It is unclear how hamstring stiffness influences lower limb muscle activation during jump-landing mechanics. The study aimed to investigate the role of the hamstring stiffness on lower limb muscle recruitment during jumping manoeuvres. Thirty male athletes were recruited and allocated into high- and low-stiffness groups. Hamstring stiffness was determined as the average stiffness of bilateral hamstrings using a MyotonPRO. Surface electromyography of the bilateral gluteus maximus, quadriceps, and hamstring muscles was assessed during the takeoff, at ground contact, and at landing, while ground reaction force (GRF) was measured during the squat jump, countermovement jump, and drop vertical jump. The results showed that athletes with greater hamstring stiffness exhibited a higher median frequency of the lateral hamstrings in both limbs and the vastus medialis in the dominant limb than the low-stiffness group during takeoff, adjustment, and landing phases for all vertical jumps. The high stiffness group landed with lower vertical GRF in the drop vertical jump. In conclusion, athletes with high hamstring stiffness showed greater motor unit recruitment during takeoff and landing phases. This recruitment did not influence takeoff performance but aid with absorbing landing force. Therefore, the contribution of the lower limb muscle stiffness should be considered in sports activities.

This study aimed to investigate the hamstring onset time and recruitment level during jumping tasks in athletes with chronic hamstring strain injuries. Thirteen hamstring injured athletes and thirteen matched healthy athletes were recruited. Activation onset time and muscle recruitment (median frequency of the EMG) of the lateral hamstring (LH) and medial hamstring (MH) was measured during double leg jumps in vertical and horizontal directions on the force platforms. The peak vertical ground reaction force and loading rate were obtained for all jumps. The injured group showed a delayed onset time (p = 0.029) and a lower recruitment of the LH during the landing (p = 0.018) than the control group. Activation deficits in the injured group led to a higher landing force and loading rate. Additionally, the LH and MH were lesser recruited in the vertical direction than the horizontal directions in the landing. In conclusion, athletes with hamstring injuries show hamstring activation deficits of the injured leg during jumping leading to degrading jump-landing performance. Also, jumping in different directions play a role to modify the recruitment of the hamstrings in the injured athletes. Therefore, movement plane is suggested to be considered in clinical rehabilitation for the hamstring injury.

Purposes: Cartilage thickness could be a significant biomarker for the early identification of knee osteoarthritis. However, reference data on cartilage thickness across various age groups are still lacking. Consequently, this study aims to establish reference values for cartilage thickness while examining differences related to sex and age groups. Methods: The study included 232 participants. Bilateral measurements of knee articular cartilage thickness were conducted using ultrasound (US) at three anatomical sites: the lateral femoral condyle, medial femoral condyle and intercondylar area. Three readings were taken per site by an experienced radiologist with expertise in musculoskeletal US. The mean cartilage thickness was calculated, and comparisons were performed between sexes using independent samples t ‐tests and across various age groups (young, middle‐aged, older adults and retirement age) using one‐way analysis of variance. Results: Male participants demonstrated significantly higher cartilage thickness than females across all examined locations, except the middle area of the right knee. Notable differences among age groups were seen in the right lateral ( p = 0.002) and medial ( p = 0.019) compartments, along with the left medial compartment ( p = 0.008). Analysis of the male subgroups indicated that those in the retirement age category exhibited greater cartilage thickness in the right lateral and medial compartments, as well as the left medial compartment, compared to other age groups. Conclusion: Males showed greater cartilage thickness than females across most knee areas. Additionally, age‐related variations in cartilage thickness were primarily observed in males, particularly in those of retirement age, while no significant age‐related differences were detected in females. These results underscore the importance of considering sex and age when evaluating knee cartilage health using US. Level of Evidence: Level III.

Background: Non-specific low back pain (NSLBP) is associated with altered neuromuscular control of the lumbopelvic–hip complex (LPHC). However, the functional behavior of the transversus abdominis (TrA) and gluteus medius (GM) during upright postural tasks, with and without the abdominal drawing-in maneuver (ADIM), remains unclear. This study aimed to compare TrA and GM activation between individuals with NSLBP and asymptomatic controls during standing and single-leg stance using rehabilitation ultrasound imaging (RUSI). Methods: Thirty-two participants (16 with NSLBP and 16 asymptomatic controls) underwent RUSI assessment under four task conditions: standing and single-leg stance, with and without ADIM. Muscle function was quantified using thickness change derived from ultrasound measurements. A two-way mixed-model analysis of variance with Bonferroni-adjusted post hoc comparisons was performed. Results: Significant group × condition interactions were identified for TrA activation (p < 0.05). Individuals with NSLBP demonstrated reduced TrA activation during standing with ADIM and reduced GM activation during single-leg stance compared with asymptomatic controls. The effect sizes were moderate to large for TrA activation and small to moderate for GM activation. Conclusions: These findings suggest task-specific differences in neuromuscular activation patterns in individuals with NSLBP. Ultrasound-derived thickness change measures obtained during functional, weight-bearing tasks may provide clinically relevant information to support motor control rehabilitation strategies.