Interrater and Intrarater Reliability of Transverse Abdominal and Lumbar Multifidus Muscle Thickness in Subjects With and Without Low Back Pain

Study Design Two-group, repeated-measures reliability study. Objectives To determine interrater and intrarater reliability of ultrasound measurements of transverse abdominal (TrA) and lumbar multifidus (LM) muscle thickness, during rest and contraction, in subjects with low back pain (LBP) and healthy subjects over 3 consecutive days, performed by an experienced and a novice rater. Background Previous reliability studies of TrA or LM thickness did not simultaneously account for muscle state, rater experience, and multiday assessment in large subject samples. Methods The 2 raters measured TrA and LM thickness on 3 consecutive days in 42 healthy subjects and 56 subjects with LBP, during rest and contraction, and calculated the percent thickness change from rest to contraction. Intraclass correlation coefficients (ICC2,k) and 95% minimal detectable change in thickness were derived for a single measure (day 1) and an average measure (days 1–3). Results The interrater ICC2,1 values for single-measure thickness...