Knee and hip joint dynamics differ between sprinting and Nordic hamstring exercises.

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)...

ObjectivesTo compare the electromyographic activity of the Biceps femoris long head and Semitendinosus muscles during bilateral and unilateral isometric Nordic hamstring exercise performed on an inclined platform at different knee flexion angles between leg side with and without a history of hamstring strain injury.MethodsTen physically active male volunteers with a history of hamstring strain injury in either leg performed isometric Nordic hamstring exercise, maintaining the exercise position for 5 s under the following conditions: (1) bilateral, 150° knee angle on a 50° inclined platform (BL50); (2) bilateral, 140° knee angle on a 40° inclined platform (BL40); (3) unilateral, 150° knee angle on a 50° inclined platform (UL50); and (4) unilateral, 140° knee angle on a 40° inclined platform (UL40). External torque on the knee joint was controlled to ensure equivalence across conditions. Electromyographic activity of the Biceps femoris long head, Semitendinosus, and related muscles was measured in both legs with and without a history of hamstring strain injury.ResultsThe Biceps femoris long head muscle demonstrated significantly higher electromyographic activity during the unilateral Nordic hamstring exercise tasks, irrespective of hamstring strain injury history (p < 0.05). The Biceps femoris long head electromyographic activity was higher than Semitendinosus activity only in unilateral Nordic hamstring exercise conditions.. Additionally, no significant differences in the electromyographic activity were observed across the different slope angles when the external torque at the knee joint was matched (p > 0.05).ConclusionsThese findings suggest that performing isometric unilateral Nordic hamstring exercise at shallow knee flexion angles preferentially enhances the muscle activation of biceps femoris long head muscle regardless of hamstring strain injury history.

BackgroundThe hamstrings are an important muscle group that contribute to horizontal force during sprint acceleration and are also the most injured muscle group in running-based sports. Given the significant time loss associated with hamstrings injury and impaired sprinting performance following return to sport, identifying exercises that drive adaptations that are both protective of strain injury and beneficial to sprint performance is important for the strength and conditioning professional. This paper describes the study protocol investigating the effects of a 6-week training program using either the hip-dominant Romanian deadlift (RDL) or the knee-dominant Nordic hamstring exercise (NHE) on hamstring strain injury risk factors and sprint performance.MethodsA permuted block randomized (1:1 allocation) intervention trial will be conducted involving young, physically-active men and women. A target sample size of 32 will be recruited and enrolled participants will undergo baseline testing involving extended-field-of-view ultrasound imaging and shear wave elastography of the biceps femoris long head muscle, maximal hamstrings strength testing in both the RDL and NHE, and on-field sprint performance and biomechanics. Participants will complete the 6-week training intervention using either the RDL or NHE, according to group allocation. Baseline testing will be repeated at the end of the 6-week intervention followed by 2 weeks of detraining and a final testing session. The primary outcome will be regional changes in fascicle length with secondary outcomes including pennation angle, muscle cross sectional area, hamstring strength, and maximal sprint performance and biomechanics. An exploratory aim will determine changes in shear wave velocity.DiscussionDespite extensive research showing the benefits of the NHE on reducing hamstring strain injury risk, alternative exercises, such as the RDL, may offer similar or potentially even greater benefits. The findings of this study will aim to inform future researchers and practitioners investigating alternatives to the NHE, such as the RDL, in terms of their effectiveness in reducing rates of hamstring strain injury in larger scale prospective intervention studies.Trial RegistrationThe trial is prospectively registered on ClinicalTrials.gov (NCT05455346; July 15, 2022).

Akyürek, TA, Ertan, H, and Darendeli, A. Biceps femoris EMG activity during incline treadmill running and nordic hamstring task. J Strength Cond Res 39(5): 540-546, 2025-Although the Nordic hamstring exercise (NHE) is an effective method for strengthening the knee flexors, untrained individuals or intermediate level athletes may have difficulty performing it. In this study, we propose incline treadmill running as an alternative knee flexor exercise. The aim of this study was to compare the biceps femoris (BF) muscle activity (electromyography, EMG) levels between NHE and 10% grade treadmill running at 3 speeds. Nineteen recreationally active men were recruited for the study. Maximum voluntary contraction (MVC) with the knee flexors were completed. Nordic hamstring exercise and 10% grade treadmill running tasks were performed in a randomized counterbalanced order. Biceps femoris EMG activity was recorded during the measurements. Statistical significance was set to p < 0.05. We found that the peak EMG amplitude for BF was higher during the NHE (∼63% MVC) than during treadmill running at a 10% grade across low-to-moderate speeds. Increasing the running speed from 3.61 m·s -1 to 4.16 m·s -1 (∼49% MVC) raised the peak EMG amplitude by approximately 10% MVC. In addition, the variability in EMG amplitude for BF was greater during 10% grade treadmill running than during NHE. Although the peak EMG activity was greater during the NH task, it reached comparable levels when performing 10% grade treadmill running at a moderate running speed. Our results suggest that incline treadmill running can be an alternative knee flexor exercise that can be individualized by adjusting treadmill grade and speed, particularly for untrained individuals.

The Nordic hamstring exercise (NHE) has commonly been investigated in isolation, however, within practice multiple modalities are commonly incorporated. However, the NHE has a low level of compliance within sport, with sprinting being potentially being preferred. The present study aimed to observe the effect of a lower-limb program with either additional NHE or sprinting on the modifiable risk factors hamstring strain injury (HSI) and athletic performance. 38 collegiate athletes were randomly assigned into three groups: control standardised lower-limb training program (n = 10 (2 female, 8 male), age = 23.50 ± 2.95 years, height = 1.75 ± 0.09 m, mass 77.66 ± 11.82 kg), additional NHE (n = 15 (7 female, 8 male), age = 21.40 ± 2.64 years, height = 1.74 ± 0.04 m, mass 76.95 ± 14.20 kg) and additional sprinting (n = 13 (4 female, 9 male), age = 22.15 ± 2.54 years, height = 1.74 ± 0.05 m, mass 70.55 ± 7.84 kg). All participants performed a standardised lower-limb training program twice per week for seven weeks, including Olympic lifting derivatives, squatting movements, and the Romanian deadlift, with experimental groups performing with either additional sprinting or NHE. Bicep femoris architecture, eccentric hamstring strength, jump performance, lower-limb maximal strength and sprint ability were measured pre and post. All training groups demonstrated significant (p < 0.001), small-moderate increases in Bicep femoris architecture (g = 0.60–1.22), with significant (p < 0.001), small-large increases in absolute and relative eccentric peak force (g = 0.60–1.84). Significant and small increases were observed in take-off velocity and mean propulsion force (p < 0.02, g = 0.47–0.64), with non-significant and small increases for both the sprint and control training groups for mean propulsion force (p > 0.05, g = 0.42–0.50). Nordic and sprint training groups had significant and small increases in peak absolute and relative net force (p < 0.001, g = 0.44–0.60). The control group had a non-significant trivial increase in absolute peak net force (p > 0.05, g = 0.22), with a significant and small increase in relative peak relative net force (p = 0.034, g = 0.48). Significant and small decreases for the NHE and sprinting training groups was observed for 0–10 m, 0–20 m, and 10–20 m sprint time (p < 0.010, g = 0.47–0.71). Performing multiple modalities, with either additional NHE or sprinting, as part of a complete resistance training program was superiorly effective for measures of modifiable risk factors HSI, with similar increases observed in measures of athletic performance derived from the standardised lower-limb training program.

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.

Influence of trunk flexion on hip and knee joint kinematics during a controlled drop landing

Comprehensive analysis of ankle, knee, and hip kinematics and kinetics during anterior lunge performance in young adults has not been studied. In addition, the effects of adding external resistance on the kinematics and kinetics are unknown. To determine the effects of external load on ankle, knee, and hip joint kinematics and kinetics during the anterior lunge. Crossover study. Laboratory environment. A total of 16 recreationally active, college-aged adults (8 men, 8 women). Anterior lunges under 4 external-load conditions, 0% (control), 12.5%, 25%, and 50% of body mass. Ankle, knee, and hip peak flexion, net joint extensor moment impulse, and eccentric and concentric work were computed during the interval when the stepping limb was in contact with the ground. Additionally, 3 summary lunge characteristics were calculated. No significant (P > .05) load effects were noted for peak flexion angles or the lunge characteristics except for peak vertical total-body center-of-mass displacement. Trend analysis of significant condition-by-joint interactions revealed significant linear trends for all 3 joints, with the hip greater than the ankle and the ankle greater than the knee. Additionally, as the external load increased, mechanical work increased linearly at the hip and ankle but not at the knee. From a kinematic perspective, the lunge involves greater motion at the knee, but from a kinetic perspective, the anterior lunge is a hip-extensor-dominant exercise. Adding external weight prompted the greatest joint kinetic increases at the hip and ankle, with little change in the knee contributions. These results can assist clinicians in deciding whether the characteristics of the anterior lunge match a patient's exercise needs during rehabilitation and performance-enhancement programs.

Eccentric strength training alters muscle architecture, but it is also an important factor for the prevention of hamstring injuries. The purpose was to determine the architectural adaptations of the biceps femoris long head (BFlh) after eccentric strength training with nordic hamstring exercise (NHE), followed by a subsequent detraining period. The participants in this intervention (n=23) completed a period of 13weeks consisting of a first week of control and prior training, followed by 8weeks of eccentric strength training with NHE, and concluding with a 4-week period of detraining. The architectural characteristics of the BFlh were measured at rest using two-dimensional ultrasound before (M1-week 1) and after (M2-week 9) the eccentric strength training, and at the end of the detraining period (M3-week 13). The muscle fascicle length significantly increased (t=-7.73, d=2.28, P<.001) in M2 compared to M1, as well as the muscle thickness (t=-5.23, d=1.54, P<.001), while the pennation angle presented a significant decrease (t=7.81, d=2.3, P<.001). The muscle fascicle length decreased significantly (t=6.07, d=1.79, P<.001) in M3 compared to M2, while the pennation angle showed a significant increase (t=-4.63, d=1.36, P<.001). The results provide evidence that NHE may cause alterations in the architectural conditions of the BFlh and may have practical implications for injury prevention and rehabilitation programs.

PurposeHamstring injuries, particularly in the proximal Biceps femoris long head (BFlh), remain frequent in sports involving sprints and accelerations despite extensive research. Non-uniform muscle activity may contribute to these injuries by causing uneven load distribution. This study examines spatial homogeneity of muscle activity and amplitude in the proximal and distal BFlh at different knee flexion torque levels and muscle-tendon unit (MTU) lengths under controlled isometric conditions.MethodsFifteen male recreational athletes performed unilateral isometric knee flexion contractions at three MTU lengths (0°, 45°, 90° hip flexion) and torque levels (30% MVC90, 60% MVC90, 90%MVC90) with high-density surface electromyography (HDsEMG) assessing proximal and distal activity.ResultsThe proximal BFlh exhibited lower spatial homogeneity and amplitude compared to the distal region across all conditions, with the largest homogeneity differences at lower torques and longer MTU lengths. Proximal homogeneity increased with torque and decreased with MTU length, while the distal region remained consistent. Amplitudes were lower proximally and decreased with MTU length in both regions.ConclusionThe proximal–distal differences in spatial homogeneity and amplitude within the BFlh reflect non-uniform activation patterns along the BFlh and the proximal regions lower spatial homogeneity and amplitude of activation reflect non-uniform patterns, possibly contributing to injury risk.

Background: Hamstring strain injury is a non-contact injury caused by high-speed running.Two of risk factors that of HIS is due to lack of eccentric power of the hamstring muscle and the length of the biceps femoris fascicle.This study to aobserve the effect of nordic hamstring exercise on peak torque eccentric hamstring strength & length of biceps femoris fascicle.Method: Literature search using three databases PubMed, ScienceDirect and SPORTDiscus.In this systematic review and meta-analysis uses randomized control trial (RCT) was used by dividing two groups, namely the intervention group and the control group.Assessment of study quality and risk of bias using the cochrane scale.Results: Six articles were Included in this systematic review and meta-analysis, of which four articles were observed of hamstring muscle eccentric strength and three articles were observed of biceps femoris fascicle length.The eccentric strength showed that there was a significant difference in value (P = 0.009) while for the length of the biceps femoris fascicle, there was no significant difference in value (P = 0.41).Conclusion: Nordic hamstring exercises can increase the eccentric strength of the hamstring muscles, but not the length of the biceps femoris fascicle.

BackgroundNeuromuscular and kinematic peculiarities in the lower extremities between the sexes could influence the way the posterior kinetic chain interacts during exercises and sprinting, potentially altering hamstring strengthening exercise selection.PurposeThis study compared sex-differences in four exercises (the rocker, perpetuum mobile fast and slow [PMfast and PMslow] and the Nordic Hamstring exercise) on their potential to simulate sprint-like muscle activity and kinematics.MethodsMuscle activity of the posterior kinetic chain (biceps femoris [BFlh], semitendinosus [ST], gluteus maximus [GMax] and gastrocnemius medialis [GCM]) was measured with surface electromyography (sEMG) during each exercise and treadmill running at 75% of the individual maximal sprint velocity. sEMG data was normalized to maximal sprinting. 3D-motion capture was employed to assess hip and knee angles.ResultsEight male and 12 female athletes were included (age: 22.4 years ± 3.1; body mass: 61.0 kg ± 7.1; height: 1.67 m ± 0.07). Peak (MD: 31, p= 0.003, [95%CI: 14-48], SMD: 1.1) and average hamstring activity (MD: 16, p< 0.001, [95%CI: 8-24], SMD: 1.4) was greater in females for every examined task. A sex and muscle interaction showed that females displayed significantly greater peak (MD: 39, p=0.002, [95%CI: 21-60], SMD: 1.3) and mean activity (MD: 20, p< 0.001, [95%CI: 12-29], SMD: 1.5) for ST but not BFlh. Joint angles of peak muscle activity showed significantly greater hip angles during the PMfast in females (MD: 30°, p= 0.014, [95%CI: 15-46°], SMD: 2.1) and an overall significantly smaller knee flexion angle for the ST compared to the BFlh (MD: 7°, p= 0.02, [95%CI: 1-12°], SMD: 0.4). Neither hamstring elongation stress nor muscle selectivity showed significant sex differences.DiscussionAside from overall display of greater hamstring, specifically ST activity in all tasks for females, only minor kinematic and no synergist muscle sex-differences were found. Further research exploring sex-specific hamstring neuromuscular strategies is needed.Level of evidence3b

This study aimed to verify the hamstring flexibility, strength, and fascicle length of football (soccer) players with and without history of hamstring strain injury (HSI) in the prior season. Eighty male football players (45 from senior category and 35 from under-20 category) were included in this case–control trial: 20 with history of unilateral HSI in the prior season, and 60 free of HSI in the prior season. Passive straight-leg raise (PSLR) test, isokinetic dynamometry, and biceps femoris long head (BFLH) ultrasonography were performed at preseason to identify risk factors for HSI. No significant differences were found between injured and uninjured limbs of the previously injured players for any outcome (p > 0.05; trivial effect sizes). Uninjured players had higher values than both injured and uninjured limbs of previously injured players for hamstring-to-quadriceps (H/Q) conventional and functional ratios (p < 0.05; medium effect sizes), as well as BFLH fascicle length (p < 0.05; small to medium effect sizes). Football players that had sustained unilateral HSI in the prior season demonstrated lower H/Q strength ratios and shorter BFLH fascicles in both limbs compared to uninjured players.

Early introduction of high-intensity eccentric loading into hamstring strain injury rehabilitation

The aim of this study was to compare the musculature activity and kinematics of knee and hip joints during front and back squat with maximal loading. Two-dimensional kinematical data were collected and electromyographic activities of vastus lateralis, vastus medialis, rectus femoris, semitendinosus, biceps femoris, gluteus maximus and erector spinae were measured while participants (n = 12, 21.2 ± 1.9 years old) were completing front and back squat exercises with maximum loading. Paired sample t-test was used for comparisons between two techniques. Results showed that the electromyographic activity of vastus medialis was found to be greater in the front squat compared to the back squat during the ascending phase (P < 0.05, d = 0.62; 95% CI, −15.0/−4.17) and the whole manoeuvre (P < 0.05, d = 0.41; 95% CI, −12.8/−0.43), while semitendinosus (P < 0.05, d = −0.79; 95% CI, 0.62/20.59) electromyographic activity was greater in the back squat during the ascending phase. Compared to the front squat version, back squat exhibited significantly greater trunk lean, with no differences occurring in the knee joint kinematics throughout the movement. Results may suggest that the front squat may be preferred to the back squat for knee extensor development and for preventing possible lumbar injuries during maximum loading.