A Rehabilitative Ultrasound Imaging Investigation of Lateral Abdominal Muscle Thickness in Healthy Aging Adults

Purpose: Rehabilitative ultrasound imaging (RUSI) is used to evaluate lateral abdominal muscle size and function during the abdominal drawing-in maneuver (ADIM), an exercise used to improve lumbar spine stability. Little is known about the size and performance of these muscles in healthy aging adults. The purpose of this study was to investigate, using RUSI, the size and symmetry of the lateral abdominal muscles bilaterally at rest and during the ADIM in healthy older adults and the reliability of these measurements. Methods: Three ultrasound images of the right and left lateral abdominal muscles were taken at rest and during the ADIM in 12 healthy older adults. Thickness of the transversus abdominis muscles (TrA), internal oblique (IO), and external oblique (EO) were measured for all images. Intraclass correlation coefficients were computed using model 3, form 1 (ICC3,1). Two ratios of the abdominal muscles were calculated in the relaxed and contracted states. Paired t-tests were used to compare relaxed muscle thickness to contracted muscle thickness for all 3 muscles for each side. To test further for interactions of side and contractile state, 2 x 2 repeated measures ANOVAs were performed. Side-to-side differences in absolute and relative thickness were assessed with paired t-tests for the TrA and IO muscles. Absolute and relative side-to-side muscle symmetry indices were computed for each muscle at rest. Results: There was a signi boxed times cant difference in muscle thickness between the contracted and relaxed states for both the TrA and IO. There was no signi boxed times cant difference between left/right muscle thickness for the TrA or IO at rest or during the ADIM. The TrA nearly doubled in size while thickness of the IO + EO stayed relatively constant during the ADIM. Reliability for absolute muscle thickness was generally excellent: ICCs3,1 ranged from 0.95 to 1.00 for intra-image reliability; 0.77 to 0.97 for inter-image reliability. Conclusions: These boxed times ndings support symmetrical and preferential activation of the TrA during the ADIM in healthy older adults. Continued research on the use of RUSI as a tool for both assessment and intervention in older adults is needed.