observed in muscle pain/soreness (mean = 64%; p < 0.0001) and the CK concentration decreased when baseline (pneumatic compression isolated) was compared with tDCS + pneumatic compression (mean = 76%; p = 0.001). In summary, combining pneumatic compression with tDCS may enhance the effects of both interventions, leading to greater overall improvements in recovery. Further research is warranted to confirm these findings and explore the underlying mechanisms in more detail.

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.

Simulated Soccer Game Protocols: A Systematic Review on Validated Protocols That Represent the Demands of the Game

ABSTRACT

Brito, P, Costa, J, Figueiredo, P, and Brito, J. Simulated soccer game protocols: A systematic review on validated protocols that represent the demands of the game. J Strength Cond Res 38(1): 192-205, 2024-Several laboratory and field testing protocols have been developed attempting to simulate the activity pattern and physiological demands of soccer. In the present systematic review, we aimed to analyze and discuss the appropriateness, strengths, and limitations of soccer-specific simulated tests. A systematic review of the literature was conducted based on the PRISMA guidelines. Studies conducted in soccer, simulated soccer match tests, and validated simulation protocols performed on-the-field or on a treadmill were considered. No sex restriction was applied, and age >18 years (i.e., adults) was considered. At least 1 outcome measure (e.g., neuromuscular performance, external load, internal load, or psychometric state) of post-simulated-match test or protocol had to be reported. Within the 14 studies included, the average methodological quality of the included articles was 0.61 ± 0.09 (mean ± SD) of 1. Overall, 9 validated protocols were identified. In the protocols, only amateur, university, or semiprofessional soccer players were analyzed. Only one study evaluated female soccer players. None of the studies evaluated the effect on performance over the 2-3 days after the protocol. Accelerations and decelerations, and changes in direction typically present in a game have not been clearly described in any protocol. Future research should address this issue and validate soccer-specific protocols in women.

Individual-Specific Relationship Between External Training and Match Load and Creatine-Kinase Response in Youth National Team Soccer Players

BACKGROUND

Previous studies have examined the relationship between external load and creatine-kinase (CK) response at the team level. This study aimed to build individualized CK prediction models for elite youth national team soccer players.

HYPOTHESIS

The CK response of youth soccer players can be categorized as being sensitive to micromovements (MM), high-velocity (HV) parameters, or the combination of both, measured during training sessions and matches.

STUDY DESIGN

Prospective cohort study.

LEVEL OF EVIDENCE

Level 4.

METHODS

A total of 25 U16-U17 youth national team soccer players were monitored during training sessions and matches using global positioning system (GPS) units. Individual CK values were measured every morning from whole blood. The data set consisted of 57 ± 17 individual datapoints per player. Individual prediction models were used to examine the relationship between external load and consecutive CK changes. Numerous models were built for each player using MM, HV parameters, or the combination of both. The performance of the models was described by the R2 and the root mean square error (RMSE, U/l for CK values).

RESULTS

The MM models were superior for 8 players (R2 = 0.68; RMSE = 113 U/l), followed by HV (8 players; R2 = 0.69; RMSE = 88 U/l) and the combined models (2 players; R2 = 0.64; RMSE = 141 U/l). For the remaining 7 players, the R2 of the models was <0.5. The recovery time between efforts was more important in the HV model.

CONCLUSION

Players could be categorized on sensitivity to MM, HV movements, or the combination of both.

CLINICAL RELEVANCE

These findings can be used to individualize postmatch recovery strategies and to optimize weekly training periodization to maximize match performance.

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.

Relationships between External, Wearable Sensor-Based, and Internal Parameters: A Systematic Review

Micro electro-mechanical systems (MEMS) are used to record training and match play of intermittent team sport athletes. Paired with estimates of internal responses or adaptations to exercise, practitioners gain insight into players' dose-response relationship which facilitates the prescription of the training stimuli to optimize performance, prevent injuries, and to guide rehabilitation processes. A systematic review on the relationship between external, wearable-based, and internal parameters in team sport athletes, compliant with the PRISMA guidelines, was conducted. The literature research was performed from earliest record to 1 September 2020 using the databases PubMed, Web of Science, CINAHL, and SportDISCUS. A total of 66 full-text articles were reviewed encompassing 1541 athletes. About 109 different relationships between variables have been reviewed. The most investigated relationship across sports was found between (session) rating of perceived exertion ((session-)RPE) and PlayerLoad™ (PL) with, predominantly, moderate to strong associations (r = 0.49-0.84). Relationships between internal parameters and highly dynamic, anaerobic movements were heterogenous. Relationships between average heart rate (HR), Edward's and Banister's training impulse (TRIMP) seem to be reflected in parameters of overall activity such as PL and TD for running-intensive team sports. PL may further be suitable to estimate the overall subjective perception. To identify high fine-structured loading-relative to a certain type of sport-more specific measures and devices are needed. Individualization of parameters could be helpful to enhance practicality.

Biomarkers of post-match recovery in semi-professional and professional football (soccer)

High-level football (soccer) players face intense physical demands that result in acute and residual fatigue, impairing their physical performance in subsequent matches. Further, top-class players are frequently exposed to match-congested periods where sufficient recovery times are not achievable. To evaluate training and recovery strategies, the monitoring of players' recovery profiles is crucial. Along with performance and neuro-mechanical impairments, match-induced fatigue causes metabolic disturbances denoted by changes in chemical analytes that can be quantified in different body fluids such as blood, saliva, and urine, thus acting as biomarkers. The monitoring of these molecules might supplement performance, neuromuscular and cognitive measurements to guide coaches and trainers during the recovery period. The present narrative review aims to comprehensively review the scientific literature on biomarkers of post-match recovery in semi-professional and professional football players as well as provide an outlook on the role that metabolomic studies might play in this field of research. Overall, no single gold-standard biomarker of match-induced fatigue exists, and a range of metabolites are available to assess different aspects of post-match recovery. The use of biomarker panels might be suitable to simultaneously monitoring these broad physiological processes, yet further research on fluctuations of different analytes throughout post-match recovery is warranted. Although important efforts have been made to address the high interindividual heterogeneity of available markers, limitations inherent to these markers might compromise the information they provide to guide recovery protocols. Further research on metabolomics might benefit from evaluating the long-term recovery period from a high-level football match to shed light upon new biomarkers of post-match recovery.

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.

Monitoring Postmatch Fatigue During a Competitive Season in Elite Youth Soccer Players

CONTEXT

Countermovement jump (CMJ) and perceived wellness measures are useful for monitoring fatigue. Fatigue indicators should simultaneously show sensitivity to previous load and demonstrate influence on subsequent physical output; however, these factors have not been examined.

OBJECTIVE

To explore the efficacy of CMJ and wellness measures to both detect postmatch fatigue and predict subsequent physical match output in elite youth soccer players.

DESIGN

Cross-sectional study.

PATIENTS OR OTHER PARTICIPANTS

Sixteen soccer players (18 ± 1 years) from 36 English Football League Youth Alliance League fixtures.

MAIN OUTCOME MEASURE(S)

Physical match outputs (total distance, high-speed running, very high-speed running, and accelerations and decelerations [AD]) were recorded using a 10-Hz global positioning system and 200-Hz accelerometer device during competitive match play. The CMJ height and perceived wellness were assessed weekly and daily, respectively, as indirect indicators of fatigue. Four subunits of wellness (perceived soreness, energy, general stress, and sleep) were measured using customized psychometric questionnaires.

RESULTS

Simple linear regression showed that match AD predicted energy (R2 = 0.08, P = .001), stress (R2 = 0.09, P < .001), and total wellness (R2 = 0.06, P = .002) at 2 days postmatch. The CMJ (R2 = 0.05, P = .002), stress (R2 = 0.08, P < .001), sleep (R2 = 0.03, P = .034), and total wellness (R2 = 0.05, P = .006) measures at 5 days prematch predicted AD during the subsequent match.

CONCLUSIONS

The CMJ and wellness measures may be useful for detecting postmatch fatigue. Wellness scores, but not CMJ, at 5 days prematch influenced subsequent match output and therefore may be used to plan and periodize training for the upcoming microcycle.

Individual-based Creatine Kinase Reference Values in Response to Soccer Match-play

The aim of the present study was to determine the creatine kinase reference limits for professional soccer players based on their own normal post-match response. The creatine kinase concentration was analyzed in response to official matches in 25 players throughout a 3-year period. Samples were obtained between 36-43 hours following 70 professional soccer matches and corresponded to 19.1±12.1 [range: 6-49] samples per player. Absolute reference limits were calculated as 2.5^th and 97.5^th percentile of the samples collected. Creatine kinase values were also represented as a percentage change from the individual's season mean and represented by 90^th, 95^th and 97.5^th percentiles. The absolute reference limits for creatine kinase concentration calculated as 97.5^th and 2.5^th percentiles were 1480 U.L^-1 and 115.8 U.L^-1, respectively. The percentage change from the individual's season mean was 97.45±35.92% and players were in the 90^th, 95^th and 97.5^th percentiles when the percentages of these differences were 50.01, 66.7, and 71.34% higher than player's season mean response, respectively. The data allowed us to determine whether the creatine kinase response is typical or if it is indicative of a higher than normal creatine kinase elevation and could be used as a practical guide for detection of muscle overload, following professional soccer match-play.

Effectiveness of the contrast technique as recovery after effort according to professional athletes

Abstract Introduction: Alterations caused in the metabolism of those who practice physical exercise regularly generate health benefits, however, in athletes, these alterations can cause muscle damage, so post-recovery recovery methods are extremely important for their physiological maintenance. Objective: To analyze the effectiveness of the contrast therapy technique with post-exercise recovery according to professional athletes. Methods: A questionnaire was applied that addressed the technical scientific knowledge of professional athletes over 18 years of age, of both sexes, about post-exerciseffort recovery techniques (PERT), personal information, and ethical issues, on an online platform. Descriptive statistical analysis was performed, with values presented in percentages and an association through the Chi-Square test on the knowledge of PERT and other independent variables. Results: In total, 63 athletes, 15 women and 48 men, answered the online questionnaire, 71.4% were between 18 and 30 years old, including swimmers, footballers, and athletics practitioners, and 85.7% had more than three years' experience in the sport and 57.1% competed at an international level. Considering the main PERTs, 92.1% were aware, 58.7% knew more than four, 96.8% frequently used at least one PERT, and 65.1% had used it for more than three years. Knowledge of PERTs is associated with age (p = 0.001), education (p = 0.001), practice time (p = 0.001), hours of daily training (0.001), and competitive level (p = 0.03). With respect to the use of the contrast technique, 36.5% of the respondents had already used it, and 34.9% found it effective. Conclusion: The athletes who used the contrast technique reported a good perception of recovery.

Acute Effects of Training Loads on Muscle Damage Markers and Performance in Semi-elite and Elite Athletes: A Systematic Review and Meta-analysis

BACKGROUND

The relationship between exercise-induced muscle damage (EIMD) indicators and acute training loads (TL) is yet to be reviewed extensively in semi-elite and elite athlete populations.

OBJECTIVES

The objectives of this systematic review and meta-analysis were threefold: (1) to evaluate studies of EIMD following the initial period of the preseason in semi-elite and elite athletes: (2) to examine acute physiological and performance responses across two periods of the season with similar TL; and (3) to examine acute physiological and performance responses to acute changes in TL during the season.

METHODS

The CINAHL, PubMed, Scopus, SPORTDiscus and Web of Science databases were systematically searched for studies that investigated: (1) semi-elite or elite athletes in team or individual sports following a periodised training programme; and (2) measured acute responses to training. Studies were excluded if: (1) conducted in animals; (2) non-English language; or (3) a conference abstract, review or case report. The Kmet Quality Scoring of Quantitative Studies tool was used for study appraisal.

SYNTHESIS METHODS

Data were quantitatively analysed by generating forest plots to report test statistics for statistical significance and inter-trial heterogeneity.

RESULTS

Of the included studies (n = 32), athletes experienced greater creatine kinase (CK) concentrations (Z = 4.99, p < 0.00001, I² = 74%), inflammatory factors and other indirect measures of muscle damage in the initial phase of the preseason period compared to the off-season; there were no changes in CK (Z = 1.43, p = 0.15, I² = 74%) across two time points of similar TL; and there were concurrent increases in CK with increases in TL (Z = 4.26, p < 0.0001, I² = 36%) and vice versa (Z = 4.33, p < 0.0001, I² = 79%).The qualitative analysis identified that the response of inflammatory factors and other indirect measures of muscle damage to changes in load were inconclusive.

LIMITATIONS

This review included varying age, sex, sports and competition levels. The group level meta-analysis failed to identify within-athlete or position-specific differences across time.

CONCLUSION

Blood biomarkers of EIMD may not differ across periods of similar TL, however can be considered a sensitive monitoring tool for assessing responses following acute TL changes in semi-elite and elite athletes.

Internal, external and repeated-sprint demands in small-sided games: A comparison between bouts and age groups in elite youth soccer players

This study investigated the activity profile during small-sided games (SSG) in elite youth soccer players. Internal load (IL) including heart rate (HR) and external load (EL) such as distance covered in different speed-zones (SZ) were collected from forty-eight players of three different teams (U15, U16, U18). The investigation included a total of eighteen 5vs.5 SSGs, each consisting of four 2-minute bouts on a 40x32m pitch during spring season. Total group results (n = 48) showed a reduction in total-distance (p = 0.001; ηp2 = 0.12), high-intensity-running (p = 0.009; ηp2 = 0.09), and low-intensity-running distance (p = 0.028; ηp2 = 0.07) between bouts. Similarly, a reduction in the number of both acceleration-low (p = 0.001; ηp2 = 0.12) and deceleration-high (p = 0.003; ηp2 = 0.11) values was observed. Additionally, time spent in HR-zones 3 and 4 (p≤0.007; ηp2 ≥ 0.10), increased, with a reduction in HR-zone 1 (p = 0.000, ηp2 = 0.25). Age group comparison showed less distance covered in SZ 1 (p≤0.000; ηp2 = 0.56) and greater deceleration-high values (p≤0.038; ηp2 = 0.32) in U15 players compared to other age groups. Further, U15 showed lower values in low-intensity-running compared to U18 (p = 0.038; ηp2 = 0.22). No age-related differences were found for IL and repeated sprint ability (RSA) values. The higher EL in younger age groups should be taken into account when implementing soccer specific SSGs. In addition, HRmean values between 80–85% of HRmax and RSA numbers, which are similar to match-play data, indicate SSGs as an effective training tool to prepare youth soccer athletes for the demands of competition.

Load Measures in Training/Match Monitoring in Soccer: A Systematic Review

In soccer, the assessment of the load imposed by training and a match is recognized as a fundamental task at any competitive level. The objective of this study is to carry out a systematic review on internal and external load monitoring during training and/or a match, identifying the measures used. In addition, we wish to make recommendations that make it possible to standardize the classification and use of the different measures. The systematic review was carried out according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The search was conducted through the electronic database Web of Science, using the keywords "soccer" and "football", each one with the terms "internal load", "external load", and "workload". Of the 1223 studies initially identified, 82 were thoroughly analyzed and are part of this systematic review. Of these, 25 articles only report internal load data, 20 report only external load data, and 37 studies report both internal and external load measures. There is a huge number of load measures, which requires that soccer coaches select and focus their attention on the most useful and specific measures. Standardizing the classification of the different measures is vital in the organization of this task, as well as when it is intended to compare the results obtained in different investigations.

Can Haematological and Hormonal Biomarkers Predict Fitness Parameters in Youth Soccer Players? A Pilot Study

The study aimed to investigate the correlations among immune, haematological, endocrinological markers and fitness parameters, and assess if the physiological parameters could be a predictor of fitness values. Anthropometric, physical evaluations (countermovement jump—CMJ, 10 m sprint, VO₂max, repeated sprint ability—RSA total time and index) and determination of blood (IL-6, IL-10, IL-17A and tumour necrosis factor) and salivary (testosterone and cortisol) samples parameters in 28 young male soccer players (age: 13.0 ± 0.2 years, body mass index (BMI): 19.5 ± 2.2 kg/m²) were analysed. To evaluate the dependence of the variables related to athletic performance, multiple linear regression with backward stepwise elimination was considered. A significant regression equation was found in CMJ (F_(5,16) = 9.86, p < 0.001, R² adjusted = 0.679) and in the RSA index (F_(5,16) = 15.39, p < 0.001, R² adjusted = 0.774) considering only five variables, in a 10 m sprint (F_(4,17) = 20.25, p < 0.001, R² adjusted = 0.786) and in the RSA total time (F_(4,17) = 15.31, p < 0.001, R² adjusted = 0.732) considering only four variables and in VO₂max (F_(9,12) = 32.09, p < 0.001, R² adjusted = 0.930) considering nine variables. Our study suggests the use of regression equations to predict the fitness values of youth soccer players by blood and saliva samples, during different phases of the season, short periods of match congestion or recovery from an injury.

Intra-Individual and Seasonal Variation of Selected Biomarkers for Internal Load Monitoring in U-19 Soccer Players

The aim of this study was to investigate inter-day and -week as well as intra- and inter-individual variation of selected biomarkers in high-performance youth soccer players to assist practitioners interpreting player's internal load to counteract underperformance and unwanted health risks. Eleven male youth soccer players were tested multiple times during two 3-week periods at midpoint (3-wk_mid) and at the end (3-wk_end) of the first half of a German under-19 1. Bundesliga season. The levels of creatine kinase (CK), urea, and C-reactive protein (CRP) were measured during 3-wk_mid and 3-wk_end each Monday, Wednesday, and Friday. In 3-wk_mid the CK median was 14% higher (241 vs. 212 U/L) compared to 3-wk_end (P = 0.26, ES = 0.16). Overall, the medians of CK, urea (P = 0.59, ES = 0.08), and CRP (P = 0.56, ES = 0.10) during 3-wk_mid did not differ to the values of 3-wk_end. Daily coefficient of variations (CVs) ranged from 22 to 71% (CK), 17 to 37% (urea), and 9 to 164% (CRP). Individual medians ranged from 101 to 350 U/L (CK), 23 to 50 mg/dL (urea), and 0.6 to 1.1 mg/L (CRP). High intra-individual variability was demonstrated by large intra-individual CVs (medians: CK 50%, urea 18%, and CRP 45%). Our data show (i) large inter-day and inter-week variability of all biomarkers, depending on the external load and (ii) considerable inter- and intra-individual parameter variations. Creatine kinase concentrations could sensitively reflect soccer-specific loads during the season.

The Use of Small-Sided Games as an Aerobic Fitness Assessment Supplement Within Elite Level Professional Soccer

The purpose of this investigation was to quantify the association between 5 vs. 5 small sided games (SSG) running performance and physiological performance during the Yo-YoIR1 test to ascertain the utility of SSGs as a potential fitness test modality within elite professional soccer players. Twenty-three (n = 23) elite male professional soccer players (mean ± SD age 25.3 ± 3.1 yrs, mass: 76 ± 9 kg, height: 176 ± 9 cm) were assessed. Players completed an intermittent aerobic fitness test (Yo-YoIR1) and a 5 vs. 5 SSGs protocol for the purpose of the study. During all SSGs players wore GPS (Statsports 10-Hz, Viper Pod, Newry, Northern Ireland) and HR monitors (Polar, Oy Kemple, Finland) with these measures related to Yo-YoIR1 running performance. Results revealed SSGs running performance (TD; m) and physiological performance (HR) showed the lowest CV% (< 5%), with high speed movements, accelerations and decelerations highlighting higher CV% during SSGs. Possibly small to possibly very large associations were observed for running performance during 5 vs. 5 SSGs and Yo-YoIR1 performance, with negative associations observed between physiological performance during SSG and YoYoIR1 running performance. To conclude, the current study observed how running performance during a standardised 5 vs. 5 SSG protocol within elite soccer cohorts is associated with the Yo-YoIR1 running performance. Given the low CV%, repeatability and large association of global running performance and internal load measures during a 5 vs. 5 SSG with Yo-YoIR1 performance, this particular soccer specific SSG protocol potentially supplements traditional non-sport specific testing assessments.

Methods to collect and interpret external training load using microtechnology incorporating GPS in professional football: a systematic review

The aim of this article was to systematically review the methods adopted to collect and interpret external training load (ETL) using microtechnology incorporating global positioning system (GPS). The main deficiencies identified concerned the non-collection of match ETL, and the non-consideration of potential confounders (e.g. playing position, fitness level, starting status or session content). Also, complementary training (individual/reconditioning) and pre-match warm-up were rarely quantified. To provide a full picture of the training demands, ETL was commonly complemented by internal training load monitoring with the rating of perceived exertion predominantly adopted instead of heart rate recordings. Continuous data collection and interpretation of ETL data in professional football vary widely between observational studies, possibly reflecting the actual procedures adopted in practical settings. Evidence about continuous ETL monitoring in female players, and female as well as male goalkeepers is lacking.

Internal training load monitoring in professional football: a systematic review of methods using rating of perceived exertion

INTRODUCTION

The rate of perceived exertion (RPE) is widely adopted to quantify internal training load (ITL) in professional football. The aim of this study was to systematically review the use RPE-based methods in professional football.

EVIDENCE ACQUISITION

Observational studies conducted during training routines of professional football players over a minimum of one-week were selected based on the preferred reporting items for systematic reviews and meta-analyses statement.

EVIDENCE SYNTHESIS

Thirty-eight articles met the inclusion criteria (average qualitative score was 6.3 out of 10 [3 to 9]). The main deficiencies identified concerned the poor description of study design (~52% of the studies), and the non-quantification of match load (~44%). Ten studies complemented RPE-based ITL information with time-motion analysis (~26%) and seven studies added HR recordings (~18%). Nine studies collected RPE data after complementary training, separately to field sessions (~3%). Operational questions (e.g. How was your workout? ~71%) were preferred to instructions (e.g. Please rate the intensity of today's session; ~8%). Session-RPE (s-RPE; RPE multiplied by training duration) was more commonly adopted as measure of exercise intensity than isolated RPE (~76 vs. ~8%). RPE-derived variables calculated on weekly values included absolute week-to-week change, acute: chronic workload ratio, monotony and strain and were not frequently used (7 to 15%). Four studies (~11%) divided RPE in two components: respiratory and muscular.

CONCLUSIONS

There is a lack of consensus for the use of RPE in professional football and "good practices" are warranted. This review might help practitioners regarding procedures to adopt in RPE data collection and interpretation.

A comparison of the isometric force fatigue-recovery profile in two posterior chain lower limb tests following simulated soccer competition

Aim

To evaluate the reliability of isometric peak force (IPF) in a novel “long-length” 90°Hip:20°Knee (90:20) strength test and to compare the simulated soccer match induced fatigue-recovery profile of IPF in this test with that of an isometric 90°Hip:90°Knee (90:90) position test.

Methods

Twenty semi-professional soccer players volunteered for the study of which 14 participated in the first part of the study which assessed 90:20 reliability (age = 21.3 ± 2.5 years, height = 1.79 ± 0.07 m, body mass = 73.2 ± 8.8 kg), while 17 completed the second part of the study evaluating fatigue-recovery (age 21.2±2.4 yrs., height = 180 ± 0.09 m, body mass 73.8 ± 8.9 kg). We evaluated the inter-session reliability of IPF in two 90:20 test protocols (hands on the wall (HW); and hands on chest (HC)) both performed on two occasions, 7 days apart. We then assessed 90:20 (HC) and 90:90 IPF immediately before (PRE) and after (POST) after a simulated soccer match protocol (BEAST90mod) and 48 (+48 h) and 72 hours (+72 h) later.

Results

Part one: the 90:20 showed moderate to high overall reliability (CV’s of 7.3% to 11.0%) across test positions and limbs. CV’s were lower in the HW than HC in the dominant (7.3% vs 11.0%) but the opposite happened in the non-dominant limb where CV’s were higher in the HW than HC (9.7% vs 7.3%). Based on these results, the HC position was used in part two of the study. Part two: 90:20 and 90:90 IPF was significantly lower POST compared to PRE BEAST90mod across all testing positions (p<0.001). IPF was significantly lower at +48 h compared to PRE in the 90:20 in both limbs (Dominant: p<0.01,Non-dominant: p≤0.05), but not in the 90:90. At +72 h, IPF was not significantly different from PRE in either test.

Conclusions

Simple to implement posterior IPF tests can help to define recovery from competition and training load in football and, potentially, in other multiple sprint athletes. Testing posterior chain IPF in a more knee extended 90:20 position may provide greater sensitivity to fatigue at 48 h post simulated competition than testing in the 90:90 position, but also may require greater degree of familiarization due to more functional testing position.

Relationship of Pre-season Training Load With In-Season Biochemical Markers, Injuries and Performance in Professional Soccer Players

INTRODUCTION

There is controversy in the literature in regards of the link between training load and injury rate. Thus, the aims of this non-interventional study were to evaluate relationships between pre-season training load with biochemical markers, injury incidence and performance during the first month of the competitive period in professional soccer players.

MATERIALS AND METHODS

Healthy professional soccer players were enrolled in this study over two pre-season periods. Data sets were available from 26 players during the first season (2014-2015) and 24 players during the second season (2015-2016) who completed two pre-season periods (6 weeks each). External training load was assessed from all athletes during training using Global Positioning System (GPS). Internal training load was monitored after each training session using rate of perceived exertion (RPE). Before and after each pre-season, blood samples were taken to determine plasma lactate dehydrogenase (LDH), creatine kinase (CK) and C-reactive protein (CRP). Injury incidence and overall performance (ranking of the team after the first five official games of the championship) were recorded for both seasons separately.

RESULTS

There was no statistically significant difference in mean RPE values of the two-preparation periods (2737 ± 452 and 2629 ± 786 AU, p = 0.492). The correlational analysis did not reveal significant associations between internal and external training load (RPE and GPS data) and biological markers. There was a significant positive correlation between RPE and LDH during the 2015/2016 season (r = 0.974, p = 0.001). In addition, a significant negative correlation was found between total distance >20 km/h and CRP during the 2015-2016 season (r = -0.863, p = 0.027). The injury rates for the two seasons were 1.76 and 1.06 per 1000 h exposure for the 2014-2015 and 2015-2016 seasons, respectively (p = 0.127).

CONCLUSION

Our study showed that pre-season training load is not associated with overall team performance. This association is most likely multifactorial and other factors (e.g., technical and tactical level of the team, opponents, environment) may play an important role for the collective team performance. Our findings may help coaches to better prepare their athletes during pre-season.

Effects of Compression Tights on Recovery Parameters after Exercise Induced Muscle Damage: A Randomized Controlled Crossover Study

Introduction

Recent meta-analyses on compression garments have reported faster recovery of muscle function particularly after intense eccentric power or resistance exercise. However, due to the complex interaction between cohorts included, exercises involved and compression applied, recovery length and modalities, and outcome parameters selected, only limited practical recommendations can be drawn from these studies. Thus, our aim was to determine the effect of compression tights on recovery from high mechanical and metabolic stress monitored over a longer recovery period.

Material and Methods

Using a crossover design, 19 resistance-trained 4^th/5^th Division German handball players (31.3±7.7 years; 24.1±3.8 kg/m²) were randomly assigned at the start of the project to the compression tight (recovery-pro-tights, cep, Bayreuth, Germany) or the control group. Immediately after a combined lower extremity resistance training and electromyostimulation, participants had to wear compression tights. Compression was applied initially for 24 h and then 12 h intermitted by 12 h of nonuse for a total of 96 h. Primary study endpoint was maximum isokinetic hip/leg-extensor strength (MIES) as determined by a leg-press. Secondary endpoint was lower extremity power as assessed by a counter movement jump. Follow-up assessments were conducted 24, 48, 72, and 96 h postexercise. Outcomes were analyzed using a linear mixed effect model with spherical symmetric within-condition correlation.

Results

All 19 participants underwent their allocated treatment and passed through the project strictly according to the study protocol. MIES demonstrated significantly (p=0.003) lower overall reductions (155 N) after wearing compression tights. In parallel, lower extremity power significantly (p<0.001) varies between both conditions with lower reductions in favor of the compression condition. Of importance, full recovery for lower extremity muscle strength or power was still not reached 96 h postexercise.

Conclusion

Based on our results we recommend athletes wear compression tights for faster recovery, particularly after intense exercise with a pronounced eccentric aspect.

Perceived training load and jumping responses following nine weeks of a competitive period in young female basketball players

The aims of this study were to describe the session rating of perceived exertion (sRPE), total quality recovery (TQR), and variations in countermovement jump (CMJ) height throughout nine weeks of a competitive period in young female basketball players. In total, 10 young female basketball players (17.2 ± 0.4 years; 71.8 ± 15.0 kg; 177.2 ± 9.5 cm) participated in this study. The sRPE and TQR were assessed in each training session, whereas the CMJ height was assessed prior to the first weekly training session. The magnitude-based inferences method was used to compare the sRPE, TQR, and CMJ height across the nine weeks of training. The training loads accumulated in weeks 1, 2, and 3 were likely to almost certainly be higher than in the following weeks (ES varying from 0.67 to 2.55). The CMJ height in week 1 was very likely to be lower than in weeks 2, 5, 7, and 8 (ES varying from 0.24 to 0.34), while the CMJ height of the 9th week was likely to almost certainly be higher than all previous weeks of training (ES varying from 0.70 to 1.10). Accordingly, it was observed that when higher training loads were accumulated, both CMJ and TQR presented lower values than those presented during periods with lower internal training loads. These results highlight the importance of using a comprehensive and multivariate approach to effectively monitor the physical performance of young athletes.