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BackgroundThe architectural and morphological adaptations of the hamstrings in response to training with different exercises have not been explored.PurposeTo 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.Methods30 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.ResultsCompared 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).ConclusionNHE and HE training both stimulate significant increases in BFLH fascicle length; however, HE training may be more effective for promoting hypertrophy in the BFLH.

The 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. In 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). For 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. The 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.

Purpose Hamstring strain injury is a frequent and serious injury in competitive and recreational sports. While Nordic hamstring (NH) eccentric strength training is an effective hamstring injury-prevention method, the protective mechanism of this exercise is not understood. Strength training increases muscle strength, but also alters muscle architecture and stiffness; all three factors may be associated with reducing muscle injuries. The purpose of this study was to examine the effects of NH eccentric strength training on hamstring muscle architecture, stiffness, and strength. Methods Twenty healthy participants were randomly assigned to an eccentric training group or control group. Control participants performed static stretching, while experimental participants performed static stretching and NH training for 6 weeks. Pre- and post-intervention measurements included: hamstring muscle architecture and stiffness using ultrasound imaging and elastography, and maximal hamstring strength measured on a dynamometer. Results The experimental group, but not the control group, increased volume (131.5 vs. 145.2 cm 3 , p  < 0.001) and physiological cross-sectional area (16.1 vs. 18.1 cm 2 , p  = 0.032). There were no significant changes to muscle fascicle length, stiffness, or eccentric hamstring strength. Conclusions The NH intervention was an effective training method for muscle hypertrophy, but, contrary to common literature findings for other modes of eccentric training, did not increase fascicle length. The data suggest that the mechanism behind NH eccentric strength training mitigating hamstring injury risk could be increasing volume rather than increasing muscle length. Future research is, therefore, warranted to determine if muscle hypertrophy induced by NH training lowers future hamstring strain injury risk.

This study investigated the effect of five consecutive days of cold‐water immersion (CWI) on recovery from exercise‐induced muscle damage (EIMD) in the hamstrings following maximal eccentric contraction (EC) exercise. Eighteen healthy adult women were randomly assigned to a CWI group and a control group (CG) (n = 9/group). Participants performed 10 sets of 10 repetitions of isokinetic EC at 30°/second and underwent maximum voluntary isometric contraction (MVC), delayed onset muscle soreness (DOMS) assessment, straight leg raise (SLR) test, and plasma myoglobin (Mb) measurement. The CWI group received one 14‐min session of CWI treatment (14°C) at 1, 25, 49, 73, and 97 h after the EC test, whereas the CG rested in a seated position at the same five time points without receiving treatment. (1) All the dependent variables in the CWI group and CG exhibited significant changes after the EC test (p < 0.05). (2) The recovery effect in the CWI group was significantly greater than in the CG in terms of the MVC, DOMS, SLR, and plasma Mb concentration results. MVC increased by 89.3 ± 2.0% on the fourth day (p < 0.013), DOMS decreased by 15.4 ± 1.5 mm on the second day (p < 0.000), SLR increased by 86.3 ± 1.1% on the second day (p < 0.014), and plasma Mb decreased by 436.3 ± 60.8% on the third day (p < 0.014). The study indicates that five consecutive days of CWI at 14°C significantly enhance recovery from exercise‐induced muscle damage in the hamstrings. Highlights CWI treatment was beneficial for recovery from EIMD after high‐intensity exercise. All the participants exhibited similar and significant responses in their MVC, DOMS, SLR, and plasma Mb concentration results after the EC test. The CWI group demonstrated mostly superior recovery responses compared with the CG after receiving the CWI treatment on 5 consecutive days after the EC test.

Anterior cruciate ligament (ACL) injuries impact approximately 68.6 per 100,000 individuals annually, with ACL reconstruction (ACLR) being a common intervention for restoring knee stability in physically active individuals. Despite advancements in surgical techniques and rehabilitation protocols, patients often experience prolonged recovery, hamstring weakness, and neuromuscular deficits, increasing the risk of re-injury and osteoarthritis. Early-phase ACLR rehabilitation primarily focuses on managing pain, swelling, and quadriceps strength, frequently neglecting the critical role of hamstrings in knee stabilization. This leaves a gap in addressing imbalances that hinder functional recovery and return-to-sport timelines. Upper limb isometric training (ULIT) presents an innovative approach to enhance hamstring activation during the early rehabilitation phase. By leveraging the posterior myofascial kinetic chain (PMKC), ULIT indirectly stimulates hamstrings through bilateral static upper limb exercises, such as wall push up, shoulder extension and scapular retraction, promoting neuromuscular coordination and kinetic chain synergy. These exercises mitigate challenges associated with direct hamstring loading, such as arthrogenic muscle inhibition and graft protection needs. Preliminary research suggests upper limb resistance exercise at submaximal voluntary contraction facilitates inter-limb strength gains, improves core abdominals and hamstring activation, and reduces knee imbalances, supporting accelerated recovery and reduced re-injury risk. The ULIT demonstrates potential as an alternative warm-up exercise to promote hamstring activation and enhance overall readiness for physical activity. Emerging findings highlight ULIT as a safe and potentially effective supplementary intervention, but further research is essential to establish its role in ACLR rehabilitation and develop evidence-based protocols. This study aims to evaluate the effects of integrating ULIT into standard care rehabilitation on hamstring strength and physical function in early-phase postoperative ACLR patients with hamstring autograft. The findings could introduce a novel and effective strategy to optimize recovery, enhance functional outcomes, and support a safer return to sport. Trial registration number: ACTRN12624001445561 and available at https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=388441&isReview=true .

Background We implemented a blood flow restriction resistance training (BFR-RT) intervention during an 8-week rehabilitation programme in anterior cruciate ligament reconstruction (ACLR) patients within a National Health Service setting. Objective To compare the effectiveness of BFR-RT and standard-care traditional heavy-load resistance training (HL-RT) at improving skeletal muscle hypertrophy and strength, physical function, pain and effusion in ACLR patients following surgery. Methods 28 patients scheduled for unilateral ACLR surgery with hamstring autograft were recruited for this parallel-group, two-arm, single-assessor blinded, randomised clinical trial following appropriate power analysis. Following surgery, a criteria-driven approach to rehabilitation was utilised and participants were block randomised to either HL-RT at 70% repetition maximum (1RM) ( n  = 14) or BFR-RT ( n  = 14) at 30% 1RM. Participants completed 8 weeks of biweekly unilateral leg press training on both limbs, totalling 16 sessions, alongside standard hospital rehabilitation. Resistance exercise protocols were designed consistent with standard recommended protocols for each type of exercise. Scaled maximal isotonic strength (10RM), muscle morphology of the vastus lateralis of the injured limb, self-reported function, Y-balance test performance and knee joint pain, effusion and range of motion (ROM) were assessed at pre-surgery, post-surgery, mid-training and post-training. Knee joint laxity and scaled maximal isokinetic knee extension and flexion strength at 60°/s, 150°/s and 300°/s were measured at pre-surgery and post-training. Results Four participants were lost, with 24 participants completing the study (12 per group). There were no adverse events or differences between groups for any baseline anthropometric variable or pre- to post-surgery change in any outcome measure. Scaled 10RM strength significantly increased in the injured limb (104 ± 30% and 106 ± 43%) and non-injured limb (33 ± 13% and 39 ± 17%) with BFR-RT and HL-RT, respectively, with no group differences. Significant increases in knee extension and flexion peak torque were observed at all speeds in the non-injured limb with no group differences. Significantly greater attenuation of knee extensor peak torque loss at 150°/s and 300°/s and knee flexor torque loss at all speeds was observed with BFR-RT. No group differences in knee extensor peak torque loss were found at 60°/s. Significant and comparable increases in muscle thickness (5.8 ± 0.2% and 6.7 ± 0.3%) and pennation angle (4.1 ± 0.3% and 3.4 ± 0.1%) were observed with BFR-RT and HL-RT, respectively, with no group differences. No significant changes in fascicle length were observed. Significantly greater and clinically important increases in several measures of self-reported function (50–218 ± 48% vs. 35–152 ± 56%), Y-balance performance (18–59 ± 22% vs. 18–33 ± 19%), ROM (78 ± 22% vs. 48 ± 13%) and reductions in knee joint pain (67 ± 15% vs. 39 ± 12%) and effusion (6 ± 2% vs. 2 ± 2%) were observed with BFR-RT compared to HL-RT, respectively. Conclusion BFR-RT can improve skeletal muscle hypertrophy and strength to a similar extent to HL-RT with a greater reduction in knee joint pain and effusion, leading to greater overall improvements in physical function. Therefore, BFR-RT may be more appropriate for early rehabilitation in ACLR patient populations within the National Health Service.

PurposeThe purpose of this study was to compare the effects of squat training with different depths on lower limb muscle volumes.MethodsSeventeen males were randomly assigned to a full squat training group (FST, n = 8) or half squat training group (HST, n = 9). They completed 10 weeks (2 days per week) of squat training. The muscle volumes (by magnetic resonance imaging) of the knee extensor, hamstring, adductor, and gluteus maximus muscles and the one repetition maximum (1RM) of full and half squats were measured before and after training.ResultsThe relative increase in 1RM of full squat was significantly greater in FST (31.8 ± 14.9%) than in HST (11.3 ± 8.6%) (p = 0.003), whereas there was no difference in the relative increase in 1RM of half squat between FST (24.2 ± 7.1%) and HST (32.0 ± 12.1%) (p = 0.132). The volumes of knee extensor muscles significantly increased by 4.9 ± 2.6% in FST (p < 0.001) and 4.6 ± 3.1% in HST (p = 0.003), whereas that of rectus femoris and hamstring muscles did not change in either group. The volumes of adductor and gluteus maximus muscles significantly increased in FST (6.2 ± 2.6% and 6.7 ± 3.5%) and HST (2.7 ± 3.1% and 2.2 ± 2.6%). In addition, relative increases in adductor (p = 0.026) and gluteus maximus (p = 0.008) muscle volumes were significantly greater in FST than in HST.ConclusionThe results suggest that full squat training is more effective for developing the lower limb muscles excluding the rectus femoris and hamstring muscles.

The present study examined site-specific hamstring muscles use with functional magnetic resonance imaging (MRI) in elite soccer players during strength training. Thirty-six players were randomized into four groups, each performing either Nordic hamstring, flywheel leg-curl, Russian belt or the hip-extension conic-pulley exercise. The transverse relaxation time (T2) shift from pre- to post-MRI were calculated for the biceps femoris long (BFl) and short (BFs) heads, semitendinosus (ST) and semimembranosus (SM) muscles at proximal, middle and distal areas of the muscle length. T2 values increased substantially after flywheel leg-curl in all regions of the BFl (from 9±8 to 16±8%), BFs (41±6-71±11%), and ST (60±1-69±7%). Nordic hamstring induced a substantial T2 increase in all regions of the BFs (13±8-16±5%) and ST (15±7-17±5%). T2 values after the Russian belt deadlift substantially increased in all regions of the BFl (6±4-7±5%), ST (8±3-11±2%), SM (6±4-10±4%), and proximal and distal regions of BFs (6±6-8±5%). T2 values substantially increased after hip-extension conic-pulley only in proximal and middle regions of BFl (11±5-7±5%) and ST (7±3-12±4%). The relevance of such MRI-based inter- and intra-muscle use in designing more effective resistance training for improving hamstring function and preventing hamstring injuries in elite soccer players should be explored with more mechanistic studies.

Low back pain is a prevalent musculoskeletal disorder and affects approximately 70% of the adults in the world. To explore how balance and hamstring training improve individuals with nonspecific lower back pain (NSLBP). A total of 26 NSLBP people were randomly allocated into either the experimental group (EG) ( n  = 13) or the control group (CG) ( n  = 13). The EG was given balance and hamstring training for 45 min, 3 times per week, for up to 6 weeks, while the CG maintained daily life without any intervention. The primary outcome, the Visual Analog Scale for pain intensity, and the secondary outcomes, including the TOGU balance test for balance ability, hamstring and lumbar muscle strength and endurance, and the sit-and-reach test for hamstring flexibility, were assessed at baseline and after 6 weeks of training. For the primary outcome, the EG significantly improved pain intensity ( p  < 0.001) compared with CG. For secondary outcomes, the EG showed significant improvements in back strength ( p  = 0.015), abdominal endurance ( p  = 0.032), back endurance ( p  = 0.027), and hamstring strength ( p  = 0.007 left) ( p  = 0.005 right) following 6 weeks of training compared with the CG. However, the two groups had no significant difference in balance ability, abdominal strength, and hamstring extensibility ( p  ≥ 0.05). Six weeks of balance and hamstring training effectively reduces pain intensity and improves back strength, abdominal and back endurance, and hamstring strength. Trial registration International Standard Registered Clinical/Social Study Number (ISRCTN) registry, ISRCTN14488937 (28/05/2024).

To determine the effects of an eccentric hamstrings strength-training program, performed for at least 4 weeks by healthy adults, on muscle architecture and eccentric strength. A systematic search was performed up to October 2018 in the following electronic databases: PubMed, PEDro, CINAHL and SPORTDiscus. Combinations of the following search terms were used: , , , , , , , , , , and . Included articles were randomized controlled trials that allowed comparisons between isolated eccentric strength training of the biceps femoris muscle and other programs. Data from the included studies were extracted by 2 independent reviewers. These data included the study design, participant characteristics, inclusion and exclusion criteria of clinical studies, exercise and intervention characteristics, outcome measures, and the main results of the study. When meta-analysis was possible, we performed quantitative analysis. Ten randomized controlled trials were included. Limited to moderate evidence indicated that eccentric strength training was associated with an increase in fascicle length (mean difference [MD] = 1.97; 95% confidence interval [CI] = 1.48, 2.46), an increase in muscle thickness (MD = 0.10; 95% CI = 0.06, 0.13), and a decrease in pennation angle (MD = 2.36; 95% CI = 1.61, 3.11). Conflicted to moderate evidence indicated that eccentric hamstrings strength was increased after eccentric strength training compared with concentric strength training (standardized mean difference [SMD] = 1.06; 95% CI = 0.26, 1.86), usual level of activity (SMD = 2.72; 95% CI = 1.68, 3.77), and static stretching (SMD = 0.39; 95% CI = -0.97, 1.75). In healthy adults, an eccentric strength-training program produced architectural adaptations on the long head of the biceps femoris muscle and increased eccentric hamstrings strength.