MEDIAL AND LATERAL HAMSTRINGS RESPONSE AND FORCE PRODUCTION AT VARYING DEGREES OF KNEE FLEXION AND TIBIAL ROTATION IN HEALTHY INDIVIDUALS

A new field-test for assessing the medial and lateral hamstring strength at long-muscle length

This research investigates the influence of tibial rotations with knee flexion (KF) on the electromyographic (EMG) activities of hamstring muscles (HM) groups and the strength ratio between the medial and lateral rotation of the tibia. A cross-sectional design was employed to assess muscle activity, isometric strength and reliability. The research was conducted in a controlled laboratory environment. Thirty-six amateur male athletes were recruited as volunteers. The measures included peak muscle activity of the semitendinosus and biceps femoris long head, the knee flexors' isometric strength ratio and reliability. The isometric strength ratios of medial (MR) to lateral (LR) tibial rotations were 0.94 ± 0.17 at 90°, and 0.93 ± 0.10 at both 60° and 30° of KF angulation. Tibial position significantly influenced knee flexion strength as well as HM activity, irrespective of KF angulation. Specifically, biceps femoris activity increased by 33.6% in LR compared to MR, while semitendinosus activity increased by 22.6% in MR compared to LR. The Knee-Rotation test (KR-test) can be a valuable tool for evaluating both HM groups (ICC >0.87), and identifying the primary target for strengthening purposes during the injury prevention process. It provides insights for effective rehabilitation and training interventions.

Influence of exercise-induced hamstrings fatigue on proprioceptive reweighting strategies and postural performance in bipedal stance in recreational athletes

OBJECTIVE

An optimal proprioceptive reweighting strategy is necessary to maintain posture. A suboptimal strategy was associated with injury determinants and whether the strategy can be modified is unknown. Muscle fatigue can be used to investigate proprioceptive reweighting. The aims of this study were to evaluate the effects of local fatigue on proprioceptive reweighting strategies and postural stability as well as relationships between fatigue and these postural parameters.

DESIGN

Fourteen recreational athletes were included. Relative proprioceptive weighting (RPW) was characterized according to the perturbation of the center of pressure (CoP) displacement generated by muscle vibration on a firm and foam surface. RPW evolution <95 % indicated that individuals were able to reweight proprioception from the ankle to lumbar signals according to the surface while evolution >105 % indicated that athletes maintained an ankle-steered strategy. Student's t-tests were used to compare RPW evolution, CoP velocity, and root mean square (RMS) before and after exercise-induced hamstring fatigue. Spearman's rank correlation coefficient was used to test the relationship between fatigue variables, RPW evolution, and stability variables.

RESULTS

Hamstring fatigue induced an ankle-steered strategy characterized by an increase in RPW evolution when the surface was changed (P = 0.002) and an increase in CoP velocity (P = 0.045) and CoP RMS (P = 0.005) on firm surface. None of the correlation coefficients testing the relationship between the parameters proved to be significant.

CONCLUSION

Local fatigue leads to suboptimal proprioceptive reweighting strategies and impaired stability on firm surface. Results suggests that proprioceptive reweighting strategies are modifiable. Whether this predisposes participants to injury remains to be defined.

Hamstrings force-length relationships and their implications for angle-specific joint torques: a narrative review

Temporal biomechanical and physiological responses to physical activity vary between individual hamstrings components as well as between exercises, suggesting that hamstring muscles operate differently, and over different lengths, between tasks. Nevertheless, the force-length properties of these muscles have not been thoroughly investigated. The present review examines the factors influencing the hamstrings’ force-length properties and relates them to in vivo function. A search in four databases was performed for studies that examined relations between muscle length and force, torque, activation, or moment arm of hamstring muscles. Evidence was collated in relation to force-length relationships at a sarcomere/fiber level and then moment arm-length, activation-length, and torque-joint angle relations. Five forward simulation models were also used to predict force-length and torque-length relations of hamstring muscles. The results show that, due to architectural differences alone, semitendinosus (ST) produces less peak force and has a flatter active (contractile) fiber force-length relation than both biceps femoris long head (BFlh) and semimembranosus (SM), however BFlh and SM contribute greater forces through much of the hip and knee joint ranges of motion. The hamstrings’ maximum moment arms are greater at the hip than knee, so the muscles tend to act more as force producers at the hip but generate greater joint rotation and angular velocity at the knee for a given muscle shortening length and speed. However, SM moment arm is longer than SM and BFlh, partially alleviating its reduced force capacity but also reducing its otherwise substantial excursion potential. The current evidence, bound by the limitations of electromyography techniques, suggests that joint angle-dependent activation variations have minimal impact on force-length or torque-angle relations. During daily activities such as walking or sitting down, the hamstrings appear to operate on the ascending limbs of their force-length relations while knee flexion exercises performed with hip angles 45–90° promote more optimal force generation. Exercises requiring hip flexion at 45–120° and knee extension 45–0° (e.g. sprint running) may therefore evoke greater muscle forces and, speculatively, provide a more optimum adaptive stimulus. Finally, increases in resistance to stretch during hip flexion beyond 45° result mainly from SM and BFlh muscles.

Postoperative external tibial rotation is correlated with inferior meniscal healing following pullout repair of a medial meniscus posterior root tear

PURPOSE

The purpose of this study was to evaluate the influence of tibial rotation on the postoperative healing status of the medial meniscus (MM) following pullout repair of the MM posterior root tear (MMPRT).

METHODS

Ninety-one patients (68 women and 23 men; mean age 63.3 ± 8.8 years) who had undergone transtibial pullout repair of MMPRT were enrolled in the study. The tibial external rotation angle (ERA) in each patient was measured postoperatively using computed tomography in the extended knee position. The meniscal healing status following transtibial pullout repair was assessed by second-look arthroscopy (mean postoperative period 12 months) using a previously published scoring system (range 0-10). The association between the ERA and the meniscal healing score was investigated using univariate linear regression models. The ERA cut-off for improved meniscal healing score (≥ 7) was determined using receiver-operating characteristic analysis.

RESULTS

The ERA and the meniscal healing score were significantly associated, confirming that increased ERAs were correlated with worse meniscal healing status (R =  - 0.28; P < 0.001). The optimum ERA cut-off value was 0.5°, with a sensitivity of 68% and a specificity of 63%. The mean meniscal healing scores were 7.3 and 6.2 among patients with ERAs < 0.5° and those with ERAs ≥ 0.5°, respectively (P < 0.001).

CONCLUSION

This study demonstrated that the ERA was significantly correlated with the postoperative meniscal healing status. Postoperative tibial rotation could be one of the factors affecting postoperative outcomes of pullout repair of MMPRT. Controlling the tibial rotation may possibly improve meniscal healing.

LEVEL OF EVIDENCE

III.

Hamstring Strain Injury Rehabilitation

Hamstring strain injuries are common among athletes and often require rehabilitation to prepare players for a timely return to sport performance while also minimizing reinjury risk. Return to sport is typically achieved within weeks of the injury; however, subsequent athlete performance may be impaired, and reinjury rates are high. Improving these outcomes requires rehabilitation practitioners (eg, athletic trainers and physical therapists) to understand the causes and mechanisms of hamstring strain injury, know how to perform a thorough clinical examination, and progress loading to the site of injury safely and effectively. This narrative review discusses current clinical concepts related to these aspects of rehabilitation for hamstring strain injury, with the aim of helping practitioners improve athletes' outcomes. Collectively, this knowledge will inform the implementation of evidence-based rehabilitation interventions.

Short-term isokinetic and isometric strength outcomes after anterior cruciate ligament reconstruction in adolescents

OBJECTIVES

To examine differences in knee strength outcomes after ACL reconstruction according to quadriceps tendon (QT) or hamstring tendon (HT) autograft in adolescents.

DESIGN

Retrospective cohort.

METHODS

Surgical and clinical outcome data were collected. Analyses were conducted separately for female and male cohorts and grouped by graft type (HT or QT). A Mann-Whitney U test of independent samples was used to examine group differences according to graft type.

RESULTS

107 females (age = 15.6 ± 1.5 years) and 94 males (age = 15.7 ± 1.5 years) were included. Mean time since surgery ranged from 7.2 to 7.9 months. Those with a QT autograft had decreased normalized isokinetic quadriceps peak torque on the involved limb compared to the HT group (p < 0.01, ES = 0.71-0.89). Normalized isometric hamstring peak torque was decreased for those with HT autograft in the female cohort (p = 0.02, ES = 0.57).

CONCLUSION

Normalized isokinetic quadriceps peak torque was reduced by 18-20% on the involved limb in those with a QT autograft. Normalized isometric hamstring peak torque was decreased by 13% for those with HT autograft in the female cohort. Method of strength testing may be an important consideration to fully appreciate strength deficits after ACL reconstruction according to graft type.

Superimposing hip extension on knee flexion evokes higher activation in biceps femoris than knee flexion alone

Hamstring muscle function during knee flexion has been linked to hamstring injury and performance. However, it is unclear whether knee flexion alone (KF) requires similar hamstring electromyography (EMG) activity pattern to simultaneous hip extension and knee flexion (HE-KF), a combination that occurs in the late swing phase of sprinting. This study examined whether HE-KF maximal voluntary isometric contraction (MVIC) evokes higher (EMG) activity in biceps femoris long head (BFlh) and semitendinosus (ST) than KF alone. Effects of shank rotation angles were also tested. Twenty-one males performed the above-mentioned MVICs while EMG activity was measured along ST and BFlh. Conditions were compared using a one-way mixed functional ANOVA model under a fully Bayesian framework. Higher EMG activity was found in HE-KF in all shank rotation positions than in KF in the middle region of BFlh (highest in the 9th channel, by 0.022 mV [95%CrI 0.014 to 0.030] in neutral shank position). For ST, this was only observed in the neutral shank position and in the most proximal channel (by 0.013 mV [95%CrI 0.001 to 0.025]). We observed muscle- and region-specific responses to HE-KF. Future studies should examine whether hamstring activation in this task is related to injury risk and sprint performance.

Electromyographic Comparison of Five Lower-Limb Muscles between Single- and Multi-Joint Exercises among Trained Men

Resistance-training exercises can be classified as either single- or multi-joint exercises and differences in surface electromyography (EMG) amplitude between the two training methods may identify which muscles can benefit from either training modality. This study aimed to compare the surface EMG amplitude of five hip- and knee extensors during one multi-joint (leg press) and two single-joint exercises (knee extension and kickback). Fifteen resistance-trained men completed one familiarization session to determine their unilateral six repetitions maximum (6RM) in the three exercises. During the following experimental session, EMG amplitudes of the vastus lateralis, vastus medialis, rectus femoris, gluteus maximus and biceps femoris of the left leg were measured while performing three repetitions on their respective 6RM loads. The multi-joint exercise leg press produced higher EMG amplitude of the vastus lateralis (ES = 0.92, p = 0.003) than the single-joint exercise knee extension, whereas the rectus femoris demonstrated higher EMG amplitude during the knee extension (ES = 0.93, p = 0.005). The biceps femoris EMG amplitude was higher during the single-joint exercise kickback compared to the leg press (ES = 2.27, p < 0.001), while no significant differences in gluteus maximus (ES = 0.08, p = 0.898) or vastus medialis (ES = 0.056, p = 0.025 were observed between exercises. The difference in EMG amplitude between single- and multi-joint exercises appears to vary depending on the specific exercises and the muscle groups tested. Leg press is a viable and time-efficient option for targeting several hip- and knee extensors during resistance training of the lower limbs, but the single-joint exercises may be preferable for targeting the rectus femoris and biceps femoris.