Reliability of Ultrasound Imaging Measures of Transverse Abdominis and Lumbar Multifidus in Various Positions

Objective: To determine the reliability of measurement of muscle activation via ultrasound imaging measures of the transverse abdominis (TrA) and lumbar multifidus (LM) in tabletop, seated, standing, and walking conditions. Design: Descriptive laboratory study. Setting: University research laboratory. Participants: Sixteen healthy participants (age, 20.4 +/- 1.8 years; height, 167.7 +/- 9.0 cm; mass, 65.1 +/- 10.8 kg). Interventions: None. Main Outcome Measurements: The activation ratio (AR) of TrA and LM and preferential activation ratio of TrA in tabletop, seated, standing, and walking positions were assessed by the same examiner during 2 ultrasound imaging sessions 24-72 hours apart. Statistical analysis included determination of intraclass correlation coefficients (ICCs) using analysis of variance for each muscle and position between sessions. Results: Excellent reliability was found in TrA AR between sessions for healthy participants in the tabletop position (ICC3, k = 0.903), and acceptable to excellent reliability was found in seated (ICC3, k = 0.613), standing (ICC3, k = 0.553), and walking (ICC3, k = 0.737) positions. LM AR was fair in the tabletop position for these participants (ICC3, k = 0.264). The preferential activation ratio for healthy participants was substantially reliable in tabletop and seated positions (ICC3, k = 0.668, 0.684) and showed fair reliability for walking (ICC3, k =0.455). Conclusions: Ultrasound imaging is a reliable method of measuring muscle thickness across multiple positions in healthy persons. This measure may be used to compare abdominal muscle thickness across populations or after interventions. LM AR was only found to be reliable in the tabletop position.