Abdominal muscle activity during abdominal hollowing in four starting positions.

The aim of this study was to investigate the activity of the rectus abdominis (RA), external abdominal oblique (EO), and transversus abdominis/internal abdominal oblique (TrA/IO) muscles during abdominal hollowing (AH) in four positions: crook lying, prone lying, four-point kneeling, and wall support standing. Thirty-two healthy participants, aged 21.3+/-0.8 years were recruited. They were instructed to perform maximal voluntary contraction (MVC) and AH. The electromyography (EMG) data of each muscle during AH were normalized as a percentage of MVC. During AH in all four starting positions, significant differences were found in the EMG activity of RA, EO, and TrA/IO (p<0.001). The TrA/IO exhibited the highest while the RA exhibited the lowest EMG activity. Among the four different starting positions, only the TrA/IO showed significant difference in mean EMG activity (p<0.001). The results suggest that all four starting positions can facilitate TrA/IO activity with minimal activity from RA and EO.