The Duration of Non-Local Muscle Fatigue Effects.

Non-local muscle fatigue (NLMF) refers to a transient decline in the functioning of a non-exercised muscle following the fatigue of a different muscle group. Most studies examining NLMF conducted post-tests immediately after the fatiguing protocols, leaving the duration of these effects uncertain. The aim of this study was to investigate the duration of NLMF (1-, 3-, and 5-minutes). In this randomized crossover study, 17 recreationally trained participants (four females) were tested for the acute effects of unilateral knee extensor (KE) muscle fatigue on the contralateral homologous muscle strength, and activation. Each of the four sessions included testing at either 1-, 3-, or 5-minutes post-test, as well as a control condition for non-dominant KE peak force, instantaneous strength (force produced within the first 100-ms), and vastus lateralis and biceps femoris electromyography (EMG). The dominant KE fatigue intervention protocol involved two sets of 100-seconds maximal voluntary isometric contractions (MVIC) separated by 1-minute of rest. Non-dominant KE MVIC forces showed moderate and small magnitude reductions at 1-min (p < 0.0001, d = 0.72) and 3-min (p = 0.005, d = 0.30) post-test respectively. The KE MVIC instantaneous strength revealed large magnitude, significant reductions between 1-min (p = 0.021, d = 1.33), and 3-min (p = 0.041, d = 1.13) compared with the control. In addition, EMG data revealed large magnitude increases with the 1-minute versus control condition (p = 0.03, d = 1.10). In summary, impairments of the non-exercised leg were apparent up to 3-minutes post-exercise with no significant deficits at 5-minutes. Recovery duration plays a crucial role in the manifestation of NLMF.

Thoracolumbar Fascia and Lumbar Muscle Stiffness in Athletes with A History of Hamstring Injury.

The purpose of this study was to examine the differences in thoracolumbar fascia (TLF) and lumbar muscle modulus in individuals with and without hamstring injury using shear wave elastography (SWE). Thirteen male soccer players without a previous hamstring injury and eleven players with a history of hamstring injury performed passive and active (submaximal) knee flexion efforts from 0°, 45° and 90° angle of knee flexion as well as an active prone trunk extension test. The elastic modulus of the TLF, the erector spinae (ES) and the multifidus (MF) was measured using ultrasound SWE simultaneously with the surface electromyography (EMG) signal of the ES and MF. The TLF SWE modulus was significantly (p < 0.05) higher in the injured group (range: 29.86 ± 8.58 to 66.57 ± 11.71 kPa) than in the uninjured group (range: 17.47 ± 9.37 to 47.03 ± 16.04 kPa). The ES and MF modulus ranged from 14.97 ± 4.10 to 66.57 ± 11.71 kPa in the injured group and it was significantly (p < .05) greater compared to the uninjured group (range: 11.65 ± 5.99 to 40.49 ± 12.35 kPa). TLF modulus was greater than ES and MF modulus (p < 0.05). Active modulus was greater during the prone trunk extension test compared to the knee flexion tests and it was greater in the knee flexion test at 0° than at 90° (p < 0.05). The muscle EMG was greater in the injured compared to the uninjured group in the passive tests only (p < 0.05). SWE modulus of the TLF and ES and MF was greater in soccer players with previous hamstring injury than uninjured players. Further research could establish whether exercises that target the paraspinal muscles and the lumbar fascia can assist in preventing individuals with a history of hamstring injury from sustaining a new injury.

Do athletes with hamstring strain injury have shorter muscle fascicles in the injured limb?

INTRODUCTION: Previous studies have suggested that a reduced length of the biceps femoris long head (BFlh) fascicles may increase the risk of hamstring strain injury (HSI). However, it remains unclear whether the BFlh fascicles of the injured limb are shorter than those of the contralateral limb in athletes with an acute HSI. OBJECTIVE: To investigate the between-limb asymmetry of BFlh fascicle length in amateur athletes with an acute HSI. METHODS: Male amateur athletes were evaluated using ultrasound scans within five days following an HSI. The BFlh fascicle length was estimated using a validated equation. RESULTS: Eighteen injured athletes participated in this study. There was no significant difference (p = 0.27) in the length of BFlh fascicles between the injured limb (9.53 ± 2.55 cm; 95%CI 8.26 to 10.80 cm) and the uninjured limb (10.54 ± 2.87 cm; 95%CI 9.11 to 11.97 cm). Individual analysis revealed high heterogeneity, with between-limb asymmetries (percentage difference of the injured limb compared to the uninjured limb) ranging from -42% to 25%. Nine out of the 18 athletes had a fascicle length that was more than 10% shorter in the injured limb compared to the uninjured limb, five athletes had a difference of less than 10%, and four athletes had a fascicle length that was more than 10% longer in the injured limb compared to the uninjured limb. CONCLUSION: The architecture characteristics of injured and uninjured muscles is not consistent among athletes with HSI. Therefore, rehabilitation programs focused on fascicle lengthening should be evaluated on a case-by-case basis.

Effect of Eutony, Holistic Gymnastics and Pilates on hamstring flexibility and back pain in pre-adolescent girls: Randomized clinical trial.

OBJECTIVE: This study aimed to evaluate the effects of Eutony, Holistic Gymnastics, and Pilates on hamstring flexibility and back pain in pre-adolescent girls. METHODS: This randomized prospective quantitative clinical trial compared the effects of Eutony, Holistic Gymnastics, and Pilates on hamstring flexibility and back pain. The sample consisted of 80 pre-adolescent girls aged 10-13 years and divided into three groups: Eutony, with 26 girls; Holistic Gymnastics, 27 girls; and Pilates, 27 girls. The participants underwent ten 1-h weekly interventions. Hamstring flexibility was evaluated using fingertip-to-floor, sit-and-reach, and hip angle tests; back pain was evaluated using the Body Posture Evaluation Instrument questionnaire and the way they carried their backpack by the Layout for Assessing Dynamic Posture. Descriptive statistical analysis, analysis of variance, and Kruskal-Wallis test were performed at a 5 % significance level (p < 0.05). RESULTS: The three body practices increased hamstring flexibility in all fingertip-to-floor (7.77 cm), hip angle (5.58°), and sit-and-reach evaluations (9.07 cm). Before the intervention, 66.25 % of participants complained of back pain. After the intervention, only 37.50 % continued with the complaint. Moreover, 25 % of pre-adolescent girls started to carry their school backpack correctly. CONCLUSION: Eutony, Holistic Gymnastics, and Pilates increased hamstring flexibility, reduced back pain complaints, and incentivized the girls to carry the school backpack correctly. REGISTRY OF CLINICAL TRIALS: Brazilian Registry of Clinical Trials ReBEC (RBR-25w6kk).

Evaluation of muscular and functional inter-limb asymmetries during mid-season in young male soccer athletes.

BACKGROUND: To identify inter-limb asymmetries through the knee's muscular and lower limb functional performance in young male soccer athletes. METHODS: Twenty male soccer athletes aged 17 to 19 from an under-20 team performed isokinetic tests at 60°/s., 120°/s., 180°/s., and 240°/s. To assess the knee extensors and flexors muscles and functional tests (hop tests and Y-balance test). RESULTS: There were no significant differences between the dominant limb (DL) and non-dominant limb (NDL) in the knee extensors and flexors peak torque and hamstrings (H)/quadriceps(Q) conventional ratio. Moreover, no angular velocities observed inter-limb asymmetries seen by values higher than 10% in the isokinetic parameters. However, the H/Q conventional ratio shows borderline values in low angular velocities (60°/s. and 120°/s.). No significant changes were observed in the functional test performance between the DL and NDL. Furthermore, we did not see inter-limb asymmetries in both hop and Y-balance tests. On the contrary, the anterior distance reached was lower than found in the literature, and the composite score of the Y-balance test demonstrated values below the normative (>94%). CONCLUSION: The data demonstrated that soccer athletes have muscular and functional inter-limb symmetry. However, they tend to have knee muscle imbalance in low velocities and dynamic balance deficits that might increase the risk of musculoskeletal injury.

Reciprocal inhibition of the thigh muscles in humans: A study using transcutaneous spinal cord stimulation.

Evaluating reciprocal inhibition of the thigh muscles is important to investigate the neural circuits of locomotor behaviors. However, measurements of reciprocal inhibition of thigh muscles using spinal reflex, such as H-reflex, have never been systematically established owing to methodological limitations. The present study aimed to clarify the existence of reciprocal inhibition in the thigh muscles using transcutaneous spinal cord stimulation (tSCS). Twenty able-bodied male individuals were enrolled. We evoked spinal reflex from the biceps femoris muscle (BF) by tSCS on the lumber posterior root. We examined whether the tSCS-evoked BF reflex was reciprocally inhibited by the following conditionings: (1) single-pulse electrical stimulation on the femoral nerve innervating the rectus femoris muscle (RF) at various inter-stimulus intervals in the resting condition; (2) voluntary contraction of the RF; and (3) vibration stimulus on the RF. The BF reflex was significantly inhibited when the conditioning electrical stimulation was delivered at 10 and 20 ms prior to tSCS, during voluntary contraction of the RF, and during vibration on the RF. These data suggested a piece of evidence of the existence of reciprocal inhibition from the RF to the BF muscle in humans and highlighted the utility of methods for evaluating reciprocal inhibition of the thigh muscles using tSCS.

Sustainable effectiveness of kinetic chain stretching on active hip flexion movement and muscle activation for hamstring tightness: A preliminary investigation.

BACKGROUND: Conventional hamstring (HAM) stretching therapeutic effects are not substantiable in neuromusculoskeletal conditions with HAM tightness or shortness. We developed a kinetic chain stabilization exercise to provide a more sustainable effectiveness in adults with HAM tightness. However, its therapeutic effects and underlying motor mechanisms remain unknown. OBJECTIVE: To compare the effects of traditional active HAM stretching (AHS) and kinetic chain stretching (KCS) on electromyographic (EMG) amplitude and hip flexion range of motion (ROM) in participants with HAM tightness. METHODS: In this randomized controlled trial, 18 participants (mean age: 25.01 ± 2.47 years) with HAM tightness were assigned to the AHS or KCS group. Hip joint movement, EMG amplitude, and onset times were recorded in the bilateral erector spinae, HAM, transverse abdominis/internal oblique (IO), external oblique (EO), and rectus abdominis during a straight leg raise test. RESULTS: Compared to AHS, KCS led to greater increase in the hip flexion ROM and EMG activation amplitudes in the left and right EO and left IO. Post-test hip flexion ROM data in both the groups were higher than the pre-test data. CONCLUSION: KCS produced more sustainable effectiveness in hip flexion movement and EMG motor control patterns in participants with HAM tightness than AHS.

Distal hamstrings tendons mechanical properties at rest and contraction using free-hand 3-D ultrasonography.

Tendon properties impact human locomotion, influencing sports performance, and injury prevention. Hamstrings play a crucial role in sprinting, particularly the biceps femoris long head (BFlh), which is prone to frequent injuries. It remains uncertain if BFlh exhibits distinct mechanical properties compared to other hamstring muscles. This study utilized free-hand three-dimensional ultrasound to assess morphological and mechanical properties of distal hamstrings tendons in 15 men. Scans were taken in prone position, with hip and knee extended, at rest and during 20%, 40%, 60%, and 80% of maximal voluntary isometric contraction of the knee flexors. Tendon length, volume, cross-sectional area (CSA), and anteroposterior (AP) and mediolateral (ML) widths were quantified at three locations. Longitudinal and transverse deformations, stiffness, strain, and stress were estimated. The ST had the greatest tendon strain and the lowest stiffness as well as the highest CSA and AP and ML width strain compared to other tendons. Biceps femoris short head (BFsh) exhibited the least strain, AP and ML deformation. Further, BFlh displayed the highest stiffness and stress, and BFsh had the lowest stress. Additionally, deformation varied by region, with the proximal site showing generally the lowest CSA strain. Distal tendon mechanical properties differed among the hamstring muscles during isometric knee flexions. In contrast to other bi-articular hamstrings, the BFlh high stiffness and stress may result in greater energy absorption by its muscle fascicles, rather than the distal tendon, during late swing in sprinting. This could partly account for the increased incidence of hamstring injuries in this muscle.

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.

Validity and Reliability of Handheld Dynamometry to Assess Isometric Hamstrings and Quadriceps Strength at Varying Muscle Lengths.

CONTEXT: The hamstrings are the most commonly injured muscle in sports and are especially injury prone in lengthened positions. Measuring knee muscle strength in such positions could be relevant to establish injury risk. Handheld dynamometry has been shown to be a valid, reliable, and practical tool to measure isometric muscle strength clinically. The aim of this study was to assess the validity and reliability of the assessment of isometric knee muscle strength with a handheld dynamometer (HHD) at various muscle lengths, by modifying the hip and knee angles during testing. DESIGN: Concurrent validity and test-retest reliability. METHODS: Thirty young healthy participants were recruited. Hamstring and quadriceps isometric strength was measured with a HHD and with an isokinetic dynamometer, over 2 testing sessions, in a randomized order. Isometric strength was measured on the right lower limb in 6 different positions, with the hip at either 0° or 80° of flexion and the knee at either 30°, 60°, or 90° of flexion. Pearson and Spearman correlations were used to assess the validity, and intraclass correlation coefficients were calculated to establish the test-retest reliability of the HHD. RESULTS: Good to excellent reliability and moderate to high validity were found in all the tested muscle length positions, except for the hamstrings in a seated position with the knee extended at 30°. CONCLUSIONS: The use of a HHD is supported in the clinical setting to measure knee muscle strength at varying muscle lengths in healthy adults, but not for the hamstrings in a lengthened position (hip flexed and knee extended). These results will have to be confirmed in sport-specific populations.

Intra- and inter-limb strength imbalance and asymmetry in soccer: A comparison of elite senior and junior players.

Evaluation of muscle strength imbalance can be an important element in optimizing the training process of soccer players. The purpose of the study was to examine isokinetic peak torque (PT) and total work (TW) exerted by both knee extensors (quadriceps or Q) and flexors (hamstrings or H), intra-limb imbalance and the magnitude and direction of inter-limb asymmetry in top elite senior (n = 109) and junior (n = 74) soccer players. An isokinetic dynamometry was used to measure maximum peak torque of quadriceps (PT-Q) and hamstrings (PT-H) at an angular velocity of 60° ·s-1, as well as the total work for extensors (TW-Q) and flexors (TW-H) at an angular velocity of 240° ·s-1 in the dominant (DL) and non-dominant leg (NDL) during concentric muscle contraction. Intra-limb imbalance and inter-limb asymmetries were calculated using a standard equation. Statistical analysis using t-test and Mann-Whitney U-test revealed: (a) no differences (p > 0.05) between groups for PT-Q and PT-H, (b) greater strength levels (p < 0.05) for TW-Q and TW-H of senior players than juniors, and (c) no differences (p > 0.05) between groups for intra-limb imbalance and inter-limb asymmetry. Additionally, Pearson's chi-kwadrat (χ2) analysis showed no differences (p > 0.05) between groups for intra-limb imbalance and inter-limb asymmetry in relation to the 'normative' values accepted in the literature that indicate an increase in the risk of knee injury. This study shows that isokinetic assessment can be an important tool to identify imbalances/asymmetries and to develop strategies to reduce the risk of muscle injury.

Combined Effects of Static and Dynamic Stretching on the Muscle-Tendon Unit Stiffness and Strength of the Hamstrings.

ABSTRACT: Takeuchi, K, Nakamura, M, Matsuo, S, Samukawa, M, Yamaguchi, T, and Mizuno, T. Combined effects of static and dynamic stretching on the muscle-tendon unit stiffness and strength of the hamstrings. J Strength Cond Res 38(4): 681-686, 2024-Combined static and dynamic stretching for 30 seconds is frequently used as a part of a warm-up program. However, a stretching method that can both decrease muscle-tendon unit (MTU) stiffness and increase muscle strength has not been developed. The purpose of this study was to examine the combined effects of 30 seconds of static stretching at different intensities (normal-intensity static stretching [NS] and high-intensity static [HS]) and dynamic stretching at different speeds (low-speed dynamic [LD] and high-speed dynamic stretching [HD]) on the MTU stiffness and muscle strength of the hamstrings. Thirteen healthy subjects (9 men and 4 women, 20.9 ± 0.8 years, 169.3 ± 7.2 cm, 61.1 ± 8.2 kg) performed 4 types of interventions (HS-HD, HS-LD, NS-HD, and NS-LD). Range of motion (ROM), passive torque, MTU stiffness, and muscle strength were measured before and immediately after interventions by using an isokinetic dynamometer machine. In all interventions, the ROM and passive torque significantly increased (p < 0.01). Muscle-tendon unit stiffness significantly decreased in HS-HD and HS-LD (both p < 0.01), but there was no significant change in NS-HD (p = 0.30) or NS-LD (p = 0.42). Muscle strength significantly increased after HS-HD (p = 0.02) and NS-LD (p = 0.03), but there was no significant change in HS-LD (p = 0.23) or NS-LD (p = 0.26). The results indicated that using a combination of 30 seconds of high-intensity static stretching and high-speed dynamic stretching can be beneficial for the MTU stiffness and muscle strength of the hamstrings.

The Sprint Mechanics Assessment Score: A Qualitative Screening Tool for the In-field Assessment of Sprint Running Mechanics.

BACKGROUND: Qualitative movement screening tools provide a practical method of assessing mechanical patterns associated with potential injury development. Biomechanics play a role in hamstring strain injury and are recommended as a consideration within injury screening and rehabilitation programs. However, no methods are available for the in-field assessment of sprint running mechanics associated with hamstring strain injuries. PURPOSE: To investigate the intra- and interrater reliability of a novel screening tool assessing in-field sprint running mechanics titled the Sprint Mechanics Assessment Score (S-MAS) and present normative S-MAS data to facilitate the interpretation of performance standards for future assessment uses. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 3. METHODS: Maximal sprint running trials (35 m) were recorded from 136 elite soccer players using a slow-motion camera. All videos were scored using the S-MAS by a single assessor. Videos from 36 players (18 men and 18 women) were rated by 2 independent assessors blinded to each other's results to establish interrater reliability. One assessor scored all videos in a randomized order 1 week later to establish intrarater reliability. Intraclass correlation coefficients (ICCs) based on single measures using a 2-way mixed-effects model, with absolute agreement with 95% CI and kappa coefficients with percentage agreements, were used to assess the reliability of the overall score and individual score items, respectively. T-scores were calculated from the means and standard deviations of the male and female groups to present normative data values. The Mann-Whitney U test and the Wilcoxon signed-rank test were used to assess between-sex differences and between-limb differences, respectively. RESULTS: The S-MAS showed good intrarater (ICC, 0.828 [95% CI, 0.688-0.908]) and interrater (ICC, 0.799 [95% CI, 0.642-0.892]) reliability, with a standard error of measurement of 1 point. Kappa coefficients for individual score items demonstrated moderate to substantial intra- and interrater agreement for most parameters, with percentage agreements ranging from 75% to 88.8% for intrarater and 66.6% to 88.8% for interrater reliability. No significant sex differences were observed for overall scores, with mean values of 4.2 and 3.8 for men and women, respectively (P = .27). CONCLUSION: The S-MAS is a new tool developed for assessing sprint running mechanics associated with lower limb injuries in male and female soccer players. The reliable and easy-to-use nature of the S-MAS means that this method can be integrated into practice, potentially aiding future injury screening and research looking to identify athletes who may demonstrate mechanical patterns potentially associated with hamstring strain injuries.

Investigating balance-related gait patterns and their relationship with maximum torques generated by the hamstrings and quadriceps in older adults - Results from the Baltimore longitudinal study of aging.

BACKGROUND: Balance-related gait patterns in older adults can be objectively discerned through the examination of gait parameters, maximum leg torques, and their interconnections. OBJECTIVE: To investigate the correlation between leg muscle strength and balance during gait concerning functional performance in healthy older adults. METHODS: Participants included 117 adults aged 60-95 years were recruited from the Baltimore Longitudinal Study of Aging (BLSA). They underwent evaluations of gait, balance, and maximum isometric leg torque (for both hamstrings and quadriceps). Analyses examined the association between leg torque and functional performance among those with higher and lower balances. RESULTS: Individuals with lower balance (n = 43) were older, more prone to experiencing a fear of falling, and exhibited lower functional performance (gait speeds and Generalized Gait Stability Scores (GGSS), ps < 0.001) compared to their counterparts with higher balance (n = 74). At a usual walking pace, the GGSS showed a positive association with concentric Quadriceps Maximum Torque (QMT) in participants with lower balance (p = 0.013). Conversely, it displayed a positive association with eccentric QMT in those with higher balance (p = 0.014). At a fast walking pace, only individuals with higher balance demonstrated a positive muscle torque association with both gait speed and GGSS, encompassing concentric and eccentric actions in both the quadriceps and hamstrings (ps < 0.050). CONCLUSION: Evaluating muscle strength capacity in both concentric and eccentric phases during dynamic high-effort events, along with investigating their associations with gait performance, can be beneficial for identifying subtle gait deficits. This comprehensive approach may assist in the early detection of gait deterioration among healthy older adults, given the intricate muscle activations involved in lower body functional performance.

Longer Ground Contact Time Is Related to a Superior Running Economy in Highly Trained Distance Runners.

ABSTRACT: Tanji, F, Ohnuma, H, Ando, R, Yamanaka, R, Ikeda, T, and Suzuki, Y. Longer ground contact time is related to a superior running economy in highly trained distance runners. J Strength Cond Res 38(5): 985-990, 2024-Running economy is a key component of distance running performance and is associated with gait parameters. However, there is no consensus of the link between the running economy (RE), ground contact time, and footstrike patterns. Thus, this study aimed to clarify the relationship between RE, ground contact time, and thigh muscle cross-sectional area (CSA) in highly trained distance runners and to compare these parameters between 2 habitual footstrike patterns (midfoot vs. rearfoot). Seventeen male distance runners ran on a treadmill to measure RE and gait parameters. We collected the CSAs of the right thigh muscle using a magnetic resonance imaging scanner. The RE had a significant negative relationship with distance running performance ( r = -0.50) and ground contact time ( r = -0.51). The ground contact time had a significant negative relationship with the normalized CSAs of the vastus lateralis muscle ( r = -0.60) and hamstrings ( r = -0.54). No significant differences were found in RE, ground contact time, or normalized CSAs of muscles between midfoot ( n = 10) and rearfoot ( n = 7) strikers. These results suggest that large CSAs of knee extensor muscles results in short ground contact time and worse RE. The effects of the footstrike pattern on the RE appear insignificant, and the preferred footstrike pattern can be recommended for running in highly trained runners.

Effect of Hindlimb Unloading on Hamstring Muscle Activity in Rats.

INTRODUCTION: The changes in knee axial rotation play an important role in traumatic and non-traumatic knee disorders. It is known that support afferentation can affect the axial rotator muscles. The condition of innervation of the semitendinosus (ST) and biceps femoris posterior (BFp) has changed in non-terrestrial and terrestrial vertebrates in evolution; thus, we hypothesized this situation might be replayed by hindlimb unloading (HU). METHODS: In the present study, the EMG activity of two hamstring muscles, m. ST and m. BFp, which are antagonists in axial rotation of the tibia, was examined before and after 7 days of HU. RESULTS: During locomotion and swimming, the ST flexor burst activity increased in the stance-to-swing transition and in the retraction-protraction transition, respectively, while that of BFp remained unchanged. Both ST and BFp non-burst extensor activity increased during stepping and decreased during swimming. CONCLUSIONS: Our results show that (1) the flexor burst activity of ST and BFp depends differently on the load-dependent sensory input in the step cycle; (2) shift of the activity gradient towards ST in the stance-to-swing transition could produce excessive internal tibia torque, which can be used as an experimental model of non-traumatic musculoskeletal disorders; and (3) the mechanisms of activity of ST and BFp may be based on reciprocal activity of homologous muscles in primary tetrapodomorph and depend on the increased role of supraspinal control.

Moment arm and torque generating capacity of semitendinosus following tendon harvesting for anterior cruciate ligament reconstruction: A simulation study.

Altered semitendinosus (ST) morphology and distal tendon insertion following anterior cruciate ligament reconstruction (ACLR) may reduce knee flexion torque generating capacity of the hamstrings via impaired ST force generation and/or moment arm. This study used a computational musculoskeletal model to simulate mechanical consequences of tendon harvest for ACLR on ST function by modeling changes in ST muscle tendon insertion point, moment arm, and torque generating capacity across a physiological range of motion. Simulated ST function was then compared between ACLR and uninjured contralateral limbs. Magnetic resonance imaging from 18 individuals with unilateral history of ACLR involving a hamstring autograft was used to analyse bilateral hamstring muscle (ST, semimembranosus, bicep femoris long head and short head) morphology and distal ST tendon insertion. The ACLR cohort was sub-grouped into those with and without ST regeneration. For each participant with ST regeneration (n = 7), a personalized musculoskeletal model was created including postoperative remodeling of ST using OpenSim 4.1. Knee flexion and internal rotation moment arms and torque generating capacities of hamstrings were evaluated. Bilateral differences were calculated with an asymmetry index (%) ([unaffected limb-affected limb]/[unaffected limb + affected limb]*100%). Smaller moment arms or knee torques within injured compared to uninjured contralateral limbs were considered a deficit. Compared to uninjured contralateral limbs, ACLR limbs with tendon regeneration (n = 7) had minor reductions in knee flexion (5.80% [95% confidence interval (CI) = 3.97-7.62]) and internal rotation (4.92% [95% CI = 2.77-7.07]) moment arms. Decoupled from muscle morphology, altered ST moment arms in ACLR limbs with tendon regeneration resulted in negligible deficits in knee flexion (1.20% [95% CI = 0.34-2.06]) and internal rotation (0.24% [95% CI = 0.22-0.26]) torque generating capacity compared to uninjured contralateral limbs. Coupled with muscle morphology, ACLR limbs with tendon regeneration had substantial deficits in knee flexion (19.32% [95% CI = 18.35-20.28]) and internal rotation (15.49% [95% CI = 14.56-16.41]) torques compared to uninjured contralateral limbs. Personalized musculoskeletal models with measures of ST distal insertion and muscle morphology provided unique insights into post-ACLR ST and hamstring function. Deficits in knee flexor and internal rotation moment arms and torque generating capacities were evident in those with ACLR even when tendon regeneration occurred. Future studies may wish to implement this framework in personalized musculoskeletal models following ACLR to better understand individual muscle function for injury prevention and treatment evaluation.

The effects of eccentric training on hamstring flexibility and strength in young dance students.

The objective of this research is to examine the impact of eccentric training on hamstring flexibility and strength in young dancers during the concluding stages of their foundational dance training program. A total of 24 female, second-year dance students from Hebei Normal University were selected as participants. They were divided into three distinct groups: Nordic hamstring exercise and single-leg deadlift group (NHE&SLD), forward bending exercises and standing leg lift group (FBE&SLL), and a control group (CG). The study was designed around a 6-week training regimen. An isokinetic dynamometer was used to measure seated knee flexor-extensor strength, while electronic goniometry was employed to measure hamstring flexibility in the supine position. Paired sample t-tests were conducted within each group, and one-way analysis of covariance (ANCOVA) was utilized for comparisons between groups. In the NHE&SLD group, significant disparities were observed in both concentric (T = - 5.687, P = 0.001) and eccentric (T = - 3.626, P = 0.008) hamstring strength pre and post-intervention. The pre-intervention dominant leg concentric strength test values significantly influenced the post-intervention outcomes (F = 5.313, P = 0.001, η2 = 0.840). Similarly, the pre-intervention dominant leg eccentric strength test values impacted the post-intervention results (F = 4.689, P = 0.043, η2 = 0.190). Following the intervention, the NHE&SLD group displayed marked changes in the active straight leg raising angle on both left (T = - 4.171, P = 0.004) and right (T = - 6.328, P = 0.001) sides. The FBE&SLL group also revealed significant changes in the active straight leg raising angle on both left (T = - 4.506, P = 0.003) and right (T = - 4.633, P = 0.002) sides following the intervention. The pre-intervention left leg concentric strength test value significantly influenced the post-intervention outcomes (F = 25.067, P = 0.001, η2 = 0.556). Likewise, the pre-intervention right leg eccentric strength test value significantly influenced the post-intervention results (F = 85.338, P = 0.01, η2 = 0.810). Eccentric training can better enhance the flexibility and strength of hamstring muscles in dance students. Traditional stretching training significantly improves the flexibility of the hamstring muscles. Eccentric training has more training benefits than traditional stretching training. It is recommended for dance students to use eccentric training when increasing hamstring flexibility and strength.

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

INTRODUCTION: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.

Progressive submaximal effort hamstring muscle endurance is reduced after reconstruction of the anterior cruciate ligament.

BACKGROUND: Endurance capability in the muscles controlling the knee is poorly understood post anterior cruciate ligament (ACL) reconstruction, despite many sporting activities requiring notable muscle endurance. The hamstring muscles, when active, provide important anatomical support to protect the reconstructed graft. In the absence of good hamstring endurance, fatigue may predispose individuals to re-injury. OBJECTIVE: To assess whether ACL reconstruction (ACLR) with a hamstring graft leads to reduced hamstring endurance 9-13 months post-surgery. STUDY DESIGN: A cross-sectional inter-limb comparison study was undertaken with participants 9-13 months after an ACLR with a hamstring graft, and a group of age, sex, and activity-matched controls. There were 22 participants in each group. METHOD: Submaximal hamstring endurance was measured using a progressive fatigue test on an isokinetic dynamometer at a joint angular velocity of 120°/second. The dependant variable was the maximum number of repetitions performed. Statistical comparisons were made across injured, uninjured and control group limbs. RESULTS: There was a significant (p < 0.05) deficit in hamstring endurance observed between the injured leg (mean: 111 repetitions, SD 49) and uninjured leg (mean: 136 repetitions, SD 67) of the ACL group, but not between the uninjured and control group legs (mean: 124 repetitions, SD 50). CONCLUSION: The 18% deficit in submaximal hamstring endurance across the ACL-reconstructed individual's limbs is indicative of a notable loss in muscle performance at 9-13 months post-surgery. These results provide initial evidence for supporting further research examining the inclusion of hamstring endurance training in ACL rehabilitation programmes post-surgery.