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.

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.

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.

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.

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.

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.

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 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.

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.

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.

Changes in passive and active hamstrings shear modulus are not related after a warmup protocol.

This study aimed to determine whether changes in hamstrings passive and active shear modulus after a warmup protocol are correlated. Twenty males without a history of hamstring strain injury participated. Muscle shear modulus was assessed using ultrasound-based shear wave elastography at rest and during isometric contractions at 20% of maximal voluntary isometric effort before and immediately after a warmup protocol. Changes in passive shear modulus did not seem to be associated with changes in active shear modulus. The results of this study suggest that changes in passive and active hamstring shear modulus are not associated after a standardized warmup intervention.

Adaptive Force of hamstring muscles is reduced in patients with knee osteoarthritis compared to asymptomatic controls.

BACKGROUND: Quadriceps strength deficits are known for patients with knee osteoarthritis (OA), whereas findings on hamstrings are less clear. The Adaptive Force (AF) as a special neuromuscular function has never been investigated in OA before. The maximal adaptive holding capacity (max. isometric AF; AFisomax) has been considered to be especially vulnerable to disruptive stimuli (e.g., nociception). It was hypothesized that affected limbs of OA patients would show clear deficits in AFisomax. METHODS: AF parameters and the maximal voluntary isometric contraction (MVIC) of hamstrings were assessed bilaterally comparing 20 patients with knee OA (ART) vs. controls (CON). AF was measured by a pneumatically driven device. Participants were instructed to maintain a static position despite an increasing load of the device. After reaching AFisomax, the hamstrings merged into eccentric action whereby the force increased further to the maximum (AFmax). MVIC was recorded before and after AF trials. Mixed ANOVA was used to identify differences between and within ART and CON (comparing 1st and 2nd measured sides). RESULTS: AFisomax and the torque development per degree of yielding were significantly lower only for the more affected side of ART vs. CON (p ≤ 0.001). The percentage difference of AFisomax amounted to - 40%. For the less affected side it was - 24% (p = 0.219). MVIC and AFmax were significantly lower for ART vs. CON for both sides (p ≤ 0.001). Differences of MVIC between ART vs. CON amounted to - 27% for the more, and - 30% for the less affected side; for AFmax it was - 34% and - 32%, respectively. CONCLUSION: The results suggest that strength deficits of hamstrings are present in patients with knee OA possibly attributable to nociception, generally lower physical activity/relief of lower extremities or fear-avoidance. However, the more affected side of OA patients seems to show further specific impairments regarding neuromuscular control reflected by the significantly reduced adaptive holding capacity and torque development during adaptive eccentric action. It is assumed that those parameters could reflect possible inhibitory nociceptive effects more sensitive than maximal strengths as MVIC and AFmax. Their role should be further investigated to get more specific insights into these aspects of neuromuscular control in OA patients. The approach is relevant for diagnostics also in terms of severity and prevention.

Relationships Between Modifiable Risk Factors of Hamstring Strain Injury.

ABSTRACT: Ripley, NJ, Comfort, P, and McMahon, JJ. Relationships between modifiable risk factors of hamstring strain injury. J Strength Cond Res 38(3): 510-516, 2024-The aims of this study were to determine whether any relationship exists between eccentric hamstring strength and isokinetic strength imbalances and bicep femoris long head (BF LH ) architecture. Eighteen physically active men (age 24.7 ± 4.3 years, height 181.9 ± 7.2 cm, mass 84.9 ± 12.9 kg) had resting BF LH muscle architecture assessed using ultrasound, with images taken at the midmuscle belly. Measures of isokinetic strength of the knee extensors and flexors involved subjects performing 3 maximal effort repetitions of concentric knee extension and eccentric knee flexion at 60°·s -1 . Good-excellent relative reliability (intraclass correlation coefficient ≥0.86) and low variability (coefficient of variation <10%) were observed for all variables. Relative BF LH fascicle length (FL) demonstrated significant moderate-to-nearly-perfect associations with isokinetic measures identified as hamstring strain injury risk factors ( p < 0.05, r = 0.38-0.92), whereas absolute BF LH FL was not significantly or meaningfully associated with isokinetic measures ( p = 0.07-0.961, r = 0.01-0.30). Relative BF LH FL should be considered when assessing resting BF LH muscle architecture because it is potentially a more appropriate measure of injury risk because of its greater association with strength measures. However, absolute BF LH FL may have a greater usefulness during growth, maturation, and individual proportions.

The Effects of Dry Needling on Hamstring Range of Motion: A Critically Appraised Topic.

CLINICAL SCENARIO: Hamstring range of motion (ROM) and the influence it has on injury risk is among great discussion in the literature. Hamstring injury may result from hamstring tightness, poor flexibility, or decreased ROM, and many argue that this can be prevented through various intervention strategies. In active populations, risk of further injury, pain, and complications throughout the kinetic chain can occur if minimal hamstring ROM is left untreated. One therapeutic intervention that has been applied to varying parts of the body to help improve function while relieving pain is dry needling (DN). This intervention includes the application of needles to structures to induce responses that might benefit healing and overall stimulation of a neurological response. In this review, the intent is to identify evidence and the effects of DN on hamstring ROM. CLINICAL QUESTION: What are the effects of DN on hamstring ROM? SUMMARY OF KEY FINDINGS: Among total 11 articles, 1 single-blinded randomized controlled trial and 2 double-blinded randomized controlled trials were included in this critically appraised topic. All 3 articles had inconclusive evidence to isolate the application of the DN intervention. There was insufficient evidence to identify if DN independently improved hamstring ROM; however, in combination with interventions such as exercise and stretch plans, there were improvements on ROM. CLINICAL BOTTOM LINE: DN does not significantly increase or decrease the ROM of the hamstrings. When combined with exercise and stretch plans, DN could increase ROM. STRENGTH OF RECOMMENDATION: The grade of B is recommended by the Strength of Recommendation Taxonomy for inconsistent or limited-quality patient-oriented evidence.

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

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

Hamstring stiffness and injury risk factors during the handball season in female players.

Monitoring the muscle mechanical properties and functions of female athletes throughout their training season is relevant to understand the relationships between these factors and to predict noncontact injuries, which are prevalent among female athletes. The first aim of this study was to determine whether female handball players' passive stiffness of the hamstring muscles is associated with hamstring extensibility, strength of knee flexors and extensors, and lower limb stiffness. Additionally, the study monitored fluctuations in these factors over 25 weeks. The study utilized an isokinetic dynamometer to record hamstring passive stiffness, extensibility, and hamstring and quadriceps strength of 18 young handball players. Lower limb stiffness was determined from a countermovement vertical jump conducted on a force plate. The countermovement jump involved the calculation of the peak force during the eccentric phase and the mean force during the concentric phase. The results showed a positive correlation between hamstring passive stiffness and lower limb stiffness (r = 0.660, p < 0.01), knee flexion and extension strength (r = 0.592, p < 0.01 and r = 0.497, p < 0.05, respectively), and eccentric peak force (r = 0.587, p < 0.01) during jumping. The strength of knee extensors increased significantly after 6 weeks, and hamstring stiffness after 12 weeks of training. In conclusion, the increased hamstring stiffness following training did not match other factors associated with injury risk. Therefore, preventing multifactorial injury risk requires a comprehensive approach, and monitoring one factor alone is insufficient to predict noncontact injuries in female handball players.