Age-Related Differences in Coupling of Toe and Center of Pressure during the One-Legged Stance

This study aimed to investigate the characteristics of the coupling of the center of pressure (COP) movement and toes in older adults during one-legged standing (OLS). Participants were community dwelling older and younger adults. Toe vertical force during the OLS was recorded using a plantar-pressure distribution system, and the vertical forces in the hallux, little toe, and the first and fifth metatarsophalangeal (MP) joints were analyzed. A cross-correlation function was performed to examine the coordination between toes and between COP movement and four regions of the foot. The cross-correlation functions showed no significant difference in coefficients between toes. The OLS duration in the older adults was significantly correlated with the coefficient between the medial-lateral component of the COP and the first MP region. This study suggests that it is important to press the first MP region appropriately relative to COP movement to maintain the OLS.

Joint Coordination Organizes to Form the Task-Dependent Trajectory of the Body Center of Mass

As the central nervous system controls whole-body motion, which involves multi-joint movement, certain problems with regard to the number of variables controlled by the central nervous system arise (i.e., the “degree of freedom problem”). The central nervous system solves these problems not by controlling joint movements, but rather by controlling only the task-dependent center of mass (COM) position of the whole body. Although uncontrolled joint movement should be organized in a coordinate manner to form the task-dependent COM position, it is unclear what kind of law joint coordination is organized by. Hence, in the present study, we aim to clarify the shape of joint coordination by elucidating the mutual relationship between the COM trajectory and joint movement during whole-body motion. Downward squatting motions with five trunk angles are recorded by using a 3-D motion analysis system in 8 healthy males. The COM trajectory shows a task-dependent path in all trunk conditions. The shank angle decreases with an increase in the trunk angle to produce the task-dependent COM trajectory, whereas the thigh showsd a constant angle. These findings demonstrate that the COM trajectory is constrained by biomechanical dynamics and minimum muscle torques, and that the joints are organized into a lawful coordinative structure to form the COM trajectory.

Autism-Spectrum Quotient Is Associated with Observational Skill Acquisition in Healthy Young Adults

Although observational motor learning is one method of skill acquisition, this type of motor learning is not equally effective for all individuals. To clarify factors associated with the effectiveness of motor learning, we examined the association between model-observational skill acquisition and the Autism-Spectrum Quotient (AQ), which is reportedly associated with motor learning via visual information. Twenty healthy adults performed the Kendama task. The participants practiced under three conditions: using their own methods (self), following observation of model actions (model-observation), and following observation of their own actions (self-observation). Measurement trials were performed 20 times prior to self-practice sessions and after each practice session. Success ratios were calculated for each measurement trial. All participants completed the AQ. The difference in success ratios for measurement sessions following practices between the self and model-observation conditions was significantly negatively correlated with AQ scores. Individuals with low AQ values can more easily acquire skills via model-observational motor learning than those with relatively higher AQ values.