Biceps femoris long head muscle and aponeurosis geometry in males with and without a history of hamstring strain injury.

OBJECTIVES: Hamstring strain injuries (HSIs) commonly affect the proximal biceps femoris long head (BFlh) musculotendinous junction. Biomechanical modeling suggests narrow proximal BFlh aponeuroses and large muscle-to-aponeurosis width ratios increase localized tissue strains and presumably risk of HSI. This study aimed to determine if BFlh muscle and proximal aponeurosis geometry differed between limbs with and without a history of HSI. METHODS: Twenty-six recreationally active males with (n = 13) and without (n = 13) a history of unilateral HSI in the last 24 months underwent magnetic resonance imaging of both thighs. BFlh muscle and proximal aponeurosis cross-sectional areas, length, volume, and interface area between muscle and aponeurosis were extracted. Previously injured limbs were compared to uninjured contralateral and control limbs for discrete variables and ratios, and along the relative length of tissues using statistical parametric mapping. RESULTS: Previously injured limbs displayed significantly smaller muscle-to-aponeurosis volume ratios (p = 0.029, Wilcoxon effect size (ES) = 0.43) and larger proximal BFlh aponeurosis volumes (p = 0.019, ES = 0.46) than control limbs with no history of HSI. No significant differences were found between previously injured and uninjured contralateral limbs for any outcome measure (p = 0.216-1.000, ES = 0.01-0.36). CONCLUSIONS: Aponeurosis geometry differed between limbs with and without a history of HSI. The significantly larger BFlh proximal aponeuroses and smaller muscle-to-aponeurosis volume ratios in previously injured limbs could alter the strain experienced in muscle adjacent to the musculotendinous junction during active lengthening. Future research is required to determine if geometric differences influence the risk of re-injury and whether they can be altered via targeted training.

Load Centralization Does Not Affect the Kinetic and Kinematic Output of Countermovement Jumps.

ABSTRACT: Tredrea, MSJ, Middleton, KJ, Bourne, MN, Carey, DL, Scanlan, AT, and Dascombe, BJ. Load centralization does not affect the kinetic and kinematic output of countermovement jumps. J Strength Cond Res 36(4): 1084-1089, 2022-This study aimed to compare the kinetics, kinematics, and performance of countermovement jumps (CMJs) when completed with 2 different loading conditions (centralized or peripheral) across increasing loads. Seventeen subjects (12 men and 5 women) randomly completed 2 series of CMJs with increasing loads separated by a 30-minute rest period between conditions. Subjects were loaded with either a weighted vest (centralized) or straight barbell (peripheral). A randomized, counterbalanced crossover design was used with incremental loads of 10, 20, 30, 40, and 50% of body mass added to the vest or barbell. Measures of peak force, acceleration, velocity, and power were calculated across each subphase of the CMJs. No significant differences were observed in kinetic or kinematic variables between loading conditions. Within each condition there were significant reductions (p < 0.05) in peak concentric velocity and acceleration, as well as significant increases (p < 0.05) in peak force when the external load increased. Furthermore, braking and propulsive phase duration significantly increased (p < 0.05) and jump height significantly decreased (p < 0.05) as the external load increased. Countermovement jump performance was similar in both central and peripheral loading, whereas increasing load significantly affected jump height, force, velocity, and acceleration variables irrespective of load position. The training stimulus from an external load placed centrally or peripherally is similar regardless of where it is positioned; however, from a practical perspective, a weighted vest may provide a more mobile and safer alternative than a barbell.

A prospective study of risk factors for hamstring injury in Australian football league players.

This study aimed to explore the association between hamstring strength, age and lower limb soft tissue injury history and subsequent hamstring injury among Australian Football League (AFL) players. This prospective cohort study recruited 125 players from three professional AFL teams. Eccentric knee flexor strength was assessed while performing the Nordic hamstring exercise in pre-season, and injury data were collected retrospectively (hamstring, groin, calf, quadriceps and knee), and prospectively (hamstring injuries) for one AFL playing season. Fourteen players (11%) sustained a hamstring injury in the subsequent playing season. Nordic strength was not significantly associated with future hamstring injury (Odds Ratio (OR) 1.9, p = 0.36), whereas player age greater than 25 years (OR = 2.9, p < 0.05), report of a hamstring injury within the previous year (OR = 3.7, p = 0.01), or greater than 1-year (OR = 3.6, p = 0.01), a previous groin (OR = 8.6, p < 0.01) or calf injury (OR = 4.6, p = 0.01) were factors significantly associated with subsequent hamstring injury. Based on these findings, increasing age and previous hamstring, groin and calf injury are all associated with an elevated risk of subsequent hamstring injury in AFL players.

Hamstring and gluteal activation during high-speed overground running: Impact of prior strain injury.

This study examined the spatial patterns of hamstring and gluteal muscle activation during high-speed overground running in limbs with and without aprior hamstring strain injury. Ten active males with arecent (<18 month) unilateral biceps femoris long head (BFLH) strain injury underwent functional magnetic resonance imaging before and immediately after arepeat-sprint running protocol. Transverse relaxation (T2) time, an index of muscle activation, of the BFLH and short head (BFSH), semitendinosus (ST), semimembranosus (SM), gluteus maximus (GMAX) and medius (GMED) was assessed pre-post exercise. No significant between-limb differences in running-induced mean T2 changes were observed (p = 0.949), however, decision tree induction revealed that previously injured limbs were characterised by highly variable intramuscular activation of the ST (SD5.3). T2 times increased more for GMAX than all other muscles (all p< 0.001, d= 0.5-2.5). Further, T2 changes were greater for ST than BFSH, SM, GMED, and BFLH (all p≤ 0.001, d= 0.5-2.9); and were greater for BFLH than BFSH, SM, and GMED (all p< 0.001, d= 1.2-1.6). Athletes display heterogenous patterns of posterior thigh activation when sprinting (GMAX>ST>BFLH>GMED>SM>BFSH) and may exhibit altered intramuscular hamstring activation after returning to sport from BFLH strain injury.

Recalibrating the risk of hamstring strain injury (HSI): A 2020 systematic review and meta-analysis of risk factors for index and recurrent hamstring strain injury in sport.

OBJECTIVE: To systematically review risk factors for hamstring strain injury (HSI). DESIGN: Systematic review update. DATA SOURCES: Database searches: (1) inception to 2011 (original), and (2) 2011 to December 2018 (update). Citation tracking, manual reference and ahead of press searches. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Studies presenting prospective data evaluating factors associated with the risk of index and/or recurrent HSI. METHOD: Search result screening and risk of bias assessment. A best evidence synthesis for each factor and meta-analysis, where possible, to determine the association with risk of HSI. RESULTS: The 78 studies captured 8,319 total HSIs, including 967 recurrences, in 71,324 athletes. Older age (standardised mean difference=1.6, p=0.002), any history of HSI (risk ratio (RR)=2.7, p<0.001), a recent HSI (RR=4.8, p<0.001), previous anterior cruciate ligament (ACL) injury (RR=1.7, p=0.002) and previous calf strain injury (RR=1.5, p<0.001) were significant risk factors for HSI. From the best evidence synthesis, factors relating to sports performance and match play, running and hamstring strength were most consistently associated with HSI risk. The risk of recurrent HSI is best evaluated using clinical data and not the MRI characteristics of the index injury. SUMMARY/CONCLUSION: Older age and a history of HSI are the strongest risk factors for HSI. Future research may be directed towards exploring the interaction of risk factors and how these relationships fluctuate over time given the occurrence of index and recurrent HSI in sport is multifactorial.

Hamstring muscle activation and morphology are significantly altered 1-6 years after anterior cruciate ligament reconstruction with semitendinosus graft.

PURPOSE: Harvest of the semitendinosus (ST) tendon for anterior cruciate ligament reconstruction (ACLR) causes persistent hypotrophy of this muscle even after a return to sport, although it is unclear if hamstring activation patterns are altered during eccentric exercise. It was hypothesised that in comparison with contralateral control limbs, limbs with previous ACLR involving ST grafts would display (i) deficits in ST activation during maximal eccentric exercise; (ii) smaller ST muscle volumes and anatomical cross-sectional areas (ACSAs); and (iii) lower eccentric knee flexor strength. METHODS: Fourteen athletes who had successfully returned to sport after unilateral ACLR involving ST tendon graft were recruited. Median time since surgery was 49 months (range 12-78 months). Participants underwent functional magnetic resonance imaging (MRI) of their thighs before and after the Nordic hamstring exercise (NHE) and percentage change in transverse (T2) relaxation time was used as an index of hamstring activation. Muscle volumes and ACSAs were determined from MRI and distal ST tendons were evaluated via ultrasound. Eccentric knee flexor strength was determined during the NHE. RESULTS: Exercise-induced T2 change was lower for ST muscles in surgical than control limbs (95% CI - 3.8 to - 16.0%). Both ST muscle volume (95% CI - 57.1 to - 104.7 cm3) and ACSA (95% CI - 1.9 to - 5.0 cm2) were markedly lower in surgical limbs. Semimembranosus (95% CI 5.5-14.0 cm3) and biceps femoris short head (95% CI 0.6-11.0 cm3) volumes were slightly higher in surgical limbs. No between-limb difference in eccentric knee flexor strength was observed (95% CI 33 N to - 74 N). CONCLUSION: ST activation is significantly lower in surgical than control limbs during eccentric knee flexor exercise 1-6 years after ACLR with ST graft. Lower levels of ST activation may partially explain this muscle's persistent hypotrophy post ACLR and have implications for the design of more effective rehabilitation programs. LEVEL OF EVIDENCE: IV.

Razor hamstring curl and Nordic hamstring exercise architectural adaptations: Impact of exercise selection and intensity.

OBJECTIVES: To investigate knee flexor strength and biceps femoris long head (BFlh) architectural adaptations following two different Nordic hamstring exercise (NHE) interventions and one razor hamstring curl (RHC) intervention. METHODS: Thirty recreationally active males performed a total of 128 reps of NHEbodyweight (n = 10), NHEweighted (n = 10), or RHCweighted training (n = 10) across 6 weeks. Following the intervention, participants avoided any eccentric training for 4 weeks (detraining period). Strength results during the NHE and RHC were recorded pre- and post-intervention, as well as following detraining. Architectural characteristics of the BFlh were assessed weekly throughout the intervention and detraining periods. RESULTS: For the NHEweighted group, NHE strength increased (+81N, P = 0.044, d = 0.90) and BFlh fascicles lengthened (+1.57 cm, P < 0.001, d = 1.41) after 6 weeks of training. After 1 week of detraining, BFlh fascicle lengths shortened, with the largest reductions seen in the NHEweighted group (-0.96 cm, P = 0.021, d = -0.90). Comparatively, BFlh fascicle length and NHE strength responses were moderate in the NHEbodyweight group and negligible in the RHCweighted group. The greatest RHC strength changes (+82N, P = 0.038, d = 1.15) were seen in the RHCweighted group. CONCLUSIONS: NHEweighted interventions induce large BFlh fascicle lengthening responses and these adaptations decay after just 1 week of detraining. NHEbodyweight training has a moderate impact on BFlh architecture while the RHCweighted group has the least. Weighted NHE and RHC training promoted exercise-specific increases in strength. These findings suggest that exercise selection and intensity should be considered when prescribing exercises aiming to increase eccentric strength and BFlh fascicle length.

Isokinetic strength assessment offers limited predictive validity for detecting risk of future hamstring strain in sport: a systematic review and meta-analysis.

OBJECTIVE: To examine the value of isokinetic strength assessment for predicting risk of hamstring strain injury, and to direct future research into hamstring strain injuries. DESIGN: Systematic review. DATA SOURCES: Database searches for Medline, CINAHL, Embase, AMED, AUSPORT, SPORTDiscus, PEDro and Cochrane Library from inception to April 2017. Manual reference checks, ahead-of-press and citation tracking. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Prospective studies evaluating isokinetic hamstrings, quadriceps and hip extensor strength testing as a risk factor for occurrence of hamstring muscle strain. METHODS: Independent search result screening. Risk of bias assessment by independent reviewers using Quality in Prognosis Studies tool. Best evidence synthesis and meta-analyses of standardised mean difference (SMD). RESULTS: Twelve studies were included, capturing 508 hamstring strain injuries in 2912 athletes. Isokinetic knee flexor, knee extensor and hip extensor outputs were examined at angular velocities ranging 30-300°/s, concentric or eccentric, and relative (Nm/kg) or absolute (Nm) measures. Strength ratios ranged between 30°/s and 300°/s. Meta-analyses revealed a small, significant predictive effect for absolute (SMD=-0.16, P=0.04, 95% CI -0.31 to -0.01) and relative (SMD=-0.17, P=0.03, 95% CI -0.33 to -0.014) eccentric knee flexor strength (60°/s). No other testing speed or strength ratio showed statistical association. Best evidence synthesis found over half of all variables had moderate or strong evidence for no association with future hamstring injury. SUMMARY/CONCLUSION: Despite an isolated finding for eccentric knee flexor strength at slow speeds, the role and application of isokinetic assessment for predicting hamstring strain risk should be reconsidered, particularly given costs and specialised training required.

Impact of exercise selection on hamstring muscle activation.

OBJECTIVE: To determine which strength training exercises selectively activate the biceps femoris long head (BFLongHead) muscle. METHODS: We recruited 24 recreationally active men for this two-part observational study. Part 1: We explored the amplitudes and the ratios of lateral (BF) to medial hamstring (MH) normalised electromyography (nEMG) during the concentric and eccentric phases of 10 common strength training exercises. Part 2: We used functional MRI (fMRI) to determine the spatial patterns of hamstring activation during two exercises which (1) most selectively and (2) least selectively activated the BF in part 1. RESULTS: Eccentrically, the largest BF/MH nEMG ratio occurred in the 45° hip-extension exercise; the lowest was in the Nordic hamstring (Nordic) and bent-knee bridge exercises. Concentrically, the highest BF/MH nEMG ratio occurred during the lunge and 45° hip extension; the lowest was during the leg curl and bent-knee bridge. fMRI revealed a greater BF(LongHead) to semitendinosus activation ratio in the 45° hip extension than the Nordic (p<0.001). The T2 increase after hip extension for BFLongHead, semitendinosus and semimembranosus muscles was greater than that for BFShortHead (p<0.001). During the Nordic, the T2 increase was greater for the semitendinosus than for the other hamstring muscles (p≤0.002). SUMMARY: We highlight the heterogeneity of hamstring activation patterns in different tasks. Hip-extension exercise selectively activates the long hamstrings, and the Nordic exercise preferentially recruits the semitendinosus. These findings have implications for strategies to prevent hamstring injury as well as potentially for clinicians targeting specific hamstring components for treatment (mechanotherapy).

Impact of the Nordic hamstring and hip extension exercises on hamstring architecture and morphology: implications for injury prevention.

BACKGROUND: The architectural and morphological adaptations of the hamstrings in response to training with different exercises have not been explored. PURPOSE: To evaluate changes in biceps femoris long head (BFLH) fascicle length and hamstring muscle size following 10-weeks of Nordic hamstring exercise (NHE) or hip extension (HE) training. METHODS: 30 recreationally active male athletes (age, 22.0±3.6 years; height, 180.4±7 cm; weight, 80.8±11.1 kg) were allocated to 1 of 3 groups: (1) HE training (n=10), NHE training (n=10), or no training (control, CON) (n=10). BFLH fascicle length was assessed before, during (Week 5) and after the intervention with a two-dimensional ultrasound. Hamstring muscle size was determined before and after training via MRI. RESULTS: Compared with baseline, BFLH fascicles were lengthened in the NHE and HE groups at mid-training (d=1.12-1.39, p<0.001) and post-training (d=1.77-2.17, p<0.001) and these changes did not differ significantly between exercises (d=0.49-0.80, p=0.279-0.976). BFLH volume increased more for the HE than the NHE (d=1.03, p=0.037) and CON (d=2.24, p<0.001) groups. Compared with the CON group, both exercises induced significant increases in semitendinosus volume (d=2.16-2.50, ≤0.002) and these increases were not significantly different (d=0.69, p=0.239). CONCLUSION: NHE and HE training both stimulate significant increases in BFLH fascicle length; however, HE training may be more effective for promoting hypertrophy in the BFLH.

Short biceps femoris fascicles and eccentric knee flexor weakness increase the risk of hamstring injury in elite football (soccer): a prospective cohort study.

BACKGROUND/AIM: To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femoris long head (BFlh) fascicle length on the risk of future hamstring strain injury (HSI). METHODS: Elite soccer players (n=152) from eight different teams participated. Eccentric knee flexor strength during the Nordic hamstring exercise and BFlh fascicle length were assessed at the beginning of preseason. The occurrences of HSIs following this were recorded by the team medical staff. Relative risk (RR) was determined for univariate data, and logistic regression was employed for multivariate data. RESULTS: Twenty seven new HSIs were reported. Eccentric knee flexor strength below 337 N (RR=4.4; 95% CI 1.1 to 17.5) and possessing BFlh fascicles shorter than 10.56 cm (RR=4.1; 95% CI 1.9 to 8.7) significantly increased the risk of a HSI. Multivariate logistic regression revealed significant effects when combinations of age, history of HSI, eccentric knee flexor strength and BFlh fascicle length were explored. From these analyses the likelihood of a future HSI in older athletes or those with a HSI history was reduced if high levels of eccentric knee flexor strength and longer BFlh fascicles were present. CONCLUSIONS: The presence of short BFlh fascicles and low levels of eccentric knee flexor strength in elite soccer players increases the risk of future HSI. The greater risk of a future HSI in older players or those with a previous HSI is reduced when they have longer BFlh fascicles and high levels of eccentric strength.

Concurrent validity and test-retest reliability of VALD ForceDecks' strength, balance, and movement assessment tests.

OBJECTIVES: To evaluate the concurrent validity and test-retest reliability of common movement, strength, and balance tests using portable uniaxial dual force plates. DESIGN: Repeated measures cross-sectional study. METHODS: Sixteen healthy individuals participated in two testing sessions, where they performed 12 different movement, strength, and balance tests. Vertical ground reaction force and centre of pressure data were collected using the VALD ForceDecks simultaneously with ground-embedded laboratory force plates. Concurrent validity was assessed using root mean square error for raw time-series data and Bland-Altman plots for discrete metrics. Test-retest reliability was assessed using intraclass correlation coefficients and minimal detectable changes. RESULTS: ForceDecks recorded vertical ground reaction forces and center of pressure with high accuracy compared to laboratory force plates. The mean bias between systems was negligible (<2 N or 0.1 mm), with small limits of agreement (<5 N or 1 mm). Overall, 530/674 (79%) showed good or excellent validity (<10% difference) and 611/773 (79%) had good or excellent reliability (intraclass correlation coefficient >0.75). ForceDecks reliability was similar to laboratory force plates (<0.07 intraclass correlation coefficient median difference for all metrics). CONCLUSIONS: Portable uniaxial force plates record highly accurate vertical ground reaction forces and center of pressure during a range of movement, strength, and balance tests. The VALD ForcDecks are a valid and reliable alternative to laboratory force plates when strict standardized testing and data analysis procedures are followed. Users should be aware of the validity and reliability characteristics of the tests and metrics they choose.

Vertical Jump Testing after Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-analysis.

INTRODUCTION: Recently, there has been a call for vertical jump testing via force-plate analysis to be included in the assessment of individuals after anterior cruciate ligament reconstruction (ACLR) and as part of return-to-play criteria. However, a synthesis of current literature is needed to help guide clinicians on what tests to perform, which force-plate metrics to assess, and how these may change over the time course of rehabilitation. METHODS: Four online databases were searched from inception to July 2022. The Downs and Black checklist was used to assess study quality. Multilevel meta-analyses and meta-regressions were undertaken in conjunction with a best evidence synthesis. RESULTS: Forty-two articles were included, capturing 2375 participants with a history of ACLR. Reconstructed limbs displayed 1) lower peak eccentric forces, concentric forces, landing forces, and lower eccentric and concentric impulses (standardized means difference [SMD] = -1.84 to -0.46) than uninjured contralateral limbs during bilateral countermovement jumps (CMJ) and drop vertical jumps (DVJ); 2) lower jump heights and reactive strength indices (RSI), and longer contact times than uninjured contralateral limbs during unilateral CMJ and DVJ (SMD = -0.86 to 0.26); and 3) lower jump heights, RSI, and longer contact times during bilateral and unilateral CMJ, and unilateral DVJ, than uninjured controls (SMD = -1.19 to 1.08). Meta-regression revealed that time postsurgery was a significant moderator ( P < 0.05) for 1) bilateral CMJ height, peak concentric force, and peak landing force; 2) between-limb differences in unilateral CMJ height; and 3) differences in unilateral DVJ height, RSI, and contact time between reconstructed limbs and healthy controls with no history of injury. CONCLUSIONS: Individuals with a history of ACLR display chronic deficits in vertical jumping performance during a range of bilateral and unilateral tasks, which may have implications for return-to-play criteria and the design of interventions targeted at restoring long-term deficits in explosive lower limb strength after ACLR.

Inclusion of a skeletal model partly improves the reliability of lower limb joint angles derived from a markerless depth camera.

A single depth camera provides a fast and easy approach to performing biomechanical assessments in a clinical setting; however, there are currently no established methods to reliably determine joint angles from these devices. The primary aim of this study was to compare joint angles as well as the between-day reliability of direct kinematics to model-constrained inverse kinematics recorded using a single markerless depth camera during a range of clinical and athletic movement assessments.A secondary aim was to determine the minimum number of trials required to maximize reliability. Eighteen healthy participants attended two testing sessions one week apart. Tasks included treadmill walking, treadmill running, single-leg squats, single-leg countermovement jumps, bilateral countermovement jumps, and drop vertical jumps. Keypoint data were processed using direct kinematics as well as in OpenSim using a full-body musculoskeletal model and inverse kinematics. Kinematic methods were compared using statistical parametric mapping and between-day reliability was calculated using intraclass correlation coefficients, mean absolute error, and minimal detectable change. Keypoint-derived inverse kinematics resulted in significantly smaller hip flexion (range = -9 to -2°), hip abduction (range = -3 to -2°), knee flexion (range = -5° to -2°), and greater dorsiflexion angles (range = 6-15°) than direct kinematics. Both markerless kinematic methods had high between-day reliability (inverse kinematics ICC 95 %CI = 0.83-0.90; direct kinematics ICC 95 %CI = 0.80-0.93). For certain tasks and joints, keypoint-derived inverse kinematics resulted in greater reliability (up to 0.47 ICC) and smaller minimal detectable changes (up to 13°) than direct kinematics. Performing 2-4 trials was sufficient to maximize reliability for most tasks. A single markerless depth camera can reliably measure lower limb joint angles, and skeletal model-constrained inverse kinematics improves lower limb joint angle reliability for certain tasks and joints.

Hamstring and knee injuries are associated with isometric hip and trunk muscle strength in elite Australian Rules and Rugby League players.

OBJECTIVES: This study investigated relationships between isometric trunk and hip extensor strength, lumbar muscle morphology, and the risk of hamstring and knee ligament injuries in Australian Football League and National Rugby League players. DESIGN: Prospective cohort study. METHODS: Trunk and hip extensor strength, multifidus and quadratus lumborum cross-sectional area were measured during the 2020 pre-season. Logistic regressions and decision trees were employed to explore associations between maximum strength, strength endurance, multifidus and quadratus lumborum cross-sectional area, age, previous injuries, and hamstring and knee ligament injury risk. RESULTS: Greater strength endurance [odds ratio = 0.42 (0.23-0.74), p = 0.004] and maximum strength [odds ratio = 0.55 (0.31-0.94), p = 0.039] reduced hamstring injury risk. Increased risk of knee ligament injuries was associated with larger multifidus [odds ratio = 1.66 (1.14-2.45), p = 0.008] and higher multifidus to quadratus lumborum ratio (odds ratio = 1.57 (1.13-2.23), p = 0.008]. Decision tree models indicated that low strength endurance (< 99 Nm) characterised hamstring strains, while high (≥ 1.33) multifidus to quadratus lumborum ratio mitigated risk. Knee ligament injuries were associated with larger (≥ 8.49 cm2) multifidus, greater (≥ 1.25) multifidus to quadratus lumborum ratio, and lower maximum strength (< 9.24 N/kg). CONCLUSIONS: Players with lower trunk and hip extensor maximum strength and strength endurance had increased risk of hamstring injuries, while knee ligament injury risk was elevated with larger multifidus cross-sectional area, higher multifidus to quadratus lumborum ratio, and lower maximum trunk and hip extensor strength.

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

PURPOSE: The aim of this systematic review was to (1) determine the muscle fiber-type composition (or muscle fiber typology [MFT]) of team-sport athletes and (2) examine associations between MFT and the physical characteristics and performance tasks in team-sport athletes. METHODS: Searches were conducted across numerous databases-PubMed, SPORTDiscus, MEDLINE, and Google Scholar-using consistent search terms. Studies were included if they examined the MFT of team-sport athletes. Included studies underwent critical appraisal using the McMasters University critical appraisal tool for quantitative research. RESULTS: A total of 10 studies were included in the present review, wherein the MFT of athletes was measured from 5 different team sports (soccer, rugby union, rugby league, handball, and volleyball). There was large variability in the MFT of team-sport athletes both within (up to 27.5%) and between sports (24.0% relative difference). Male football players with a higher proportion of type II fibers had faster 10- and 30-m sprint times, achieved a greater total distance sprinting (distance at >6.67 m·s-1), and a greater peak 1-minute sprint distance. CONCLUSIONS: MFT varies considerably between athletes both within and between different team sports. The results from some studies suggest that variation in MFT is associated with high-intensity running performance in a football match, as well as 10- and 30-m sprint times. Further experimental studies should focus on how determination of the MFT of team-sport athletes could be utilized to influence talent identification, team selection, and the individualization of training.

Injury Prevention Programmes Fail to Change Most Lower Limb Kinematics and Kinetics in Female Team Field and Court Sports: A Systematic Review and Meta-Analysis of Randomised Controlled Trials.

BACKGROUND: One mechanism by which exercise interventions may be effective in reducing anterior cruciate ligament (ACL) injury risk is through changes in lower limb biomechanics. Understanding how training programmes affect lower-limb kinematics and kinetics may help refine injury prevention programmes. OBJECTIVE: The aim of this systematic review and meta-analysis was to assess the effect of injury prevention programmes on kinematics and kinetics during tasks related to ACL injury in female team field and court sports. DATA SOURCES: Five databases were searched in October 2022. ELIGIBILITY CRITERIA: Randomised controlled trials assessing the effect of injury prevention programmes compared with usual training/no training on lower limb kinematics and kinetics in female team field and court sports were eligible for review. RESULTS: Sixteen studies were included. A total of 976 female athletes were included. Most of the studies included interventions with multiple components (12/16). Commonly used components were plyometrics (12/16), strength (8/16), and balance/stability (7/16). Thirteen studies had routine training or sham interventions as the control group and three studies had no training. Very low certainty evidence suggests that injury prevention programmes increase knee flexion angles (mean difference = 3.1° [95% confidence interval 0.8-5.5]); however, very low to low certainty evidence suggests no effect on hip flexion angles/moments, knee flexion moments, hip adduction angles/moments, knee adduction angles/moments, hip internal rotation angles/moments, ankle dorsiflexion angles, and ground reaction forces, compared with usual training/no training. CONCLUSION: Injury prevention programmes may be effective in increasing knee flexion angles during dynamic landing and cutting tasks but may have no effect on other lower limb biomechanical variables. As such, the benefits of injury prevention programmes may be mediated by factors other than altered biomechanics and/or may happen through other biomechanical measures not included in this review.

Hamstring strain injury prevention: current beliefs and practices of practitioners working in Major League Baseball.

CONTEXT: Hamstring strain injuries (HSIs) are the most frequently sustained injury in Major League Baseball (MLB). However, the beliefs and practices of MLB practitioners regarding HSI risk factors and prevention strategies in baseball athletes, have not been documented. OBJECTIVE: To document the current beliefs and practices of MLB practitioners in relation to HSI prevention. DESIGN: cross-sectional study. SETTING: Major League Baseball via an online survey. PARTICIPANTS: Athletic trainers, physical therapists and strength and conditioning coaches employed in MLB during the 2021 season. DATA COLLECTION AND ANALYSIS: An online survey was conducted with participants completing the survey once. Questions pertained to risk factor identification, the use and perceived effectiveness of preventative strategies, and barriers to implementation. Descriptive statistics were calculated for each question. RESULTS: 91 responses were received featuring respondents from 28 of 30 MLB organizations. The perceived most important intrinsic risk factor for first-time HSI was tolerance to high-speed running and previous HSI for recurrent injury. The perceived most important extrinsic risk factor for both first-time and recurrent HSI was internal communication between staff.The perceived most effective prevention strategies were managing overall workload, exposure to high-speed running, and periodization. The most used prevention strategies were core/lumbopelvic strengthening, resistance training and workload management.Approximately half (53%) of respondents reported barriers to effective implementation of HSI prevention strategies, including player and coach buy-in, compliance, training time constraints, and in-season scheduling/reduced recovery time. CONCLUSIONS: This was the first survey to investigate MLB practitioner beliefs and practices regarding HSI prevention. Responses from practitioners regarding their beliefs about risk factors and appropriate prevention strategies were varied, and discrepancies existed between the perceived most effective strategies and those most frequently employed.

Gluteal Muscle Forces during Hip-Focused Injury Prevention and Rehabilitation Exercises.

PURPOSE: This study aimed to compare and rank gluteal muscle forces in eight hip-focused exercises performed with and without external resistance and describe the underlying fiber lengths, velocities, and muscle activations. METHODS: Motion capture, ground reaction forces, and electromyography (EMG) were used as input to an EMG-informed neuromusculoskeletal model to estimate gluteus maximus, medius, and minimus muscle forces. Participants were 14 female footballers (18-32 yr old) with at least 3 months of lower limb strength training experience. Each participant performed eight hip-focused exercises (single-leg squat, split squat, single-leg Romanian deadlift [RDL], single-leg hip thrust, banded side step, hip hike, side plank, and side-lying leg raise) with and without 12 repetition maximum (RM) resistance. For each muscle, exercises were ranked by peak muscle force, and k-means clustering separated exercises into four tiers. RESULTS: The tier 1 exercises for gluteus maximus were loaded split squat (95% confidence interval [CI] = 495-688 N), loaded single-leg RDL (95% CI = 500-655 N), and loaded single-leg hip thrust (95% CI = 505-640 N). The tier 1 exercises for gluteus medius were body weight side plank (95% CI = 338-483 N), loaded single-leg squat (95% CI = 278-422 N), and loaded single-leg RDL (95% CI = 283-405 N). The tier 1 exercises for gluteus minimus were loaded single-leg RDL (95% CI = 267-389 N) and body weight side plank (95% CI = 272-382 N). Peak gluteal muscle forces increased by 28-150 N when exercises were performed with 12RM external resistance compared with body weight only. Peak muscle force coincided with maximum fiber length for most exercises. CONCLUSIONS: Gluteal muscle forces were exercise specific, and peak muscle forces increased by varying amounts when adding a 12RM external resistance. These findings may inform exercise selection by facilitating the targeting of individual gluteal muscles and optimization of mechanical loads to match performance, injury prevention, or rehabilitation training goals.