Test-retest reliability of measurements of abdominal and multifidus muscles using ultrasound imaging in adults aged 50-79 years.

Test-retest reliability of the combined process of ultrasound imaging (USI) and image measurement of thickness of abdominal and upper lumbar multifidus (MF) muscles and MF cross sectional area (CSA) of older adults has not been established. Imaging muscles of older adults can be challenging due to age-related changes in the spine and skeletal muscle so establishing test-retest reliability in this population is important. This study aimed to evaluate test-retest reliability of USI of abdominal and MF muscle thickness and MF CSA for adults aged 50-79 years. One operator took single sets of ultrasound images of abdominal and MF muscles of 23 adults aged 50-79 years participating in a clinical trial of vitamin D supplementation for knee osteoarthritis, on two occasions, one week apart. Images were subsequently measured by a single examiner. Test-retest reliability for abdominal muscle thickness and MF CSA was substantial (intraclass correlation coefficients (ICC) > 0.81) and for MF thickness ranged from fair to substantial (ICC 0.55-0.86). The standard error of measurement (SEM) was low (0.02-0.21) in every case. ICCs were low and SEM values were high for percentage thickness change. The substantial test-retest reliability of abdominal and MF (L4-L5) muscle thickness and of MF CSA supports the use of USI as a clinical and research tool to assess abdominal and MF muscle thickness and MF CSA of older adults.