A ssessment of function of the deep abdominal musculature in the laboratory has largely used methodologies such as functional movement tasks and fine-wire electromyography (EMG). 13,10,11,15,27 While fine-wire EMG is primarily restricted to laboratory research, rehabilitative ultrasound imaging (RUSI) offers a noninvasive and simpler method of assessing deep lumbopelvic muscle function. Recent work has shown that measures of transversus abdominis (TrA) muscle contraction, 20 internal oblique (IO) muscle contraction, and length of the TrA muscle obtained using RUSI correlated well with measures obtained by fine-wire EMG for isometric contractions of these muscles. 12,20 For increases in thickness of the TrA and IO muscles and changes in length of the TrA muscle (measured as lateral displacement of the fascial insertion of the TrA muscle) there were consistent, clear changes in sonographic parameters, with incremental changes for contractions of less than 20% of maximal voluntary contraction (MVC).Clinical muscle testing of the TrA muscle has been based on its anatomical structure and horizontal fiber arrangement. Two muscle tests include observation of the abdominal wall during either a voluntary drawing-in of the abdominal wall 26 or by using automatic responses of the muscle to expiration.18 A relationship between the clinical muscle test and laboratory EMG measures of TrA muscle function has been demonstrated.14 In addition, the action of the bilateral muscle bellies of the TrA muscle has been viewed during the drawing-in maneuver using RUSI and magnetic resonance imaging (MRI). 8,9 In a recent study conducted on elite asymptomatic cricketers, 9 the muscle bellies of the TrA muscle were seen to thicken as well as shorten in length durt sTudy design: Test-retest intrarater reliability study.t oBJecTive: To examine reliability of abdominal musculature measurements across a broad range of conditions for a physical therapist newly trained in assessment using rehabilitative ultrasound imaging (RUSI).t BAckground: RUSI has previously been used to assess abdominal muscle function during a drawing-in maneuver of the anterior abdominal wall, and measurements conducted by an experienced assessor have been validated by comparison with magnetic resonance imaging. Few studies have examined the reliability of less experienced operators, and only in isolated measurement conditions. t MeTHods And MeAsures: Nineteen subjects (11 female, 8 male) without a history of low back pain performed the abdominal drawing-in maneuver in a supine hook-lying position. RUSI was used bilaterally to assess the thickness of the internal oblique (IO) and transversus abdominis (TrA) muscles at rest and on contraction, as well as changes in the length of the TrA muscle (indicated by slide of the anterior abdominal fascia). The reliability of a novice rater who received 8 hours of training was examined (a) across 3 measurements of the same ultrasound image, (b) across 3 separate ultrasound images (averaged for days and sides of abdomen), and (c) ac...