No abstract

Context: Excessive hip adduction and internal rotation are abnormal movements that may lead to the onset and progression of patellofemoral pain. Previous studies have reported that lower dynamic frontal plane hip joint stiffness in the gait of women is associated with the magnitude of hip adduction and internal rotation angles. However, the factors contributing to the lack of dynamic frontal plane hip joint stiffness in the gait of young women are unclear. This study aims to investigate the factors affecting dynamic frontal plane hip joint stiffness during the weight-acceptance phase of the gait of healthy young women. Design: Cross-sectional study. Methods: This study included 30 healthy women between the ages of 18 and 30 years. The pelvic width/femur length ratio was calculated by dividing the pelvic width by the femur length. Data on hip kinematics and kinetics and activation of the gluteus maximus and medius, tensor fasciae latae, and adductor longus muscles during gait were collected using a motion capture system, force plates, and surface electromyography. Stepwise multiple regression analysis was conducted to determine the extent to which each independent factor affected dynamic frontal plane hip joint stiffness. Results: In healthy young women, decreased dynamic frontal plane hip joint stiffness was associated with decreased muscle activity of the gluteus maximus during the gait, as well as greater pelvic width/femur length ratio. Conclusions: Women with a relatively great pelvic width relative to femur length may have more difficulty in producing dynamic frontal plane hip joint stiffness. However, increasing the muscle activity of the gluteus maximus may contribute to increased dynamic frontal plane hip joint stiffness.

Scapular dyskinesis results from weakness of the lower trapezius and serratus anterior, but no studies have investigated the motor unit (MU) behavior required for muscle exertion. This study aimed to classify scapular dyskinesis into raising (SDR) and lowering (SDL) phases and investigated the MU behaviors of the lower trapezius and serratus anterior. Fifty healthy young subjects underwent a scapular dyskinesis test and were divided into Normal, SDR, and SDL groups. The subjects performed submaximal voluntary contractions of the lower trapezius and serratus anterior, and surface electromyography signals were decomposed into the MU action potential amplitude (MUAPAMP), mean firing rate (MFR), and recruitment threshold (RT). The average MUAPAMP and MFR and the slopes and y-intercepts of the linear MUAPAMP-RT and MFR-RT were compared. The MUAPAMP-RT slopes in the lower trapezius (p = 0.049, r = 0.420) and serratus anterior were smaller (p = 0.010, r = 0.490) and the MFR-RT y-intercept in the serratus anterior was lower (p = 0.004, r = 0.540) in the SDR group than in the Normal group. Differences in other parameters between the SDL and Normal groups were not significant. Lower trapezius and serratus anterior MU behavioral changes may cause scapular dyskinesis in the raising phase.