The Relevance of Muscle Fiber Type to Physical Characteristics and Performance in Team-Sport Athletes

Sprinters' and Marathon Runners' Performances Are Better Explained by Muscle Fibers' Percentage Cross-Sectional Area than Any Other Parameter of Muscle Fiber Composition

The present study aimed to investigate the correlation between muscle fiber type variables and sprinting, jumping, strength, power and endurance performances in sprinters and marathon runners. Furthermore, the study explored which muscle fiber type variable influences athletes' performance the most and which variable discriminates sprinters from marathon runners. Body composition, vastus lateralis muscle fiber composition, sprinting, jumping, strength, maximum isometric force, rate of force development and endurance performance were assessed in well-trained sprinters (n = 15; age: 24.7 ± 4.1 years; body mass: 82.7 ± 8.8 kg; body fat: 11.3 ± 4.2%) and marathon runners (n = 15; age: 26.1 ± 3.2 years; body mass: 69.7 ± 4.3 kg; body fat: 9.5 ± 3.3%). Significant correlations were observed between muscle fiber composition variables and performances (r = -0.848 to 0.902; p < 0.05), with percentage cross-sectional areas (%CSAs) showing the strongest associations. Regression analyses confirmed %CSAs as the strongest predictors of performance (R2: 0.796-0.978; p < 0.001; B coefficients: -0.293-0.985), while discriminant analysis accurately differentiated sprinters from marathon runners (100%, p < 0.001) by only using athletes' muscle fibers' %CSAs. In conclusion, muscle fibers' %CSAs may be the most critical variables for explaining and distinguishing sprinters' and marathon runners' performances.

Influence of time-of-day on neuromuscular performance in team sport athletes: a systematic review and meta-analysis

Introduction

Although circadian rhythms have been shown to influence some neuromuscular performance tasks, the time-of-day effect on team sports performance athletes remains equivocal. This study aimed to examine the existing evidence concerning diurnal variations in neuromuscular performance in professional and semi-professional team sports athletes using a meta-analytic approach.

Methods

A literature search was conducted through three different databases: PubMed, SportDiscus and Web of Science. Article selection was made based on the following inclusion criteria: team sports athletes, professional or semi-professional athletes, neuromuscular performance, testing protocols and time-of-day testing times. Neuromuscular performance parameters such vertical jump capacity (i.e., squat and countermovement jump), agility and isometric strength were included in the analysis. Testing protocols that specifically assessed these parameters across morning (AM) and late afternoon/evening (PM) periods were considered were extracted from the selected studies.

Results

Ten studies met the inclusion criteria for qualitative synthesis and five for quantitative synthesis. Meta-analysis indicated lower countermovement jump in the AM compared to with PM (mean difference, -1.44; 95% CI -2.80 to -0.08; p = 0.04) and higher agility performance (mean difference 0.42; 95% CI 0.09-0.74; p = 0.01) in PM comparing with AM. No differences were reported in isometric strength and squat jump performance (p > 0.05).

Conclusion

Neuromuscular performance is higher in the late afternoon or early evening compared to morning schedules in team sport athletes. Hence, time-of-day variations need to be considered when evaluating neuromuscular performance in professional and semi-professional team sports athletes.

Impact of a 20-Week Resistance Training Program on the Force-Velocity Profile in Novice Lifters Using Isokinetic Two-Point Testing

Objectives: This study aimed to assess the impact of a 20-week resistance training program on force-velocity (F-V) parameters using an isokinetic two-point method and comparing one-repetition maximum (1-RM) methods in novice lifters. Methods: Previously untrained individuals completed a supervised, three-session weekly resistance training program involving concentric, eccentric, and isometric phases, repeated every 2 to 4 weeks. Isokinetic dynamometry measured the strength of elbow flexors/extensors at 60°/s and 150°/s, and knee flexors/extensors at 60°/s and 240°/s at Baseline, 3 months, and 5 months. F-V parameters, including maximal theoretical force (F0) and the F-V slope, were calculated. Participants also performed 1-RM tests for the upper and lower limbs. Repeated measures ANOVA with effect size (η2 > 0.14 as large) was used to analyze changes in F-V parameters and repeated measures correlation was used to test their association with 1-RM outcomes. Results: Eighteen male participants (22.0 ± 3.4 years) were analyzed. F0 significantly increased for all muscle groups (η2 = 0.423 to 0.883) except elbow flexors. F-V slope significantly decreased (steeper) for knee extensors and flexors (η2 = 0.348 to 0.695). Knee extensors showed greater F0 gains and steeper F-V slopes than flexors (η2 = 0.398 to 0.686). F0 gains were associated with 1-RM changes (r = 0.38 to 0.83), while F-V slope changes correlated only with lower limb 1-RM (r = -0.37 to -0.68). Conclusions: The 20-week resistance training program significantly increased F0 and shifted the F-V profile towards a more "force-oriented" state in knee muscles. These changes correlated with improved 1-RM performance. Future studies should include longer follow-ups and control groups.

Estimating Muscle Fiber-Type Composition in Elite Athletes: A Survey on Current Practices and Perceived Merit

PURPOSE

To gather information on practices and perceptions of high-performance experts regarding their athletes' muscle fiber-type composition (MFTC) and its estimation.

METHODS

A questionnaire on the noninvasive versus invasive estimation of MFTC was completed by 446 experts including coaches and sport-science/sports-medicine staff. Moreover, the perceived importance of MFTC for training and performance optimization was assessed. Differences between sport types (individual and team sports) were analyzed using chi-square tests.

RESULTS

Forty percent of the experts implemented MFTC assessment in pursuit of performance optimization, while 50% did not know their athletes' MFTC but expressed a desire to implement it if they would be able to assess MFTC. Ten percent did not perceive value in MFTC assessment. Only 18% of experts believed that their athletes would undergo a muscle biopsy, leading to the adoption of alternative noninvasive techniques. Experts primarily relied on their experience to estimate MFTC (65%), with experts working in individual sports using their experience more frequently than those working in team sports (68% vs 51%; P = .009). Jump tests emerged as the second-most commonly employed method for estimating MFTC (56%). When only considering experts who are currently using MFTC, 87% use MFTC to individualize training volume and 84% to individualize training intensity.

CONCLUSIONS

Experts value MFTC assessment primarily to individualize training but mainly rely on noninvasive methods to estimate MFTC. Some of these methods lack scientific validity, suggesting a continuing need for education and further research in this area.

The Relationship Between the Anaerobic Speed Reserve and Acute Responses to High-Intensity Interval Training in Female Soccer Players

ABSTRACT

Aspin, GL, Graham, M, Franklin, J, Hicks, KM, and Taylor, JM. The relationship between the anaerobic speed reserve and acute responses to high-intensity interval training in female soccer players. J Strength Cond Res 38(11): 1911-1916, 2024-The anaerobic speed reserve (ASR) is a popular method of profiling soccer players, often used to individualize training prescription. This study explored the reliability of ASR profiling, and the relationship between the ASR and acute physiological responses to high-intensity interval training (HIIT). Acute physiological responses to different HIIT types were also compared. Thirteen subelite female soccer players aged 20.2 ± 4.6 years completed 6 exercise sessions. In sessions 1-2, players completed a 40-m sprint to assess maximal sprint speed (MSS) and 1600-m time-trial to estimate maximal aerobic speed (MAS), which were used to calculate ASR and assess test-retest reliability. In sessions 3-6, players completed 4 HIIT sessions (repeated-sprint training, sprint interval training, long intervals, and short intervals HIIT). Intensities for long and short intervals HIIT were individualized according to MAS. Ratings of perceived exertion (RPE), heart rate (HR), and postsession blood lactates were recorded throughout. Relationships between the ASR and acute responses to HIIT, and between HIIT session comparisons in outcome measures were assessed. Anaerobic speed reserve (coefficient of variation ± 95% confidence limits; 3.1 ± 1.5%), MAS (1.8 ± 1.3%), and MSS (0.8 ± 0.6%) indicated acceptable reliability. Moderate correlations between ASR and RPE ( r = 0.33), postsession blood lactate ( r = 0.34), and HR ( r = 0.37) were observed during long intervals HIIT. A strong correlation was observed between ASR and RPE during SIT ( r = 0.50). Sprint interval training elicited higher RPE's and postsession blood lactate's than other HIIT sessions. Anaerobic speed reserve has good reliability and may influence acute physiological responses to HIIT in female soccer players.

Anthropometric and mechanical factors determining sprint in young soccer players: a brief report

Sprint performance is a critical factor in soccer. While previous studies have extensively explored the biomechanical, physiological, and metabolic determinants of sprinting, the impact of anthropometric variables in team sports contexts, especially soccer, remains underexplored. This study aims to investigate the influence of anthropometric and mechanical variables on sprint performance in young soccer players. Fifty-eight young soccer players were evaluated in anthropometry and a 30-meter (m) sprint using radar technology. Split times in 5, 15, and 30 m were determined, in addition to the assessment of the force-velocity profile proposed by Morin and Samozino. Results: Key anthropometric variables associated with improved sprint performance included lower-limb muscle mass at distances 5 and 15 m (R 2 = 0.08 and R 2 = 0.09, respectively, both with small effects). Additionally, body composition, particularly a lower % body fat, was crucial across all sprint distances (ES: large). Among the mechanical variables, max power (R 2 = 0.997, ES: large) and maximum velocity (R 2 = 0.553, ES: large) are the mechanical variables that were most strongly associated with sprint performance over distances greater than 30 m. Soccer coaches, athletic trainers, and strength and conditioning specialists working with young athletes can apply the findings of this study to their training programming.

Predicting Sprint Performance From the Vertical and Horizontal Jumps in National Football League Combine Athletes

ABSTRACT

Agar-Newman, DJ, MacRae, F, Tsai, M-C, and Klimstra, M. Predicting sprint performance from the vertical and horizontal jumps in National Football League Combine athletes. J Strength Cond Res 38(8): 1433-1439, 2024-Identifying fast athletes is an important part of the National Football League (NFL) Combine. However, not all athletes partake in the 36.58-m sprint, and relying on this single test may miss potentially fast athletes. Therefore, the purpose of this study was to determine whether sprinting times can be predicted using simple anthropometric and jumping measures. Data from the NFL Combine between the years 1999-2020 inclusive were used (n = 4,149). Subjects had a mean (±SD) height = 1.87 ± 0.07 m and body mass = 111.96 ± 20.78 kg. The cross-validation technique was used, partitioning the data into a training set (n = 2,071) to develop regression models to predict time over the 9.14-, 9.14- to 18.29-, 18.29- to 36.58-m, and 36.58-m segments using vertical jump, broad jump, height, and mass as the independent variables. The models were then evaluated against a test set (n = 2,070) for agreement. Statistically significant (p < 0.01) models were determined for 9.14-m time (adjusted R2 = 0.76, SEE = 0.05 seconds), 9.14- to 18.29-m time (adjusted R2 = 0.74, SEE = 0.04 seconds), 18.29- to 36.59-m time (adjusted R2 = 0.79, SEE = 0.07 seconds), and 36.58-m time (adjusted R2 = 0.84, SEE = 0.12 seconds). When evaluated against the test set, the models showed biases of -0.05, -0.04, -0.02, and -0.02 seconds and root-mean-square error of 0.07, 0.05, 0.07, and 0.12 seconds for the 9.14-, 9.14- to 18.29-, 18.29- to 36.58-m, and 36.58-m segments, respectively. However, 5-6% of the predictions lay outside of the limits of agreement. This study provides 4 formulae that can be used to predict sprint performance when the 36.58-m sprint test is not performed, and practitioners can use these equations to determine training areas of opportunity when working with athletes preparing for the NFL Combine.

Effects of β-Alanine Supplementation on Subjects Performing High-Intensity Functional Training

BACKGROUND

β-alanine, a non-essential amino acid found in the diet and produced through nucleotide catabolism, is significant for muscle performance due to its role in carnosine synthesis. This study aims to assess the impact of a 4-week β-alanine supplementation on neuromuscular fatigue in individuals engaging in High-Intensity Functional Training (HIFT) and its subsequent effect on sports performance, distinguishing between central fatigue from the CNS and peripheral fatigue from the muscular system.

MATERIALS AND METHODS

This study (a randomized controlled trial) comprised a total of 27 subjects, who were divided into two groups. Group A (the control group) was administered sucrose powder, while Group B (the experimental group) was given β-alanine powder. The subjects were randomly assigned to either the experimental or control groups. This study lasted four weeks, during which both groups participated in high-intensity interval training (HIFT) on the first day to induce fatigue and work close to their VO2 max.

RESULTS

Statistically significant changes were in the sports performance variables, specifically vertical jump and jumping power (p = 0.027). These changes were observed only in the group that had been supplemented with β-alanine. Nevertheless, no alterations were observed in any other variables, including fatigue, metabolic intensity of exercise, or perceived intensity (p > 0.05).

CONCLUSIONS

A four-week β-alanine intake program demonstrated an improvement in the capacity of subjects, as evidenced by enhanced vertical jump and power performance. Nevertheless, it does result in discernible alterations in performance.

Effects of exercise on muscle fiber conversion, muscle development and meat quality of Sunit sheep

This study aimed to investigate the effects of exercise on muscle fiber conversion, muscle development and meat quality in the biceps femoris (BF) muscle of Sunit sheep. Twelve Sunit sheep with similar body weight were divided into two groups: control group (C group) and exercise group (E group), E group lambs underwent 6 km of exercise training per day for 90 d. The findings revealed that compared with the C group, exercise training enhanced the expression of MyHC IIa mRNA, decreased the number ratio of type IIB muscle fibers and the expression of MyHC IIb mRNA (P < 0.05). Furthermore, the E group lamb displayed higher creatine kinase (CK) activity, and lactic acid levels (P < 0.05), while glycogen content and lactic dehydrogenase (LDH) activity showed opposite trends (P < 0.05). Exercise significantly up-regulated the mRNA expression of AMP-activated protein kinase α1 (AMPKα1), sirtuin1 (SIRT1), peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α), cytochrome c oxidase IV (COX IV), protein kinase B (Akt), mammalian target of rapamycin (mTOR) and p70 Ribosomal S6 Kinase 1 (p70s6k1) (P < 0.05), suggesting exercise promoted muscle fiber conversion by mediating AMPK/PGC-1α pathway, and improved skeletal muscle development via Akt/mTOR pathway. Besides, backfat thickness and pH45min value in the E group decreased significantly, while the pH24, a*, and shear force value increased significantly (P < 0.05). To conclude, this study suggested that exercise training can be used to alter muscle fiber characteristics and muscle development in lamb production.

Hamstrings mechanical properties profiling in football players of different competitive levels and positions after a repeated sprint protocol

Purpose: This study compares the average speed, knee flexor peak torque and shear modulus of the hamstrings after a repeated sprint task, in football players of different competitive levels and playing positions. Methods: Fifty-four football field players without hamstring strain injury history participated, 15 being categorized as professional (2nd league) and 39 as semi-professional (17 in 3rd and 22 in 4th league). Muscle shear modulus was assessed using ultrasound-based shear wave elastography at rest and at 20% of maximal voluntary isometric effort before and immediately after the repeated sprint protocol. Results: No significant differences were seen in average sprint speed between competitive levels (p = 0.07; η2p = 0.28) and positions (p = 0.052; η2p = 0.29). Moreover, the sprint fatigue index showed no significant differences between competitive levels (p = 0.14; η2p = 0.08) and playing positions (p = 0.89; η2p = 0.05). No significant differences were observed in hamstring shear modulus changes between competitive levels (p = 0.94; η2p = 0.03) and positions (p = 0.92; η2p = 0.03). Peak torque changes also showed non-significant association with competitive levels (p = 0.46; η2p = 0.03) and positions (p = 0.60; η2p = 0.02). Conclusion: The results of this study suggest that the average sprint speed performance parameter and mechanical parameters are not able to distinguish football players of different competitive levels and positions.

Energy cost differences between marathon runners and soccer players: Constant versus shuttle running

Purpose: In the last decades, the energy cost assessment provided new insight on shuttle or constant running as training modalities. No study, though, quantified the benefit of constant/shuttle running in soccer-players and runners. Therefore, the aim of this study was to clarify if marathon runners and soccer players present specific energy cost values related to their training experience performing constant and shuttle running. Methods: To this aim, eight runners (age 34 ± 7.30y; training experience 5.70 ± 0.84y) and eight soccer-players (age 18.38 ± 0.52y; training experience 5.75 ± 1.84y) were assessed randomly for 6' on shuttle-running or constant-running with 3 days of recovery in-between. For each condition, the blood lactate (BL) and the energy cost of constant (C_r) and shuttle running (C_Sh) was determined. To assess differences for metabolic demand in terms of C_r, C_Sh and BL over the two running conditions on the two groups a MANOVA was used. Results: V·O_2max were 67.9 ± 4.5 and 56.8 ± 4.3 ml·min^-1 kg^-1 (p = 0.0002) for marathon runners and soccer players, respectively. On constant running, the runners had a lower C_r compared to soccer players (3.86 ± 0.16 J kg^-1m^-1 vs. 4.19 ± 0.26 J kg^-1 m^-1; F = 9.759, respectively; p = 0.007). On shuttle running, runners had a higher C_Sh compared to soccer players (8.66 ± 0.60 J kg^-1 m^-1 vs. 7.86 ± 0.51 J kg^-1 m^-1; F = 8.282, respectively; with p = 0.012). BL on constant running was lower in runners compared to soccer players (1.06 ± 0.07 mmol L^-1 vs. 1.56 ± 0.42 mmol L^-1, respectively; with p = 0.005). Conversely, BL on shuttle running was higher in runners compared to soccer players 7.99 ± 1.49 mmol L^-1 vs. 6.04 ± 1.69 mmol L^-1, respectively; with p = 0.028). Conclusion: The energy cost optimization on constant or shuttle running is strictly related to the sport practiced.