Effects of performing an abdominal hollowing exercise on trunk muscle activity during curl-up exercise on an unstable surface

[Purpose] The purpose of this study was to investigate the effects of the abdominal hollowing exercise on trunk muscle activity during the curl-up exercise on an unstable surface by measuring electromyography (EMG) activity. [Subjects] Fourteen young healthy adults (nine male, five female) voluntarily participated in this study. [Methods] Each subject was asked to perform a curl-up exercise on two supporting surfaces (stable and unstable surfaces) combined with the abdominal hollowing exercise on an unstable surface. The muscle activities of the rectus abdominis (RA), external oblique (EO), internal oblique (IO), and transverse abdominis (TrA) were measured using surface EMG during performance of the curl-up exercise. [Results] The EMG activity of the RA and EO was significantly higher on an unstable surface than on a stable surface during the curl-up exercise. The EMG activities of the TrA and IO were greater in combination with the abdominal hollowing exercise on an unstable surface than during the curl-up exercise on both a stable and unstable surface. [Conclusion] These findings suggest that the local trunk muscle activity during the curl-up exercise is more strongly affected by combination with the abdominal hollowing exercise than by performance on an unstable supporting surface.