[Purpose] We investigated the characteristics of electromyographic trunk muscle activities and the relationship between the trunk muscle activities and postural sway during one-leg standing.[Subjects] Ten people (25.1 ± 4.4 years old) participated in this study.[Methods] Electromyographic trunk muscle activities and postural sway were evaluated during one-leg standing and twoleg standing.[Results] Thoracic and lumbar erector spinae and external oblique on the side of the raised leg were activated significantly more higher in one-leg standing than in two-leg standing. Lumbar multifidus and internal oblique on the side of standing leg had a tendency to be activated higher in one-leg standing. After some trunk muscle activities on the side of the raised leg and postural sway correlated significantly.[Conclusion] The results suggest that trunk muscle activities influence the balance ability during one-leg standing.

[Purpose] We investigated the characteristics of electromyographic trunk muscle activities and the relationship between the trunk muscle activities and postural sway during unstable sitting.[Subjects] Ten people (25.1 ± 4.4 years old) participated in this study.[Methods] Electromyographic trunk muscle activities and postural sway were evaluated during unstable sitting and stable sitting.[Results] Abdominal muscles were activated significantly more higher in unstable sitting than in stable sitting. Also, rectus abdominis, thoracic and lumbar erector spinae muscles activities that could be classified as global muscle activity and postural sway correlated significantly, but local muscle activity did not. [Conclusion] The results suggest that rectus abdominis, thoracic and lumbar erector spinae muscle activities that can be classified as global muscle activity influence the balance ability during unstable sitting.

We examined the effect of trunk exercise for prevention of low back pain on trunk back muscle endurance of elderly people. [Subjects] Twenty-four people (74  5.1 years old) participated in this study. They were assigned to an exercise group or a control group. [Methods] The endurance parameters included the holding time of the Trunk Holding Test (THT) and electromyographic fatigability (IMF, MF-Slope) was also evaluated. [Results] Although a significant change in electromyographic fatigability was not observed after eight weeks of exercise in either group, THT increased significantly only in the exercise group. [Conclusion] The results suggest that the exercises conducted in this study were effective for improvement of THT that is one of the risk factors for low back pain.