Copers are individuals who have had a lateral ankle sprain but have no history of recurrent lateral ankle sprain, residual symptoms, or functional disability. Copers have shown no significant difference in lower limb kinematics in landing for proactive conditions compared with a control (CTR) group. However, the copers (CPR) group has shown differences compared to CTR and chronic ankle instability (CAI) groups for dynamic balance conditions, suggesting that the trunk may compensate for foot instability during shock absorption. This study aimed to examine the differences in the kinematics and kinetics among CPR, CAI and CTR groups in reactive and proactive single-leg landing tasks. Participants were physically active adults with CAI (n = 14), CPR (n = 14), and CTR (n = 14), who performed proactive and reactive single-leg landings. The lower limb, trunk kinematics, vertical ground reaction force (vGRF) peak value, and the time to minimum peak vGRF were analysed. It might be conceivable that the CPR group could absorb vGRF efficiently by increasing the trunk flexion angle and increasing the time to reach the minimum peak vGRF regardless of landing condition. The results suggest that evaluating the movements of the entire body, including the ankle and trunk, is essential.

Purpose: While changes in muscle quality and quantity are common concerns as knee osteoarthritis (KOA) progresses, it is equally important to consider the central nervous system’s role in regulating muscle force output. This study aimed to elucidate the firing properties of motor units (MUs), muscle quantity, and muscle quality during submaximal isometric contractions in patients with early and severe KOA. Methods: This was a prospective study comparing 30 patients with KOA according to the Kellgren/Lawrence grading system divided into early and severe KOA groups. The participants performed ramp-up and sustained contractions at 10%, 30%, and 60% of their maximal voluntary contraction (MVC). High-density surface electromyography signals were recorded in the vastus medialis (VM) and vastus lateralis (VL) muscles on the affected side. Skeletal muscle quantity and quality were assessed using computed tomography based on cross-sectional area (CSA) and computed tomography attenuation value (CTV), respectively. Results: The CSA of the VM muscle was significantly smaller in the severe KOA group than in the early KOA group (p = 0.021). A total of 682 MUs were detected (early KOA, n = 348, severe KOA, n = 334). The ramp-down phase of the discharge rate (DR) of MUs recruited by the VL muscle in the severe KOA group was significantly lower than that in the early KOA group (p = 0.004). In addition, the knee extension torque of patients with early KOA was significantly correlated with the CSA of the VM muscle (r = 0.405) and the DR obtained at 30% MVC of the VM (r = 0.503) and VL (r = 0.610) muscle. Furthermore, the knee extension torque in patients with severe KOA was significantly correlated with the CTV of the VM (r = 0.677) and VL (r = 0.599) muscles. Conclusions: In patients with severe KOA, a small CSA of the VM is associated with a characteristic DR pattern depending on the contraction level. The VM and VL muscles fired without a hierarchical pattern in the early and severe KOA groups. These findings suggest that neuromuscular degeneration may occur not only in patients with severe KOA but also in patients with early KOA.

Background This study aimed to evaluate the safety and effectiveness of knee exercise within four hours after total knee arthroplasty (TKA) using a single-joint hybrid assistive limb (HAL-SJ). Materials and methods This pilot single-blind randomized controlled trial included participants who underwent TKA for osteoarthritis and were randomly allocated to the early rehabilitation (n = 14) or control rehabilitation (n = 16) group. Knee rehabilitation exercises using the HAL-SJ began within four hours postoperatively in the early group and seven days after surgery in the control group. Knee circumference, range of motion (ROM), pain, muscle strength, and extension lag were assessed before and one and two weeks after surgery. Results Circumferences at 1 and 10 cm from the upper edge of the patella did not differ between the groups before surgery or one week postoperatively. The extension lag and knee flexion ROM after one week were significantly better in the early intervention group than in the control group. However, the quadriceps and hamstring isometric knee strength and pain scores did not differ between the groups at one and two weeks postoperatively. HAL-SJ-related complications were not reported. Conclusion Rehabilitation knee exercises using the HAL-SJ within four hours after TKA improved extension lag and knee flexion ROM without exacerbating knee swelling and pain.

Background/Objectives: This single-center cohort study investigated preoperative risk factors such as physical function, quantity, and quality of the quadriceps femoris for physical activity (PA) 1 year after total knee arthroplasty (TKA). Methods: This study included 204 patients with knee osteoarthritis who underwent TKA; they were divided into increased and decreased PA groups. Items with significant differences between the two groups in non-operative-side quadriceps strength, knee injury and osteoarthritis outcome scores (KOOS), Sport/Rec scores, operative-side cross-sectional area (CSA) of the vastus medialis (VM), and operative-side computed tomography attenuation values (CTV) of the vastus lateralis (VL) were fitted in the multiple logistic regression analysis. The cutoff value of the preoperative CSA of the VM required for PA to exceed the required points at 1 year postoperatively was calculated using the receiver operating characteristic (ROC) curve. Results: Multivariate logistic regression analysis showed that the non-operative-side quadriceps strength KOOS sport/rec, operative-side CSA of VM, and operative-side CTV of the VL were significantly associated with increased PA after TKA. The ROC-calculated cutoff value was 10.2 cm². Conclusions: These results suggested that preoperative muscle quantity and quality, particularly in the VM, could play important roles in postoperative PA outcomes after TKA.