Metabolic limitations of performance and fatigue in football

A Review of the Validity and Reliability of Accelerometer-Based Metrics From Upper Back-Mounted GNSS Player Tracking Systems for Athlete Training Load Monitoring

ABSTRACT

Dawson, L, Beato, M, Devereux, G, and McErlain-Naylor, SA. A review of the validity and reliability of accelerometer-based metrics from upper back-mounted GNSS player tracking systems for athlete training load monitoring. J Strength Cond Res 38(8): e459-e474, 2024-Athlete load monitoring using upper back-mounted global navigation satellite system (GNSS) player tracking is common within many team sports. However, accelerometer-based load monitoring may provide information that cannot be achieved with GNSS alone. This review focuses on the accelerometer-based metrics quantifying the accumulation of accelerations as an estimation of athlete training load, appraising the validity and reliability of accelerometer use in upper back-mounted GNSS player tracking systems, the accelerometer-based metrics, and their potential for application within athlete monitoring. Reliability of GNSS-housed accelerometers and accelerometer-based metrics are dependent on the equipment model, signal processing methods, and the activity being monitored. Furthermore, GNSS unit placement on the upper back may be suboptimal for accelerometer-based estimation of mechanical load. Because there are currently no feasible gold standard comparisons for field-based whole-body biomechanical load, the validity of accelerometer-based load metrics has largely been considered in relation to other measures of training load and exercise intensity. In terms of convergent validity, accelerometer-based metrics (e.g., PlayerLoad, Dynamic Stress Load, Body Load) have correlated, albeit with varying magnitudes and certainty, with measures of internal physiological load, exercise intensity, total distance, collisions and impacts, fatigue, and injury risk and incidence. Currently, comparisons of these metrics should not be made between athletes because of mass or technique differences or between manufacturers because of processing variations. Notable areas for further study include the associations between accelerometer-based metrics and other parts of biomechanical load-adaptation pathways of interest, such as internal biomechanical loads or methods of manipulating these metrics through effective training design.

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.

Perceptions of Football Analysts Goal-Scoring Opportunity Predictions: A Qualitative Case Study

This study aimed to understand the way tactical football analysts perceive the general match analysis issues and to analyze their tactical interpretation of the predictive models of conceded goal-scoring opportunities. Nine tactical analysts responded to the semi-structured interviews that included a general section on the match analysis and a specific one on the results of a study on goal-scoring opportunities conceded by a Spanish La Liga team. Following their transcription, the interviews were codified into categories by the two researchers using Atlas Ti® software. Subsequently, frequency count and co-occurrence analysis were performed based on the encodings. The content analysis reflected that analysts play a crucial role in the analysis of their own team and that of the opponent, the essential skills to exercise as a tactical analyst being "understanding of the game" and "clear observation methodology." Based on the case study of the conceded goal-scoring opportunities, the major causes and/or solutions attributed by analysts in some of the predictive models were the adaptability of the "style of play" itself according to the "opponent" and "pressure after losing."

Effects of Different Recovery Times on Internal and External Load During Small-Sided Games in Soccer

BACKGROUND

The ability to maintain a high intensity of exercise over several repetitions depends on recovery from previous exercises. This study aimed to identify the effects of different recovery times on internal and external load during small-sided soccer games.

HYPOTHESIS

An increase in recovery time will increase the external training load and decrease the internal exercise load, which will result in a greater physical impact of the exercise.

STUDY DESIGN

Cross-sectional study.

LEVEL OF EVIDENCE

Level 2.

METHODS

Twenty male semiprofessional soccer players participated in the present study. They performed the same exercise (5-a-side game format) continuously (1 × 18 minutes) and repeatedly/fractionated (3 × 6 minutes) with different recovery times (30 seconds, 1 minute, 1.5 minutes, and 2 minutes). Their internal load (ie, average heart rate (HR) and maximum HR) and external load (ie, total distance, maximum speed, and ratio meters) were measured using an HR band and an inertial device equipped with a global positioning system, respectively.

RESULTS

The manipulation of recovery times induced differences in the internal and external load. For the same total duration, the external and internal load indicators exhibited higher values during the fractionated method, particularly with short recovery periods.

CONCLUSION

The application of small-sided soccer games with different recovery times induced varying responses in training load. To maintain high physical performance and high training load, the fractional method with short recovery periods (ie, 30 seconds) should be used. In contrast, to carefully manage players' efforts and decrease response to training load, continuous or fractional methods with longer recovery periods (ie, 1-2 minutes) should be used.

CLINICAL RELEVANCE

The proper prescription of recovery time between exercises facilitates enhanced training efficiency and optimized performance.

The Relationship between Body Mass Index, Body Fat Percentage, and Dietary Intake with Muscle Fatigue in Adolescent Football Players

It is important for football players to maintain muscle strength through the entire match. The aim of this study was to investigate body mass index (BMI), body fat percentage (BF%), dietary intake (energy, carbohydrate, and protein) and its relationship with muscle fatigue among adolescent football players. This was a cross-sectional study involving 26 football players aged 15-17 y. BMI was determined using WHO Anhtro Plus, BF% was analyzed using Bioelectrical Impedance Analysis (BIA) and categorized using bodyfat curves for children, and dietary intake was assessed using 3×24 h dietary recall. Running-Based Anaerobic Sprint Test (RAST) was conducted twice and averaged to identify muscle fatigue. Pearson correlation and multiple-regression analysis were performed to determine the relationship between variables. The results showed that overall participants had healthy weight (17.61±1.82 kg/m2), good diet pattern (energy 99.08±14.34%, carbohydrate 92.88±9.54% and protein 95.96±23.41%), but low body fat (6.76±2.12%). In pearson test, negative correlations were found in muscle fatigue and BMI (r=-0.393, p=0.047), as well as BF% (r=-0.458, p=0.019), but positive between muscle fatigue and energy intake (r=0.538, p=0.005). Furthermore, multiple-regression analysis only confirmed statistically significant relationship between energy intake and muscle fatigue (p=0.028). We conclude that the higher BMI and BF% may lead to greater muscle fatigue, while higher energy intake has significant improvement to reduce muscle fatigue. Hence, it is essential for football players to consume adequate energy, and consider to maintain BMI and BF% at optimal range.

Indirect Assessment of Skeletal Muscle Glycogen Content in Professional Soccer Players before and after a Match through a Non-Invasive Ultrasound Technology

Skeletal muscle glycogen (SMG) stores in highly glycolytic activities regulate muscle contraction by controlling calcium release and uptake from sarcoplasmic reticulum, which could affect muscle contraction. Historically, the assessment of SMG was performed through invasive and non-practical muscle biopsies. In this study we have utilized a novel methodology to assess SMG through a non-invasive high-frequency ultrasound. Nine MLS professional soccer players (180.4 ± 5.9 cm; 72.4 ± 9.3 kg; 10.4% ± 0.7% body fat) participated. All followed the nutritional protocol 24 h before the official match as well as performing the same practice program the entire week leading to the match. The SMG decreased from 80 ± 8.6 to 63.9 ± 10.2; p = 0.005 on MuscleSound^® score (0–100) representing a 20% ± 10.4% decrease in muscle glycogen after match. Inter-individual differences in both starting glycogen content (65–90) and in percentage decrease in glycogen after the match (between 6.2% and 44.5%). Some players may not start the match with adequate SMG while others’ SMG decreased significantly throughout the game. Adequate pre-match SMG should be achieved during half-time and game-play in order to mitigate the decrease in glycogen. Further and more ample studies are needed before the application of this technology.

Halftime Rewarm-up With Intermittent Exercise Improves the Subsequent Exercise Performance of Soccer Referees

Yanaoka, T, Yamagami, J, Kidokoro, T, Kashiwabara, K, and Miyashita, M. Halftime rewarm-up with intermittent exercise improves the subsequent exercise performance of soccer referees. J Strength Cond Res 32(1): 211-216, 2018-This study investigated the effect of halftime rewarm-up (RW) with intermittent exercise on the subsequent exercise performance of soccer referees, determined by the Yo-Yo Intermittent Recovery Test level 1 (Yo-Yo IR1). Using a randomized cross-over design, 10 male referees were required to complete 2 trials. The trials consisted of the Loughborough Intermittent Shuttle Test, halftime, and Yo-Yo IR1 periods. During halftime, participants either rested on a chair (Control) or performed a halftime RW exercise for 15 minutes. The halftime RW protocol comprised 2.15 minutes of seated rest, followed by 2.15 minutes of running at 70% of the maximum heart rate (HRmax)-this cycle of recovery and running was repeated for a total of 13 minutes. The halftime RW protocol started at 1 minute after the commencement of the halftime period and concluded 1 minute before its end. The Yo-Yo IR1 performance, blood glucose, free fatty acids (FFAs), triglycerides (TGs), creatine kinase (CK), and lactate concentrations, the rating of perceived exertion, mean HR, and HRmax were analyzed. The Yo-Yo IR1 performance was higher in the halftime RW trial than in the control trial (3,095 ± 326 vs. 2,904 ± 421 m, P ≤ 0.05). The mean HR and HRmax, blood glucose, FFA, TG, CK, and lactate concentrations did not differ between the trials. The rating of perceived exertion during the halftime RW, but not after the Yo-Yo IR1 period, was higher than that in the control trial. In conclusion, this study showed that halftime RW with intermittent exercise improves the subsequent exercise performance.

Temporal Changes in Technical and Physical Performances During a Small-Sided Game in Elite Youth Soccer Players

Background

There have been claims that small-sided games (SSG) may generate an appropriate environment to develop youth players’ technical performance associated to game-related problem solving. However, the temporal change in technical performance parameters of youth players during SSG is still unknown.

Objectives

The aim of this study was to examine temporal changes in technical and physical performances during a small-sided game (SSG) in elite soccer players.

Methods

Sixty elite youth players (age 14.8 ± 0.2 yr; stature 177 ± 5 cm; body mass 66.2 ± 4.7 kg) completed a 5 v 5 SSG using two repetitions of 8 minutes interspersed by 3 minutes of passive recovery. To evaluate temporal changes in performance, the data were analysed across 4 minutes quarters. Physical performance parameters included the total distance covered (TDC), the frequency of sprints (>18 km•h^-1), accelerations and decelerations (> 2.0 m•s^-2 and - 2.0 m•s^-2), metabolic power (W•kg^-1), training impulse (TRIMP), TDC: TRIMP, number of impacts, and body load. Technical performance parameters included goal attempts, total number of tackles, tackles and interceptions, total number of passes, and passes effectiveness.

Results

All physical performance parameters decreased from the first to the last quarter with notable declines in TDC, metabolic power and the frequency of sprints, accelerations and decelerations (P < 0.05; moderate to very large ES: 1.08 - 3.30). However, technical performance parameters did not vary across quarters (P > 0.05; trivial ES for 1st v 4th quarters: 0.15 - 0.33).

Conclusions

The data demonstrate that technical performance is maintained despite substantial declines in physical performance during a SSG in elite youth players. This finding may have implications for designing SSG’s for elite youth players to ensure physical, technical and tactical capabilities are optimized. Modifications in player number, pitch dimensions, rules, coach encouragement, for instance, should be included taking into account the main aim of a given session and then focused on overloading physical or technical elements.

Heat stress and physical capacity: a case study of semi-professional footballers

BACKGROUND

The aim of this study was to determine heat stress effect on physical capacity of semi-professional footballers in Iran by means of oxygen consumption measurement, heart rate monitoring and WBGT assessment environmental conditions.

METHODS

This study compared two different thermal environmental conditions related to sub-maximal exercise and its effect on human physical capacity. Thirty two male footballers (age 25.9 ± 1.4 year; height 176 ± 2.9 cm and weight 71 ± 9.8 kg) were investigated under four workloads (50,100,150 & 200 W) in two different thermal conditions in the morning (WBGT=21 °C) and afternoon (WBGT=33 °C) in summer. Each test cycle lasted for 10 minutes with a 10 min interval for recovery and rest between every workload. In the end of each stage, the heart rate, blood pressure, skin temperature and oral temperature were measured and recorded. Expired air was collected and its volume was measured using standard Douglas bags. The WBGT index was also used to monitor the stressful heat condition.

RESULTS

Heart rate and VO2 consumption findings for different workload showed a significant difference between morning and afternoon (P<0.001). HR and VO2 consumption in both morning and afternoon courses showed a liner relation (r=0.88, r=0.9 respectively).

CONCLUSION

With increasing work load beside heat stress, heart rate and oxygen consumption increased. It is recommended that with Ta>35 °C or WBGT>28 °C, physical activates and performing exercises should be avoided in order to reduce the risk of heat stress-related conditions in athletes.

The effect of carbohydrate ingestion on performance during a simulated soccer match

Aim: This study investigated how performance was affected after soccer players, in a postprandial state, ingested a 7% carbohydrate (CHO) solution compared to a placebo (0% CHO) during a simulated soccer match. Methods: Using a double-blind placebo-controlled design, 22 trained male league soccer players (age: 24 ± 7 years, wt: 73.4 ± 12.0 kg, VO₂max: 51.8 ± 4.3 mL O₂/kg/min) completed two trials, separated by 7 days, during which they ingested, in random order, 700 mL of either a 7% CHO or placebo drink during a simulated soccer match. Ratings of perceived exertion (RPE), agility, timed and run to fatigue were measured during the trials. Results: Change in agility times was not altered by CHO vs. placebo ingestion (0.57 ± 1.48 vs. 0.66 ± 1.00, p = 0.81). Timed runs to fatigue were 381 ± 267 s vs. 294 ± 159 s for the CHO and placebo drinks, respectively (p = 0.11). Body mass modified the relationship between time to fatigue and drink ingestion (p = 0.02 for drink × body mass), such that lower body mass was associated with increased time to fatigue when the players ingested CHO, but not placebo. RPE values for the final stage of the simulated soccer match were 8.5 ± 1.7 and 8.6 ± 1.5 for the CHO and placebo drinks respectively (p = 0.87). Conclusions: The group data showed that the 7% CHO solution (49 g CHO) did not significantly improve performance during a simulated soccer match in league soccer players who had normal pre-match nutrition. However, when adjusting for body mass, increasing CHO intake was associated with improved time to fatigue during the simulated soccer match.