Muscle co-activation in the elderly contributes to control of hip and knee joint torque and endpoint force.

We investigated the coordinated activity patterns of muscles based on cosine tuning in the elderly during an isometric force exertion task. We also clarified whether these coordinated activity patterns contribute to the control of hip and knee joint torque and endpoint force as co-activation. Preferred direction (PD) of activity for each muscle in 10 young and 8 older males was calculated from the lower limb muscle activity during isometric force exertion task in various directions. The covariance of endpoint force (η) was calculated from the exerted force data using a force sensor. Relationship between PD and η was used to examine the effect of muscle co-activation on the control of endpoint force. Co-activation between rectus femoris and semitendinosus/biceps femoris increased with changes in muscle PD. Additionally, the η values were significantly low, suggesting that co-activation of multiple muscles may contribute to endpoint force exertion. The mechanism for cooperative muscle activity is determined by the cosine tuning of the PD of each muscle, which affects the generation of hip and knee joint torque and endpoint force exertion. Co-activation of each muscle's PD changes with age, causing increased muscle co-activation to control torque and force. We demonstrated that co-activation in the elderly is a stabilizer of unsteady joints and a muscle control strategy for cooperative muscle activity.

Clinical utility of markerless motion capture for kinematic evaluation of sit-to-stand during 30 s-CST at one year post total knee arthroplasty: a retrospective study.

BACKGROUND: Although the importance of kinematic evaluation of the sit-to-stand (STS) test of total knee arthroplasty (TKA) patients is clear, there have been no reports analyzing STS during the 30-s chair sit-up test (30 s-CST) with a focus on kinematic characteristics. This study aimed to demonstrate the clinical utility of kinematic analysis of STS during the 30 s-CST by classifying STS into subgroups based on kinematic parameters, and to determine whether differences in movement strategies are expressed as differences in clinical outcomes. METHODS: The subjects were all patients who underwent unilateral TKA due to osteoarthritis of the knee and were followed up for one year postoperatively. Forty-eight kinematic parameters were calculated using markerless motion capture by cutting STS in the 30 s-CST. The principal components of the kinematic parameters were extracted and grouped by kinematic characteristics based on the principal component scores. Clinical significance was examined by testing whether differences in patient-reported outcome measures (PROMs) were observed. RESULTS: Five principal components were extracted from the 48 kinematic parameters of STS and classified into three subgroups (SGs) according to their kinematic characteristics. It was suggested that SG2, using a kinematic strategy similar to the momentum transfer strategy shown in previous studies, performed better in PROMs and, in particular, may be associated with achieving a "forgotten joint", which is considered the ultimate goal after TKA. CONCLUSIONS: Clinical outcomes differed according to kinematic strategies used STS, suggesting that kinematic analysis of STS in 30 s-CST may be useful in clinical practice. TRIAL REGISTRATION: This study was approved by the Medical Ethical Committee of the Tokyo Women's Medical University (approval number: 5628 on May 21, 2021).

The investigation of an analysis method for co-activation of knee osteoarthritis utilizing normalization of peak dynamic method.

BACKGROUND: Assessing co-activation characteristics in knee osteoarthritis (knee OA) using method of quantification of the activity ratio (such as the co-contraction index (CCI) or the directed co-activation ratios (DCAR)) for surface electromyography (EMG) has been reported. However, no studies have discussed the differences in results between non-negative matrix factorization (NNMF) and the DCAR. RESEARCH QUESTION: Does DCAR or NNMF reflect the characteristic co-activation pattern of knee OA while using EMG normalized by the peak dynamic method? METHODS: Ten elderly control participants (EC) and ten knee OA patients (KOA) volunteered to participate in this study. EMG data from 20 participants were obtained from our previous study. Patients with knee OA were recruited from a local orthopedic clinic. The DCAR of agonist and antagonist muscles and the number of modules using NNMF were calculated to evaluate multiple muscle co-activations. An independent t-test statistical parametric mapping approach was used to compare the DCAR between the two groups. The difference in the number of modules between EC and KOA was evaluated using the Wilcoxon rank-sum test. RESULTS: There was no significant difference in the DCAR between the two groups. However, NNMF had significantly fewer modules with KOA than with EC. SIGNIFICANCE: The NNMF with the ratio of the amplitude of each muscle and duration of activity as variables reflected the co-activation of KOA, characterized by the high synchronous and prolonged activity of each muscle. Therefore, the NNMF is suitable for extracting characteristic muscle activity patterns of knee OA independent of the normalization method.

Effects of Controlling Abnormal Joint Movement on Expression of MMP13 and TIMP-1 in Osteoarthritis.

OBJECTIVE: Abnormal joint movement is associated with osteoarthritis (OA). Previous studies using the controlling abnormal joint movement (CAJM) model of OA reported delayed cartilage degeneration; however, none of them focused on gait performance and the localization of matrix metalloproteinase 13 (MMP13) and tissue inhibitor of metalloproteinase-1 (TIMP-1) in chondrocytes. Therefore, we aimed to investigate the effect of controlling abnormal joint movement on gait performance and the localization of MMP13 and TIMP-1, using kinematic and histological analyses. DESIGN: Rats were assigned to 2 groups: anterior cruciate ligament transection (ACL-T) group and CAJM group (n = 5/group); contralateral hind limbs of ACL-T rats were designated as intact. After 1, 2, and 4 weeks, step length was analyzed, and after 2, 4, and 8 weeks, Safranin O-Fast Green staining and immunohistochemical staining for MMP13 and TIMP-1 were performed. RESULTS: Step length did not differ significantly between the groups. However, degeneration of articular cartilage was higher in the ACL-T group than in the intact group (P < 0.05). There was no significant difference in the CAJM group at all time points. Immunohistochemical analysis of the MMP13/TIMP-1 relationship revealed a significant increase in the expression ratio of MMP13 after 4 weeks in the ACL-T group compared to the CAJM group (P < 0.05). CONCLUSIONS: Controlling abnormal joint movement may reduce mechanical stress owing to kinematic elements of small articulation including joint instability and delayed cartilage degeneration, despite the lack of kinematic change in step length.

Reliability and Validity of the Japanese Version of the Mini-balance Evaluation Systems Test in Patients with Subacute Stroke.

OBJECTIVE: The objective of the current study was to evaluate the reliability and validity of the Japanese version of the Mini-Balance Evaluation Systems Test (J-Mini-BESTest) in patients with subacute stroke. METHODS: Eighteen patients who had suffered a first hemiplegic stroke (mean age, 59.1 ± 27.0 years) and had been admitted to convalescent rehabilitation wards were enrolled. The J-Mini-BESTest, the Berg Balance Scale (BBS), and the functional reach test (FRT) were used to assess balance. Four physical therapists (PTs) observed and scored the J-Mini-BESTest while another PT conducted the test. The interrater reliability of the J-Mini-BESTest was assessed using intraclass correlation coefficients (ICC[2,1]) for the total and section scores, and kappa statistics for each item. Internal consistency of the five raters was assessed using Cronbach's alpha. Concurrent validity of the J-Mini-BESTest was assessed against the BBS and FRT using Spearman's correlation coefficients. RESULTS: The ICC[2,1] of the total and section scores were 0.90 (95% confidence interval: 0.81-0.95) and 0.63-0.85, respectively. Cronbach's alphas were 0.80-0.87. The kappa statistics were 0.47-1.00. The scores of the J-Mini-BESTest were significantly correlated with those of the BBS (rho=0.66, p=0.006) but not with those of the FRT (rho=-0.36, p=0.189). CONCLUSION: The J-Mini-BESTest showed excellent inter-rater reliability and internal consistency. Although the J-Mini-BESTest was not correlated with the FRT, it was significantly correlated with the BBS. The J-Mini-BESTest is a reliable and valid tool for evaluating dynamic balance in patients with subacute stroke.

Controlling Abnormal Joint Movement Inhibits Response of Osteophyte Formation.

Objective Osteoarthritis (OA) is induced by accumulated mechanical stress to joints; however, little has been reported regarding the cause among detailed mechanical stress on cartilage degeneration. This study investigated the influence of the control of abnormal joint movement induced by anterior cruciate ligament (ACL) injury in the articular cartilage. Design The animals were divided into 3 experimental groups: CAJM group ( n = 22: controlling abnormal joint movement), ACL-T group ( n = 22: ACL transection or knee anterior instability increased), and INTACT group ( n = 12: no surgery). After 2 and 4 weeks, the knees were harvested for digital microscopic observation, soft X-ray analysis, histological analysis, and synovial membrane molecular evaluation. Results The 4-week OARSI scores showed that cartilage degeneration was significantly inhibited in the CAJM group as compared with the ACL-T group ( P < 0.001). At 4 weeks, the osteophyte formation had also significantly increased in the ACL-T group ( P < 0.001). These results reflected the microscopic scoring and soft X-ray analysis findings at 4 weeks. Real-time synovial membrane polymerase chain reaction analysis for evaluation of the osteophyte formation-associated factors showed that the mRNA expression of BMP-2 and VEGF in the ACL-T group had significantly increased after 2 weeks. Conclusions Typically, abnormal mechanical stress induces osteophyte formation; however, our results demonstrated that CAJM group inhibited osteophyte formation. Therefore, controlling abnormal joint movement may be a beneficial precautionary measure for OA progression in the future.