Transversus abdominis: changes in thickness during an incremental upper limb exercise test.

The aim of this study was to measure transversus abdominis (TrA) during an incremental fatiguing task. Using real-time ultrasound, TrA thickness was measured in 26 healthy subjects (18-25 years, 9 male) during an unsupported upper limb exercise test (UULEX). Repeatability of changes in TrA thickness during the UULEX was established by using a test-retest process (n=9, intraclass correlation coefficient=0.62 (95% CI 0.38-0.82), standard error of measurement approximately 1 (95% CI 0.87-1.08)). Using mixed model analysis with time as an independent variable, TrA thickness changed significantly throughout the UULEX (p < 0.05). Measures of TrA thickness at minutes 10, 11, and 12 were significantly greater than at baseline (p=0.006 (95% CI 0.23-1.35), 0.001 (95% CI 0.45-1.61), and <0.0001 (95% CI 0.77-2.03), respectively). Transversus abdominis was shown to be continuously and increasingly active over the 12 minutes of an incremental bilateral upper limb test in young healthy adults. As increases in TrA thickness occurred at the points of greatest postural and ventilatory demands, these findings may have implications for subjects with musculoskeletal or respiratory impairments who are often challenged by upper limb tasks.