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.

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.

Effects of core stability on shoulder and spine kinematics during upper limb elevation: A sex-specific analysis.

BACKGROUND: Upper limb elevation begins with core stabilization, but the effects of core stability on shoulder and spine kinematics are unknown. Sex differences also exist in shoulder kinematics and core stability. OBJECTIVE: To clarify the effects of core stability on shoulder and spine kinematics during upper limb elevation by taking sex into account. DESIGN: Cross-sectional. METHODS: The Sahrmann Core Stability Test, lumbar spine motor control test battery, and Y Balance Test (lower and upper quarters) were performed in 50 healthy young adults. For each test, a principal component (PC) analysis was conducted according to sex; the overall core stability score was calculated. The top and bottom third of the PC scores were defined as high and low score groups, respectively (each group: nine males and eight females). Shoulder and spine kinematics during upper limb elevation were compared separately for males and females. RESULTS: Spinal extension was greater in the low score group by a maximum of 1.9° in males (P < .001; η2 = 0.068) and 1.6° in females (P < .001; η2 = 0.141). In the low score group of females, the scapular posterior tilt was a maximum of 5.6° smaller (P < .001; η2 = 0.221) and glenohumeral elevation was a maximum of 4.5° larger (P < .001; η2 = 0.113) than the high score group of females. CONCLUSION: Core stability affected spine and female scapular and glenohumeral kinematics during upper limb elevation. Core stability may be one of the potential contributors to shoulder kinematics, particularly in females.

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.