Comparison of changes in abdominal muscle thickness between standing and crook lying during active abdominal hollowing using ultrasound imaging.

To determine if transversus abdominis (TrA) demonstrates a greater increase in thickness on lower abdominal hollowing (LAH) in standing compared to crook lying. Muscle thickness measurements of TrA, addition of internal obliques (IO) and external obliques (EO) were measured using ultrasound imaging at rest and during LAH on 28 healthy controls (14 female, 14 male) in crook lying and standing. TrA demonstrated greater thickness changes on LAH in standing (+0.88 mm+/-0.12 mm). IO and EO demonstrated greater thickness changes on LAH in crook lying (+0.59 mm+/-0.08 mm and -0.87 mm+/-0.12 mm, respectively). These differences were all significant (p<0.001). Increased resting thickness was noted in standing in TrA (20.7%), IO (10.3%) and EO (1.2%). This increase was only significantly different between TrA and EO (P=0.004). TrA showed significantly greater increases in thickness on LAH in standing compared to crook lying, and with greater specificity in relation to IO and maybe EO. If muscle thickness can be an indicator of muscle function or activity, then this suggests that TrA rehabilitation should be facilitated in positions of greater function, such as standing.