Neural Drive and Motor Unit Characteristics of the Serratus Anterior in Individuals With Scapular Dyskinesis.

OBJECTIVE: Scapular dyskinesis is one of the causes of shoulder disorders and involves muscle weakness in the serratus anterior. This study investigated whether motor unit (MU) recruitment and firing property, which are important for muscle exertion, have altered in serratus anterior of the individuals with scapular dyskinesis. METHODS: Asymptomatic adults with (SD) and without (control) scapular dyskinesis were analyzed. Surface electromyography (sEMG) waveforms were collected at submaximal voluntary contraction of the serratus anterior. The sEMG waveform was decomposed into MU action potential amplitude (MUAPAMP), mean firing rate (MFR), and recruitment threshold. MUs were divided into low, moderate, and high thresholds, and MU recruitment and firing properties of the groups were compared. RESULTS: High-threshold MUAPAMP was significantly smaller in the SD group than in the control group. The control group also exhibited recruitment properties that reflected the size principle, however, the SD group did not. Furthermore, the SD group had a lower MFR than the control group. CONCLUSIONS: Individuals with scapular dyskinesis exhibit altered MU recruitment properties and lower firing rates of the serratus anterior; this may be detrimental to muscle performance. Thus, it may be necessary to improve the neural drive of the serratus anterior when correcting scapular dyskinesis.

Impacts of Negative and Positive Life Events on Development of Social Frailty among Community-Dwelling Older Adults.

OBJECTIVES: This study aimed to examine the impact of negative and positive life events on the development of social frailty. DESIGN: Population-based longitudinal study. SETTING AND PARTICIPANTS: This study was set in the Japanese community cohort and included 2174 adults aged ≥65 years without social frailty at baseline. METHODS: We assessed the experiences of 6 negative and positive life events (increase in economic difficulties, illness or injury of spouse, death of family or friends, marriage of children or grandchildren, birth of grandchildren or great-grandchildren, and making new friends) in the 15 months after baseline. We followed the social frailty status of the participants and identified the development of social frailty 48 months after the baseline. Social frailty was operationally defined as having 2 or more of Makizako's 5 items (going out less frequently, rarely visiting friends, not feeling helpful to friends or family, living alone, and not talking to someone daily). RESULTS: Among 2174 participants without social frailty at baseline, 161 (7.4%) developed social frailty after 48 months. Multivariate logistic regression models on each life event and development of social frailty showed that illness or injury of spouse was significantly associated with a higher risk of subsequent social frailty [adjusted odds ratio (OR), 1.74; 95% CI, 1.10-2.74] and making new friends was significantly associated with lower risk of subsequent social frailty (adjusted OR, 0.38; 95% CI, 0.27-0.54). No significant ORs of social frailty were found for other life events. CONCLUSIONS AND IMPLICATIONS: Life events in later life have both positive and negative impacts on the development of social frailty, depending on the nature of the event. To prevent social frailty, it may be important to monitor negative life events and promote positive life events in later life.

Evaluation of the relationship between truss/windlass mechanisms and foot stiffness while walking.

BACKGROUND: The truss/windlass coefficients ware reported as a surrogate parameter for foot stiffness while walking. However, the construct validity and reliability of whether the truss/windlass coefficients reflect foot stiffness have not been sufficiently validated. This study validated the truss/windlass coefficient reflects the construct validity and reliability of foot stiffness. METHODS: Participants were 25 healthy young males (21.6 ± 0.7 years). Foot stiffness was assessed using Simplified Foot Stiffness. It was determined by dividing the difference in foot load between sitting and standing by the rate of change in navicular height. The truss/windlass coefficient was calculated as the behavior of the foot arch during middle to late stance. To assess the reliability of each parameter, intraclass correlation coefficients (ICC 1.1) and Bland-Altman analysis were used, and Spearman's rank correlation coefficients were used to determine construct validity. RESULTS: The truss coefficient (ICC1.1 0.86) and Simplified Foot Stiffness (ICC1.1 0.87) demonstrated high reliability and no systematic error. However, the windlass coefficient (ICC1.1 0.73) demonstrated moderate reliability and proportional error. Furthermore, the truss coefficient had a significant positive correlation with Simplified Foot Stiffness (r = 0.504; p < 0.01), whereas the windlass coefficient did not (r = 0.06; p = 0.67). CONCLUSION: The truss coefficient was proposed as a highly reliable parameter that reflects foot stiffness. However, the windlass coefficient has a proportional error, despite being moderately reliable.

Sex differences in pelvis, thigh, and shank coordination during walking.

Differences in lower limb kinematics between males and females during functional activities may be attributed to sex differences in the incidence of patellofemoral pain, which is more common in females. To better comprehend the knee joint motion, it is necessary to understand both inter-segmental coordination patterns and angular amplitude. This exploratory study aimed to assess sex differences in pelvis-thigh and thigh-shank coordination patterns in the frontal and horizontal planes during walking. Data regarding the kinematic characteristics of the pelvis, thigh, and shank segments were collected from 26 males and 26 females performing walking at self-selected speeds using a 3D motion capture system. Furthermore, we compared the kinematics of the pelvis, thigh, and shank during walking as well as the pelvis-thigh and thigh-shank coordination patterns in the frontal and horizontal planes during the stance phase between males and females. Compared to males, females had greater thigh adduction (p < 0.001) and internal rotation (p < 0.001) throughout the stance phase; significantly greater frequency of the pelvis-thigh anti-phase pattern in the frontal plane in the early (p = 0.002) and mid-stance (p = 0.003); and significantly greater thigh-shank anti-phase pattern in the frontal plane in the early (p = 0.001) and mid-stance (p = 0.015). These results suggest the presence of sex differences in the inter-segmental coordination of the pelvis and lower limb during walking. However, as this study could not determine a causal relationship between female sex and knee joint injury, further longitudinal studies are needed to determine the effects of differences in coordination patterns on the pathophysiology of the injury and pain generation.

Relationship Among 3 Different Core Stability Tests in Healthy Young Adults: Validity and Gender Differences.

CONTEXT: Core stability is important for preventing injury and improving performance. Although various tests for evaluating core stability have been reported to date, information on their relationship and the effect of gender differences is limited. This study aimed to (1) identify correlations among the 3 core stability tests and to examine the validity of each test and (2) identify gender differences in the test relationship and determine whether gender influenced test selection. DESIGN: Cross-sectional study. METHODS: Fifty-one healthy volunteers (27 men and 24 women) participated in the study. The participants underwent the following 3 tests: Sahrmann Core Stability Test (SCST), the lumbar spine motor control tests battery (MCBT), and Y Balance Test (YBT). Each parameter was analyzed according to all parameters and gender using the Spearman rank correlation coefficient. RESULTS: Overall, there was a strong positive correlation between SCST and MCBT and moderate positive correlations between SCST and YBT and between MCBT and YBT. Conversely, gender-specific analyses revealed no significant correlations between YBT and SCST and between YBT and MCBT in women, although significantly strong correlations were found among all tests in men. CONCLUSION: Although these 3 tests evaluated interrelated functions and may be valid as core stability tests, the results should be carefully interpreted when performing YBT in women.