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.