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[Purpose] To study the activities of the deep abdominal muscles during trunk rotation using ultrasound imaging. [Subjects] The subjects were 10 healthy persons with no lower limb or trunk disorders, and 6 chronic low back pain (LBP) patients. [Methods] In the sitting position, trunk rotation was performed voluntarily, and passively with a device. The thickness changes in the transversus abdominis (TrA) during performance of the task were compared between the healthy subjects and LBP patients. [Results] We found that the TrA thickness increased unilaterally in trunk rotational movement of the healthy subjects, but not in the LBP patients. [Conclusion] The difference observed in the TrA activities of healthy subjects and LBP patients suggests TrA contributes to trunk rotation, and TrA functionality is one aspect of the difference between healthy subjects and LBP patients. [ABSTRACT FROM AUTHOR]

[Purpose] The purpose of this study was to investigate the effect of the amplitude and velocity on the weight shift task. [Subjects] Six healthy young adults participated. [Method] The visually-guided weight shift task was performed on one force platform. Motor directions were the anteroposterior and mediolateral directions, load amplitudes were 50 N and 1/3 of subject's weight, and motor frequencies were 0.1-1.0 Hz. The spatial and temporal errors were analyzed to assess the motor performance. [Results] There was no significant difference between motor directions. The spatial errors for the light weight were larger than those for the heavy weight. The temporal errors were not affected by load amplitudes and increased with increases in motor frequency. [Conclusion] During the weight shift task, spatial and temporal controls were affected by the load amplitude and the motor frequency, respectively. Balance exercise with this task should be reconsidered in clinical settings. [ABSTRACT FROM AUTHOR]