BFlh Fascicle Length Research Articles

A retrospective comparison of the biceps femoris long head muscle structure in athletes with and without hamstring strain injury history.

Hamstring strain injuries (HSI) and re-injuries are endemic in high-speed running sports. The biceps femoris long head (BFlh) is the most frequently injured muscle among the hamstrings. Structural parameters of the hamstring muscle are stated to be susceptible to strain injuries at this location. This retrospective study targeted comparing the BFlh's structural parameters between previously injured and uninjured athletes. Nineteen male athletes with previous BFlh strain injury history and nineteen athletes without former lower extremity injury history were included in this study. Fascicle length, mid-muscle belly and distal musculotendinous (MTJ) passive stiffnesses of the biceps femoris long head (BFlh) were examined via b-mode panoramic ultrasound scanning and ultrasound-based shear-wave elastography. Parameter comparisons of both legs within and between athletes with and without injury history were performed. Comparison of the BFlh fascicle length between the injured leg of the injured group and the legs of the controls revealed a trend to shorter fascicle lengths in the injured leg (p = 0.067, d = -0.62). However, the mid-muscle belly passive stiffness of the BFlh was significantly higher in the injured legs (p = 0.009, d = 0.7) compared with the controls. Additionally, the distal MTJ stiffness was much higher in the previously injured legs compared with controls (p < 0.001, d = 1.6). Outcomes support the importance of BFlh properties related to stiffness, and fascicle length for injury susceptibility in athletes. Future prospective studies should determine whether the higher stiffness in the injured athletes is a cause or consequence of the HSI. Physical therapy and rehabilitation programmes after HSI should focus on BFlh muscle properties i.e., elasticity and fascicle length for reducing re-injury and increasing sports performance.

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

This study aimed to investigate the effect of an isometric (ISO) or Nordic hamstring exercise (NHE) intervention, alongside a sprint training program on hamstring strength, architecture, and sprinting performance in Australian footballers. Twenty-five male athletes undertook NHE ( n = 13) or ISO ( n = 12) training across a 38-wk period (including preseason and in season). Biceps femoris long head (BFlh) architecture, ISO, and eccentric knee flexor strength were assessed at baseline, at the end of preseason (14 wk), and at the conclusion of the intervention. Sprint times and force-velocity profiles were determined at baseline and at the end of preseason. After the intervention, both groups had significant improvements in BFlh fascicle length (NHE: 1.16 cm, 95% CI = 0.68 to 1.63 cm, d = 1.88, P < 0.001; ISO: 0.82 cm, 95% CI = 0.57 to 1.06 cm, d = 1.70, P < 0.001), muscle thickness (NHE: 0.11 cm, 95% CI = 0.01 to 0.21 cm, d = 0.51, P = 0.032; ISO: 0.21 cm, 95% CI = 0.10 to 0.32 cm, d = 0.86, P = 0.002), and eccentric strength (NHE: 83 N, 95% CI = 53 to 114 N, d = 1.79, P < 0.001; ISO: 83 N, 95% CI = 17 to 151 N, d = 1.17, P = 0.018). Both groups also finished the intervention weaker isometrically than they started (NHE: -45 N, 95% CI = -81 to -8 N, d = -1.03, P = 0.022; ISO: -80 N, 95% CI = -104 to -56 N, d = -3.35, P < 0.001). At the end of preseason, the NHE group had improved their 5-m sprint time by 3.3% ± 2.0%), and their maximum horizontal velocity was 3% ± 2.1% greater than the ISO group who saw no changes. Both ISO and NHE training with a periodized sprinting program can increase BFlh fascicle length, thickness, and eccentric strength in Australian footballers. NHE training also improves 5-m sprint time and maximum velocity. However, both interventions reduced ISO strength. These findings provide unique, contextually relevant insights into the adaptations possible in semiprofessional athletes.

Rugby Players Exhibit Stiffer Biceps Femoris, Lower Biceps Femoris Fascicle Length to Knee Extensors, and Knee Flexors to Extensors Muscle Volume Ratios Than Active Controls.

This study aimed to determine if hamstring-strain-injury risk factors related to muscle structure and morphology differed between rugby union players and controls. The biceps femoris long head (BFlh) fascicle length and passive muscle stiffness and relative and absolute muscle volume of knee flexors (KF) and extensors (KE) were measured in 21 male subelite rugby players and 21 male physically active nonathletes. BFlh fascicle length was significantly longer (mean difference [MD] = 1.6 [1.7]cm) and BFlh passive muscle stiffness was significantly higher in rugby players (MD = 7.8 [14.8]kPa). The absolute BFlh (MD = 71.9 [73.3]cm3), KF (MD = 332.3 [337.2]cm3), and KE (MD = 956.3 [557.4]cm3) muscle volumes were also significantly higher in rugby players. There were no significant differences in the relative BFlh and KF muscle volumes. The relative KE muscle volumes were significantly higher in rugby players (MD = 2.3 [3.7]cm3/kg). However, the percentage BFlh fascicle length:KE (MD = -0.1% [0.1%]), BFlh/KE (MD = -0.9% [1.9%]), and KF:KE (MD = -4.9% [5.9%]) muscle volume ratios were significantly lower in the rugby players. BFlh muscle volume significantly correlated with BFlh fascicle length (r = .59, r2 = .35) and passive muscle stiffness (r = .46, r2 = .21). Future prospective studies should examine whether there are threshold values in BFlh passive muscle stiffness and BFlh fascicle length:KE, BFlh:KE, and KF:KE muscle volume ratios for predicting hamstring strain injuries.

Biceps Femoris Fascicle Behavior during Submaximal and Maximal Slow Speed Contractions.

The present study compared the effects of contraction intensity (submaximal vs maximal) and mode (concentric vs eccentric) on biceps femoris long head (BFlh) fascicle lengthening, rotation, and architectural gear ratio at long and short muscle lengths. Data were captured from 18 healthy adults (10 men and 8 women) without history of right hamstring strain injury. BFlh fascicle length ( Lf ), fascicle angle (FA), and muscle thickness (MT) were assessed in real time using two serially aligned ultrasound devices while submaximal and maximal concentric and eccentric isokinetic knee flexions were performed at 30°·s -1 . Ultrasound videos were exported and edited to create a single, synchronized video, and three fascicles were analyzed through the range of motion (10° to 80°). Changes (Δ) in Lf , FA, MT, and muscle gear at long (60° to 80° knee angle; 0° = full knee extension) and short (10° to 30°) muscle lengths and across the full knee flexion range were measured and compared. Greater Δ Lf was observed at long muscle length ( P < 0.001) during both submaximal and maximal eccentric and concentric contractions. When the full length range was analyzed, a slightly greater ΔMT was observed in concentric contractions ( P = 0.03). No significant differences between submaximal and maximal contractions were observed for Δ Lf , ΔFA, or ΔMT. No changes were detected in the calculated muscle gear between muscle lengths, intensities, or conditions ( P > 0.05). Although gear ratio ranged ~1.0 to 1.1 under most conditions, the increased fascicle lengthening observed at long muscle lengths might influence acute myofiber damage risk but also speculatively play a role in chronic hypertrophic responses to training.

Do Repeated Sprints Affect the Biceps Femoris Long Head Architecture in Football Players with and without an Injury History?-A Retrospective Study.

The aim of this study was to compare the biceps femoris long head (BFlh) architecture between football players with (twelve) and without (twenty) history of BFlh injury before and after a repeated sprint task. Fascicle length (FL), pennation angle (PA) and muscle thickness (MT) were assessed at rest and in the active condition before and after the repeated sprint protocol. Athletes with previous BFlh injury showed shorter FL at rest (p = 0.014; η2p = 0.196) and active state (p &lt; 0.001; η2p = 0.413), and greater PA at rest (p = 0.002; η2p = 0.307) and active state (p &lt; 0.001; η2p = 0.368) before and after the task. Intra-individual comparisons showed that injured limbs have shorter FL at rest (p = 0.012; η2p = 0.519) and in the active state (p = 0.039; η2p = 0.332), and greater PA in passive (p &lt; 0.001; η2p = 0.732) and active conditions (p = 0.018; η2p = 0.412), when compared with contralateral limbs. Injured players, at rest and in the active condition, display shorter BFlh FL and greater PA than contralateral and healthy controls after repeated sprints. Moreover, the BFlh of injured players presented a different architectural response to the protocol compared with the healthy controls.

Effects of changes in optimal muscle fibre length in the biceps femoris long head on muscle force during the late swing phase of maximal speed sprinting: a simulation study

ABSTRACT Hamstring strain injuries would frequently occur during the late swing phase of sprinting, while increasing biceps femoris long head’s (BFlh) fascicle length induced by eccentric contraction exercises can reduce the risk of strain injuries. Thus, using a musculoskeletal modelling simulation, we examined how manipulating BFlh optimal muscle fibre length would change muscle force during the late swing phase of sprinting for providing knowledge preventing hamstring strain injuries. A motion capture system was used to collect kinematic data from 40 male athletes during maximal speed sprinting. Muscle force and force-generating capabilities determined by force-length-velocity properties were estimated with three BFlh optimal muscle fibre lengths (90%, 110% and 120%), which were perturbed from the nominal (100%). During the late swing phase of sprinting, the muscle force and force-generating capabilities, induced by the force-length property rather than the force-velocity property, were increased by increases in BFlh optimal muscle fibre length. Moreover, magnitudes of the simulated increases in muscle force and force-generating capabilities were correlated with the peak BFlh muscle-tendon unit length. These results demonstrate that lengthening BFlh optimal muscle fibre might increase muscle force during the late swing phase, and the magnitude of increment would be associated with increasing muscle-tendon unit length.

Effect of an Isometric or Eccentric Hip Extension Exercise Intervention on Hamstring Strength, Architecture, and Morphology.

This study aimed to investigate hamstring architectural, strength, and morphological adaptations after an eccentric or isometric hip extension exercise intervention. Twenty-four recreationally active males performed either an eccentric ( n = 12) or an isometric hip extension ( n = 12) exercise intervention, twice per week for 6 wk, followed by a 4-wk detraining period. Biceps femoris long head (BFlh) architecture was assessed pre-intervention, mid-intervention, post-intervention, and post-detraining via two-dimensional ultrasound. Strength was assessed pre-intervention, post-intervention, and post-detraining during an isokinetic knee flexion, an isometric hip extension, a Nordic hamstring exercise, and a single-leg hamstring bridge repetition to fatigue test. Hamstring muscle morphology was assessed via magnetic resonance imaging before strength testing sessions. The eccentric hip extension exercise intervention significantly lengthened BFlh fascicles (+19.7%, P < 0.001, d = 1.57), increased eccentric knee flexion torque (ECC 60°·s -1 , +12%, P < 0.005, d = 0.66; ECC 180°·s -1 , +8.3%, P < 0.05, d = 0.41), and increased BFlh (+13.3%, P < 0.001, d = 1.96) and semimembranosus (SM) muscle volume (+12.5%, P < 0.001, d = 2.25). After 4 wk of detraining, BFlh fascicles were significantly shortened in the eccentric group (-14.8%, P < 0.005, d = -1.25), whereas eccentric knee flexion torque and BFlh and SM volumes were unchanged. The isometric hip extension exercise intervention significantly increased isometric knee flexion torque (+10.4%, P < 0.05, d = 0.54), isometric hip extension force (+12.4%, P < 0.05, d = 0.41), and semitendinosus volume (+15%, P = 0.054, d = 1.57). All other outcome measures saw no significant changes. After 4 wk of detraining, no significant changes to any variables were observed in the isometric group. The eccentric but not isometric hip extension exercise intervention significantly increased BFlh fascicle length. Both exercise interventions demonstrated contraction mode-specific increases in strength. However, the eccentric hip extension exercise intervention resulted in preferential hypertrophy of BFlh and SM, and the isometric hip extension exercise intervention led to selective hypertrophy of semitendinosus.

Isometric fascicle behaviour of the biceps femoris long head muscle during Nordic hamstring exercise variations

ObjectivesTo compare biceps femoris long head (BFlh) muscle tendon unit and fascicle function during Nordic hamstring exercise (NHE) variations with different hip range of motion. DesignCross-sectional. MethodsTwelve healthy volunteers (age: 24 ± 4 years; mass: 77 ± 6 kg; height: 177 ± 4 cm) performed two NHE variations: NHE with hips in neutral (fixed) position (conventional NHE); and NHE with hip flexion/extension. BFlh fascicle length behaviour was assessed using a dual transducer ultrasound configuration. BFlh and semitendinosus muscle electromyography, lower limb kinematics and knee flexion moment were also recorded. A biomechanical model was used to estimate BFlh muscle-tendon unit (MTU) length. Statistical Parametric Mapping was used to assess timing differences in outcome variables across the movement. ResultsIn both variations, during much of the exercise (~30–80% of movement phase), BFlh fascicles undergo little length change (isometric) while the MTU lengthens. Fascicles stretched considerably just in the last ~20% of the exercise, and changes in fascicle length (<2 cm stretch) were smaller in comparison to changes in MTU length (<4 cm stretch). Hip flexion resulted in the muscle tendon unit and fascicles operating at longer lengths until approximately 80% of the movement phase. ConclusionsThe decoupling between fascicle and MTU length seen during the NHE variations suggests that stretch of the elastic tissue of the MTU has an important role in absorbing energy during Nordic hamstring exercises. This may be important when considering adaptations to BFlh muscle and connective tissues that might occur from NHE training.

The Dose-Response of the Nordic Hamstring Exercise on Biceps Femoris Architecture and Eccentric Knee Flexor Strength: A Randomized Interventional Trial.

To examine the dose-response of the Nordic hamstring exercise (NHE) on biceps femoris long head (BFlh) architecture and eccentric knee flexor strength. Randomized interventional trial. Forty recreationally active males completed a 6-week NHE training program consisting of either intermittent low volumes (group 1; n = 10), low volumes (group 2; n = 10), initial high volumes followed by low volumes (group 3; n = 10), or progressively increasing volumes (group 4; n = 10). A 4-week detraining period followed each program. Muscle architecture was assessed weekly during training and after 2 and 4weeks of detraining. Eccentric knee flexor strength was assessed preintervention and postintervention and after 2 and 4weeks of detraining. Following 6weeks of training, BFlh fascicle length (FL) increased in group 3 (mean difference = 0.83cm, d = 0.45, P = .027, +7%) and group 4 (mean difference = 1.48cm, d = 0.94, P = .004, +14%). FL returned to baseline following detraining in groups 3 and 4. Strength increased in group 2 (mean difference = 53.6N, d = 0.55, P = .002, +14%), group 3 (mean difference = 63.4N, d = 0.72, P = .027, +17%), and group 4 (mean difference = 74.7, d = 0.83, P = .006, +19%) following training. Strength returned to baseline following detraining in groups 2 and 3 but not in group 4. Initial high volumes of the NHE followed by lower volumes, as well as progressively increasing volumes, can elicit increases in BFlh FL and eccentric knee flexor strength. Low volumes of the NHE were insufficient to increase FL, although as few as 48 repetitions in 6 weeks did increase strength.

Early Changes of Hamstrings Morphology and Contractile Properties during 10 d of Complete Inactivity.

The hamstrings (HS) muscle group plays a fundamental role in maintaining knee stability, thus contributing to the prevention and rehabilitation of lower limb musculoskeletal injuries. However, little is known about HS structural and functional adaptations after periods of prolonged inactivity. Our purpose was to investigate the HS morphological and contractile properties changes during 10 d of bed rest (BR). Ten young healthy males underwent a 10-d BR. HS cross-sectional area (CSA) (at 30%, 50%, and 70% of femur length) and biceps femoris long head (BFlh) architecture were assessed by ultrasound imaging after 0 d (BR0), 2 d (BR2), 4 d (BR4), 6 d (BR6), and 10 d (BR10) of BR, whereas BFlh contractile properties (radial twitch displacement [Dm] and contraction time [Tc]) were evaluated at the same time points by tensiomyography. HS muscle volume was assessed by magnetic resonance imaging at BR0 and BR10. A reduction in muscle volume was observed in BFlh ( P = 0.002; Δ = -3.53%), biceps femoris short head ( P = 0.002; Δ = -3.54%), semitendinosus ( P = 0.002; Δ = -2.63%), semimembranosus ( P = 0.002; Δ = -2.01%), and HS pooled together ( P < 0.001; Δ = -2.78%). Early changes in CSA were detected at 30% femur length already at BR6 for BFlh ( P = 0.009; Δ = -2.66%) and biceps femoris short head ( P = 0.049; Δ = -1.96%). We also found a reduction in fascicle length at BR6 ( P = 0.035; Δ = -2.44%) and BR10 ( P < 0.001; Δ = -2.84%). Dm and Tc increased at BR2 ( P = 0.010; Δ = 30.0%) and B10 ( P = 0.019; Δ = 19.7%), respectively. Despite being a nonpostural muscle group, HS exhibited a moderate reduction in muscle dimensions in response to a short unloading period. Small changes in BFlh fascicle length were also observed, accompanied by alterations in BFLh contractile properties. These HS modifications should not be ignored from a clinical perspective.

Is Muscle Architecture Different in Athletes with a Previous Hamstring Strain? A Systematic Review and Meta-Analysis.

Hamstring strains are a frequent injury in sports and are characterized by a high recurrence rate. The aim of this review was to examine the muscle and tendon architecture in individuals with hamstring injury. A systematic literature search in four databases yielded eleven studies on architecture following injury. Differences in the fascicle length (FL), pennation angle (PA) and muscle size measures (volume, thickness and physiological cross-sectional area) at rest were not significantly different between the previously injured limb and the contralateral limb (p > 0.05). There was moderate evidence that biceps femoris long head (BFlh) FL shortening was greater during contraction in the injured compared to the contralateral limb. The BFlh FL was smaller in athletes with a previous injury compared to uninjured individuals (p = 0.0015) but no differences in the FL and PA of other muscles as well as in the aponeurosis/tendon size were observed (p > 0.05). An examination of the FL of both leg muscles in individuals with a previous hamstring strain may be necessary before and after return to sport. Exercises that promote fascicle lengthening of both injured and uninjured leg muscles may be beneficial for athletes who recover from a hamstring injury.

Biceps femoris long head sarcomere and fascicle length adaptations after 3 weeks of eccentric exercise training

BackgroundEccentric exercise increases muscle fascicle lengths; however, the mechanisms behind this adaptation are still unknown. This study aimed to determine whether biceps femoris long head (BFlh) fascicle length increases in response to 3 weeks of eccentric exercise training are the result of an in-series addition of sarcomeres within the muscle fibers. MethodsTen recreationally active participants (age = 27 ± 3 years; mass = 70 ± 14 kg; height = 174 ± 9 cm; mean ± SD) completed 3 weeks of Nordic hamstring exercise (NHE) training on a custom exercise device that was instrumented with load cells. We collected in vivo sarcomere and muscle fascicle images of the BFlh in 2 regions (central and distal) by using microendoscopy and 3 dimension ultrasonography. We then estimated sarcomere length, sarcomere number, and fascicle length before and after the training intervention. ResultsEccentric knee flexion strength increased after the training (15%; p < 0.001; ηp2 = 0.75). Further, we found a significant increase in fascicle length (21%; p < 0.001; ηp2 = 0.81) and sarcomere length (17%; p < 0.001; ηp2 = 0.90) in the distal but not in the central portion of the muscle. The estimated number of sarcomeres in series did not change in either region. ConclusionFascicle length adaptations appear to be heterogeneous in the BFlh in response to 3 weeks of NHE training. An increase in sarcomere length, rather than the addition of sarcomeres in series, appears to underlie increases in fascicle length in the distal region of the BFlh. The mechanism driving regional increases in fascicle and sarcomere length remains unknown, but we speculate that it may be driven by regional changes in the passive tension of muscle or connective tissue adaptations.

M. Biceps Femoris Long Head Architecture and Sprint Ability in Youth Soccer Players.

Hamstring muscle architecture may be associated with sprint performance and the risk of sustaining a muscle injury, both of which increase during puberty. In this study, we investigated the m. biceps femoris long head (BFlh) cross-sectional area (ACSA), fascicle length (FL) and pennation angle (PA), and sprint performance as well as their relationship in under 13 to 15 youth soccer players. We measured 85 players in under-13 (n = 29, age = 12.5 [0.1]y, height = 155.3 [6.2]cm, weight = 43.9 [7.6]kg), under-14 (n = 25, age = 13.5 [0.3]y, height = 160.6 [7.7]cm, weight = 47.0 [6.8]kg), and under-15 (n = 31, age = 14.4 [0.3]y, height = 170.0 [7.7]cm, weight = 58.1 [8.8]kg) teams. We used ultrasound to measure BFlh ACSA, FL and PA, and sprint tests to assess 10- and 30-m sprint time, maximal velocity (vmax), and maximal acceleration (αmax). We calculated Pearson r to assess the relationship between sprint ability and architectural parameters. All muscle architectural parameters increased from the under-13 to the under-15 age group (BFlh ACSA = 37%, BFlh FL = 11%, BFlh PA = 8%). All sprint performance parameters improved from the under-13 to under-15 age categories (30-m time = 7%, 10-m time = 4%, vmax = 9%, αmax = 7%). The BFlh ACSA was correlated with 30-m sprint time (r = -.61 (95% compatibility interval [CI] [-.73, -.45]) and vmax (r = .61, 95% CI [.45, .72]). A combination of BFlh ACSA and age best predicted 30-m time (R² = .47 [.33, .62]) and 10-m time (R² = .23 [.08, .38]). Muscle architectural as well as sprint performance parameters increase from the under-13 to under-15 age groups. Even though we found correlations for all assessed architectural parameters, BFlh ACSA was best related to the assessed sprint parameters.

Sprinting, Strength, and Architectural Adaptations Following Hamstring Training in Australian Footballers.

The aim of this study was to determine the sprinting, strength, and architectural adaptations following a hip-dominant flywheel (FLY) or Nordic hamstring exercise (NHE) intervention in Australian footballers. Twenty-seven male athletes were randomized to FLY (n=13) or NHE (n=14) training across a 39-week period (inclusive of pre-season and in-season). Biceps femoris long head (BFlh) architecture was assessed throughout. Eccentric hamstring strength and 40m sprint times (with force-velocity profiling) were assessed at baseline, end of pre-season, and following the intervention. After the intervention, BFlh fascicle length was longer in both groups compared to baseline (FLY: 1.16cm, 95%CI: 0.66 to 1.66cm, d=1.99, p<0.001; NHE: 1.08cm, 95%CI: 95%CI 0.54 to 1.61cm, d=1.73, p<0.001). Both groups also increased their eccentric strength (FLY: mean change 82N, 95%CI 12 to 152N, d=1.34, p=0.026; NHE: mean change 97N, 95%CI 47 to 146N, d=1.77, p=0.001). After pre-season, the NHE group improved their 5m sprint time by 3.5% (±1.2%) and were 3.7% (±1.4%) and 2.0% (±0.5%) faster than the FLY group across 5m and 10m, respectively. At the end of pre-season, the FLY group improved maximal velocity by 3.4% (±1.4%) and improved horizontal force production by 9.7% in-season (±2.2%). Both a FLY and NHE intervention increase BFlh fascicle length and eccentric strength in Australian Footballers. An NHE intervention led to enhanced acceleration capacity. A FLY intervention was suggested to improve maximal sprint velocity and horizontal force production, without changes in sprint times. These findings have implications for hamstring injury prevention but also programs aimed at improving sprint performance.

Hamstring strength and architectural adaptations following inertial flywheel resistance training

ObjectivesTo investigate the architectural and strength adaptations of the hamstrings following 6-weeks of inertial flywheel resistance training. DesignRandomised, stratified training intervention MethodsTwenty healthy males undertook 6-weeks of a conventional (n=10) or eccentrically biased (n=10) flywheel leg-curl training intervention as well as a subsequent 4-week detraining period. Biceps femoris long head (BFlh) architecture was assessed weekly, whilst assessments of eccentric and isometric knee flexor strength and rate of force development (RFD) were conducted prior to and following the intervention and detraining periods. ResultsThe participants who undertook the eccentrically biased flywheel intervention showed a significant 14±5% (p<0.001, d=1.98) increase in BFlh fascicle length after 6-weeks of training. These improvements in fascicle length subsequently declined by 13±4% (p<0.001. d=-2.04) following the 4-week detraining period. The conventional flywheel leg-curl training group saw no changes in BFlh fascicle length after the intervention (-0.5%±0.8%, p=0.939, d=-0.04) or detraining (-1.1%±1%, p=0.984, d=-0.03) periods. Both groups saw no changes in any of the strength or RFD variables after the intervention or the detraining period. ConclusionsFlywheel leg-curl training performed with an eccentric bias led to significant lengthening of BFlh fascicles without a change in RFD, eccentric or isometric strength. These increases in fascicle length were lost following a 4-week detraining period. Conventional flywheel leg-curl training resulted in no changes in fascicle length, strength and RFD. These findings suggest that additional eccentric bias is required during inertial flywheel resistance training to promote fascicle lengthening in the BFlh, however this may still be insufficient to cause alterations to strength and RFD.

Sprint versus isolated eccentric training: Comparative effects on hamstring architecture and performance in soccer players.

AimsThe purpose of this study was to compare the effects of hamstring eccentric (NHE) strength training versus sprint training programmed as complements to regular soccer practice, on sprint performance and its mechanical underpinnings, as well as biceps femoris long head (BFlh) architecture.MethodsIn this prospective interventional control study, sprint performance, sprint mechanics and BFlh architecture variables were compared before versus after six weeks of training during the first six preseason weeks, and between three different random match-pair groups of soccer players: “Soccer group” (n = 10), “Nordic group” (n = 12) and “Sprint group” (n = 10).ResultsFor sprint performance and mechanics, small to large pre-post improvements were reported in “Sprint group” (except maximal running velocity), whereas only trivial to small negative changes were reported in “Soccer group” and “Nordic group”. For BFlh architecture variables, “Sprint” group showed moderate increase in fascicle length compared to smaller augment for the “Nordic” group with trivial changes for “Soccer group”. Only “Nordic” group presented small increases at pennation angle.ConclusionsThe results suggest that sprint training was superior to NHE in order to increase BFlh fascicle length although only the sprint training was able to both provide a preventive stimulus (increase fascicle length) and at the same time improve both sprint performance and mechanics. Further studies with advanced imaging techniques are needed to confirm the validity of the findings.

Ultrasound-derived Biceps Femoris Long Head Fascicle Length: Extrapolation Pitfalls.

This study aimed to compare biceps femoris long head (BFlh) fascicle length (Lf) obtained with different ultrasound-based approaches: 1) single ultrasound images and linear Lf extrapolation, 2) single ultrasound images and one of two different trigonometric equations (termed equations A and B), and 3) extended field of view (EFOV) ultrasound images. Thirty-seven elite alpine skiers (21.7 ± 2.8 yr) without a previous history of hamstring strain injury were tested. Single ultrasound images were collected with a 5-cm linear transducer from BFlh at 50% femur length and were compared with whole muscle scans acquired by EFOV ultrasound. The intrasession reliability (intraclass correlation coefficient [ICC3,k]) of Lf measurements was very high for both single ultrasound images (i.e., Lf estimated by linear extrapolation; ICC3,k = 0.96-0.99, SEM = 0.18 cm) and EFOV scans (ICC3,k = 0.91-0.98, SEM = 0.19 cm). Although extrapolation methods showed cases of Lf overestimation and underestimation when compared with EFOV scans, mean Lf measured from EFOV scans (8.07 ± 1.36 cm) was significantly shorter than Lf estimated by trigonometric equations A (9.98 ± 2.12 cm, P < 0.01) and B (8.57 ± 1.59 cm, P = 0.03), but not significantly different from Lf estimated with manual linear extrapolation (8.40 ± 1.68 cm, P = 0.13). Bland-Altman analyses revealed mean differences in Lf obtained from EFOV scans and those estimated from equation A, equation B, and manual linear extrapolation of 1.91 ± 2.1, 0.50 ± 1.0, and 0.33 ± 1.0 cm, respectively. The typical extrapolation methods used for estimating Lf from single ultrasound images are reliable within the same session, but not accurate for estimating BFlh Lf at rest with a 5-cm field of view. We recommend that EFOV scans are implemented to accurately determine intervention-related Lf changes in BFlh.

Pain-Free Versus Pain-Threshold Rehabilitation Following Acute Hamstring Strain Injury: A Randomized Controlled Trial.

Randomized controlled trial. Conventional guidelines recommend hamstring strain injury (HSI) rehabilitation should only be performed and progressed in complete absence of pain, despite lack of comparison to alternative approaches. The primary aim of this study was to compare the number of days from acute HSI to return to play (RTP) clearance following a standardised rehabilitation protocol performed within either pain-free or pain-threshold limits. The secondary aims were to compare isometric knee flexor strength, biceps femoris long head (BFlh) fascicle length, fear of movement and re-injury during a six-month follow-up between pain-free and pain-threshold groups. Forty-three men with acute HSIs were randomly allocated to either a pain-free (n=22) or pain-threshold (n=21) rehabilitation group. Days from HSI to RTP clearance, isometric knee flexor strength, BFlh fascicle length, fear of movement and re-injuries within six-month follow-up were reported. The median time from HSI to RTP clearance was 15 days (95% CI = 13 to 17) in the pain-free group and 17 days (95% CI = 11 to 24) in the pain-threshold group, which was not significantly different (p = 0.37). Recovery of isometric knee flexor strength at 90/90 degrees of hip/knee flexion was greater in the pain-threshold group at RTP clearance by 15% (95% CI = 1 to 28) and by 15% (95% CI = 1 to 29) at two-month follow-up. BFlh fascicles were 0.91cm (95% CI = 0.34 to 1.48) longer at two-month follow-up in the pain-threshold group. Two re-injuries occurred in both the pain-free and pain-threshold group during six-month follow-up. Pain-threshold rehabilitation did not accelerate RTP clearance but did result in greater recovery of isometric knee flexor strength and better maintenance of BFlh fascicle length improvements compared to pain-free rehabilitation. J Orthop Sports Phys Ther, Epub 28 Jun 2019. doi:10.2519/jospt.2019.8895.

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

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. Thirty recreationally active males performed a total of 128 reps of NHEbodyweight (n=10), NHEweighted (n=10), or RHCweighted training (n=10) across 6weeks. Following the intervention, participants avoided any eccentric training for 4weeks (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. For the NHEweighted group, NHE strength increased (+81N, P=0.044, d=0.90) and BFlh fascicles lengthened (+1.57cm, P<0.001, d=1.41) after 6weeks of training. After 1week of detraining, BFlh fascicle lengths shortened, with the largest reductions seen in the NHEweighted group (-0.96cm, 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. NHEweighted interventions induce large BFlh fascicle lengthening responses and these adaptations decay after just 1week 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.

Poor agreement between ultrasound and inbuilt diffusion tensor MRI measures of biceps femoris long head fascicle length

Objectives This study aimed to determine whether diffusion tensor MR imaging (DTI) methodology inbuilt within manufacturer software can reliably measure biceps femoris long head (BFlh) fascicle length (FL) and to investigate agreement between ultrasound (US) measures and inbuilt DTI measures of BFlh FL. Methods Both legs of 20 males were examined (40 legs). FL of the BFlh was determined utilizing two-dimensional ultrasound and diffusion tensor MRI assessment. Results Reliability of DTI measures of BFlh FL was found to be acceptable (ICC: 0.804; 95% CI: 0.482 to 0.926); however, minimal detectable change (MDC) values were found to be clinically unacceptable (3.5 cm). Poor agreement was found between US and DTI measures of BFlh FL (ICC: 0.096; MDC: 4.1 cm; Mean bias (limits of agreement): 0.31 cm (−2.74 to 3.36 cm)). Conclusions Diffusion tensor MR imaging measures inbuilt within manufacturer software of BFlh fascicle length do not display clinically acceptable reliability nor do they agree with validated US-derived measures. In practice, either US measures should continue to be implemented or with the available expertise, algorithm-based DTI-derived measures should be utilized to measure BFlh FL.