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.

Knee and ankle range of motion and spasticity from childhood into adulthood: a longitudinal cohort study of 3,223 individuals with cerebral palsy.

BACKGROUND AND PURPOSE: Reduced range of motion (ROM) and spasticity are common secondary findings in cerebral palsy (CP) affecting gait, positioning, and everyday functioning. These impairments can change over time and lead to various needs for intervention. The aim of this study was to analyze the development path of the changes in hamstring length, knee extension, ankle dorsiflexion, and spasticity in hamstrings and gastrosoleus from childhood into adulthood in individuals with CP at the Gross Motor Function Classification System (GMFCS) levels I-V. METHODS: A longitudinal cohort study was undertaken of 61,800 measurements in 3,223 individuals with CP, born 1990-2017 and followed for an average of 8.7 years (range 0-26). The age at examination varied between 0 and 30 years. The GMFCS levels I-V, goniometric measurements, and the modified Ashworth scale (MAS) were used for repeated assessments of motor function, ROM, and spasticity. RESULTS: Throughout the follow-up period, knee extension and hamstring length exhibited a consistent decline across all individuals, with more pronounced decreases evident in those classified at GMFCS levels III-V. Ankle dorsiflexion demonstrated a gradual reduction from 15° to 5° (GMFCS I-IV) or 10° (GMFCS V). Spasticity levels in the hamstrings and gastrosoleus peaked between ages 5 and 7, showing a propensity to increase with higher GMFCS levels. CONCLUSION: Passive ROM continues to decrease to 30 years of age, most pronouncedly for knee extension. Conversely, spasticity reached its peak at a younger age, with a more notable occurrence observed in the gastrosoleus compared with the hamstrings. Less than 50% of individuals had spasticity corresponding to MAS 2-4 at any age.

Assessing muscle energy technique and foam roller self-myofascial release for low back pain management in two-wheeler riders.

Pain in the lower back is a major concern in today's era due to prolonged sitting in two-wheeler riders, mainly due to hamstring tightness. It also creates physical disability and impairment in activities of daily living. The study aimed to compare the efficacy of muscle energy technique (MET) and self-myofascial release (SMFR) using the foam roller on hamstring flexibility, dynamic balance, and physical disability amongst two-wheeler riders with chronic low back pain (LBP). Participants were randomized into two intervention groups, MET and SMFR using the envelope method, with each group having 20 participants. Hamstring flexibility and range of motion for knee extension and the lower back were assessed using the active knee extension test (AKE-L and AKE-R) and sit and reach test (SRT), while the dynamic balance was assessed by the star excursion balance test (SEBT) and physical disability by Roland-Morris Disability Questionnaire, (RMDQ). Measurements were taken at baseline and after 4 weeks of intervention. This study demonstrated that both SMFR using a foam roller and MET are effective in enhancing hamstring muscle flexibility, (SRT-F(1, 38) = 299.5, p < 0.001; AKE-R-F(1, 38) = 99.53, p < 0.001; AKE-L-F(1, 38) = 89.67, p < 0.001). Additionally, these techniques significantly improved dynamic balance in various directions, including anterior (ANT), anteromedial (AMED), medial (MED), posteromedial (PMED), posterior (POST), posterolateral (PLAT), lateral (LAT), and anterolateral (ALAT) directions (p < 0.01). Furthermore, there was a significant reduction in physical disability (RMDQ-F(1, 38) = 1307, p < 0.001), among two-wheeler riders suffering from chronic LBP. Compared to MET, SMFR using foam rollers was found to be more effective in enhancing hamstring flexibility, improving balance, and decreasing disability level on the RMDQ after 4 weeks.

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.

The usage of a modified straight-leg raise neurodynamic test and hamstring flexibility for diagnosis of non-specific low back pain: A cross-sectional study.

OBJECTIVES: The main purpose of this research study was to compare mean modified straight-leg raise test (mSLR) and hamstring muscle length (HL) between chronic non-specific low back pain (LBP) and healthy subjects to understand the possibility of neuropathic causes in LBP population as it may impact the diagnosis and treatment of LBP. Another purpose was to compare mean mSLR between those with lumbar nerve root impingement and those without as determine by magnetic resonance imaging (MRI). METHODS: The design of the study is cross sectional and included 32 subjects with ages ranging from 18-50 years old. Clinical exam objective measures were collected such as patient questionnaires, somatosensory tests, HL range of motion, and a mSLR test, and were compared to the findings from a structural lumbar spine MRI. RESULTS: There were no significant differences in mean HL angulation and mSLR angulation between LBP and healthy subjects (p>0.05). There was no significant difference in mean HL by impingement by versus no impingement (38.3±15.6 versus 44.8±9.4, p = 0.08, Cohen's d = 0.50). On the other hand, there was a significant difference in mean mSLR angulation by impingement (57.6.3±8.7 versus 63.8±11.6, p = 0.05, Cohen's d = 0.60). CONCLUSIONS: The mSLR test was found to be associated with lumbar nerve root compression, regardless of the existence of radiating leg symptoms, and showed no association solely with the report of LBP. The findings highlight the diagnostic dilemma facing clinicians in patients with chronic nonspecific LBP with uncorrelated neuroanatomical image findings. Clinically, it may be necessary to reevaluate the common practice of exclusively using the mSLR test for patients with leg symptoms. This study may impact the way chronic LBP and neuropathic symptoms are diagnosed, potentially improving treatment methods, reducing persistent symptoms, and ultimately improving disabling effects.

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.

Acute fatigue-induced alterations in hamstring muscle properties after repeated Nordic hamstring exercises.

This study aimed to investigate the impact of the Nordic hamstring exercises (NHE) on acute fatigue-induced alterations in the mechanical and morphological properties of hamstring muscles. The second aim was to define the blood flow and perfusion after NHE in recreational active volunteers. Twenty-two individuals volunteered to participate in the study. This study investigated fatigue outcomes: rate of perceived exertion (RPE) scale and average force generated during NHE; mechanical properties (stiffness); morphological properties (thickness, pennation angle, and fascicle length), and vascularity index (VI) of the semitendinosus (ST) and biceps femoris long head (BFLH) at baseline, immediately post-exercise and 1-h post-exercise. The NHE fatigue procedure consisted of six bouts of five repetitions. The results showed an increase in thickness and pennation angle of BFLH and ST immediately post-exercise and a decrease in thickness and pennation angle of BFLH and ST 1-h post-exercise. While the fascicle length of BFLH and ST decreased immediately post-exercise and increased 1-h post-exercise. The VI for two muscles increased immediately post-exercise and after 1-h post-exercise. Moreover, we found a relationship between RPE and average force, that is, as RPE increased during NHE, average force decreased. In conclusion, eccentric NHE exercises significantly and acutely affect BFLH and ST. The NHE fatigue protocol significantly affected the mechanical and morphological properties of BFLH and ST muscles, changing their thickness, fascicle length, pennation angle, and VI.

The need for speed - Does the force-velocity property significantly alter strain distributions within skeletal muscle?

Skeletal muscles are complex structures with nonlinear constitutive properties. This complexity often requires finite element (FE) modeling to better understand muscle behavior and response to activation, especially the fiber strain distributions that can be difficult to measure in vivo. However, many FE muscle models designed to study fiber strain do not include force-velocity behavior. To investigate force-velocity property impact on strain distributions within skeletal muscle, we modified a muscle constitutive model with active and passive force-length properties to include force-velocity properties. We implemented the new constitutive model as a plugin for the FE software FEBio and applied it to four geometries: 1) a single element, 2) a multiple-element model representing a single fiber, 3) a model of tapering fibers, and 4) a model representing the bicep femoris long head (BFLH) morphology. Maximum fiber velocity and boundary conditions of the finite element models were varied to test their influence on fiber strain distribution. We found that force-velocity properties in the constitutive model behaved as expected for the single element and multi-element conditions. In the tapered fiber models, fiber strain distributions were impacted by changes in maximum fiber velocity; the range of strains increased with maximum fiber velocity, which was most noted in isometric contraction simulations. In the BFLH model, maximum fiber velocity had minimal impact on strain distributions, even in the context of sprinting. Taken together, the combination of muscle model geometry, activation, and displacement parameters play a critical part in determining the magnitude of impact of force-velocity on strain distribution.

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.

Eccentric Hamstring Strength Imbalance among Football and Soccer Athletes.

OBJECTIVES: Hamstring strain injuries (HSI) are common among football and soccer athletes. Eccentric strength imbalance is considered a contributing factor for HSI. There is, however, a paucity of data on hamstring imbalances of soccer and American football athletes as they age and advance in skill level. High school athletes will display greater interlimb discrepancies compared with collegiate and professional athletes. In addition, soccer athletes will exhibit greater hamstring asymmetry than American football athletes. METHODS: Hamstring testing was performed on soccer and American football athletes using the NordBord Hamstring Testing System (Vald Performance, Albion, Australia). Age, sex, weight, sport specialization, and sport level were recorded. Maximum hamstring forces (N), torque (N · m), and work (N · s) were measured. Hamstring imbalance (%) was calculated by dividing the absolute value of the difference in leg forces divided by their sum. One-way analysis of variance and independent sample t tests compared measurements between athlete groups. RESULTS: A total of 631 athletes completed measurements, including 88 high school male soccer, 25 college male soccer, 23 professional male soccer, 83 high school female soccer, 28 college female soccer, 288 high school football, and 96 college football athletes. High school soccer players displayed significantly greater imbalances for torque (P = 0.03) and work (P < 0.01) than football athletes. Imbalances for maximum force (P = 0.035), torque (P = 0.018), and work (P = 0.033) were significantly higher for male soccer athletes in high school compared with college- and professional-level athletes. Female high school soccer players had significantly higher imbalance in torque (P = 0.045) and work (P = 0.001) compared with female collegiate soccer players. Football athletes did not experience significant changes in force imbalances between skill levels. CONCLUSIONS: High school soccer athletes exhibit greater hamstring imbalances than football athletes. Higher levels of play in soccer, for both male and female athletes, correlate with less hamstring asymmetry.

Stress-strain relationship of individual hamstring muscles: A human cadaver study.

The incidence of hamstring muscle strain varies among muscles, suggesting that the mechanical stresses associated with elongation may differ among muscles. However, the passive mechanical properties of whole human muscles have rarely been directly measured and clarified. This study aimed to clarify the stress-strain relationship of the hamstring muscles using a soft-embalmed Thiel cadaver. The long heads of the biceps femoris (BFlh), semimembranosus (SM), and semitendinosus (ST) muscles were dissected from eight cadavers. The proximal and distal hamstring tendons were affixed to the mechanical testing machine. Slack length was defined as the muscle length at the initial loading point detected upon the application of a tensile load. Muscle length was measured using a tape measure, and the anatomical cross-sectional area (ACSA) of the muscle was measured at the proximal and distal sites using B-mode ultrasonography. In the loading protocol, the muscle was elongated from its slack length to a maximum of 8% strain at an average rate of 0.83 L0/s, and the amount of displacement and tensile load were measured for each muscle. Further, the strain (%, displacement/slack muscle length) and stress (kPa, tensile load/ACSA) were calculated to evaluate the mechanical properties. Two-way repeated-measures analysis of variance (ANOVA) was used to compare stress changes with increasing muscle strain. A significant interaction between the muscle and strain factors was observed with respect to stress. Post-hoc tests revealed higher stresses in the BFlh and SM than in ST after 3% strain (P < 0.01). However, no significant differences were observed between the BFlh and SM groups. At 8% strain, the BFlh, SM, and ST exhibited stresses of 63.7 ± 12.1, 53.7 ± 23.2, and 21.0 ± 11.9 kPa, respectively. The results indicate that the stress changes associated with muscle strain differed among muscles. In particular, the stress applied to the three muscles at the same strain was found to be higher in the BFlh and SM. Thus, these findings suggest that increased mechanical stress during elongation may contribute to the frequent occurrence of muscle strain in BFlh and SM.

Changes in hamstring contractile properties during the competitive season in young football players.

Background: The study aimed to examine alterations and imbalances in hamstring muscle contractile properties among young football players throughout their competitive season, and to understand how these changes might contribute to the risk of muscle injuries. Hamstring injuries are particularly common in football, yet the underlying causes and effective prevention methods remain unclear. Methods: The research involved 74 young footballers who were assessed before the season (pre-test) and after 12 weeks of training (post-test). To evaluate changes in hamstring muscle contractile properties, specifically the left and right biceps femoris (BF) and semitendinosus (ST), tensiomyography (TMG) parameters were utilized. Results: In comparison to the BF muscle, significant differences in time delay (Td) between the left and right sides in the post-test (p = 0.0193), and maximal displacement (Dm) between the left and right sides at the pre-test (p = 0.0395). However, significant differences in Dm were observed only in the left ST muscle between the pre- and post-tests (p = 0.0081). Regarding lateral symmetry, BF registered measurements of 79.7 ± 13.43 (pre-test) and 77.4 ± 14.82 (post-test), whereas ST showed measurements of 87.0 ± 9.79 (pre-test) and 87.5 ± 9.60 (post-test). Conclusions: These assessments provided TMG reference data for hamstring muscles in young footballers, both before the season and after 12 weeks of in-season training. The observed changes in the contractile properties and decrease in lateral symmetry of the BF in both tests suggest an increased risk of injury.

Individual distribution of muscle hypertrophy among hamstring muscle heads: Adding muscle volume where you need is not so simple.

PURPOSE: The aim of this study was to determine whether a 9-week resistance training program based on high load (HL) versus low load combined with blood flow restriction (LL-BFR) induced a similar (i) distribution of muscle hypertrophy among hamstring heads (semimembranosus, SM; semitendinosus, ST; and biceps femoris long head, BF) and (ii) magnitude of tendon hypertrophy of ST, using a parallel randomized controlled trial. METHODS: A total of 45 participants were randomly allocated to one of three groups: HL, LL-BFR, and control (CON). Both HL and LL-BFR performed a 9-week resistance training program composed of seated leg curl and stiff-leg deadlift exercises. Freehand 3D ultrasound was used to assess the changes in muscle and tendon volume. RESULTS: The increase in ST volume was greater in HL (26.5 ± 25.5%) compared to CON (p = 0.004). No difference was found between CON and LL-BFR for the ST muscle volume (p = 0.627). The change in SM muscle volume was greater for LL-BFR (21.6 ± 27.8%) compared to CON (p = 0.025). No difference was found between HL and CON for the SM muscle volume (p = 0.178).There was no change in BF muscle volume in LL-BFR (14.0 ± 16.5%; p = 0.436) compared to CON group. No difference was found between HL and CON for the BF muscle volume (p = 1.0). Regarding ST tendon volume, we did not report an effect of training regimens (p = 0.411). CONCLUSION: These results provide evidence that the HL program induced a selective hypertrophy of the ST while LL-BFR induced hypertrophy of SM. The magnitude of the selective hypertrophy observed within each group varied greatly between individuals. This finding suggests that it is very difficult to early determine the location of the hypertrophy among a muscle group.