Intra-rater Reliability of B-Mode Ultrasound Imaging of the Abdominal Muscles in Healthy Adolescents During the Active Straight Leg Raise Test

Background: To date, the reliability of ultrasound imaging (USI) measures of the abdominal muscles in children and adolescents during the active straight leg raise (ASLR) test has not been confirmed. Objective: To assess the intra-rater reliability of USI measures of the thickness and percentage thickness change of the external oblique (EO), internal oblique (IO), and transversus abdominis (TrA) on both sides of the body during the ASLR test in healthy adolescents. Design: Single-group repeated-measures intra-rater reliability study. Setting: School. Participants: Thirty-nine adolescents between the ages of 13 and 16 years. Methods: Three repeated USI measurements were recorded in the supine resting position and during the ASLR test at 2 sessions, 6 to 8 days apart. In the supine position, measurements were collected at the end of normal expiration. In the case of ASLR, measurements were collected when the person undergoing examination touched the transverse delimiter with the distal part of their lower leg, that is, to a 30 degrees flexion of the hip. Main Outcome Measurements: USI of abdominal muscle thickness. Results: By using the mean of 3 measures in the supine, resting position, intra-examiner reliability point estimates (intraclass correlation coefficient [ICC](3.3)) ranged from 0.95 to 0.97 for EO, IO, and TrA. During the ASLR test, the ICC result of thickness measurements of all muscles was also above 0.90. In terms of percentage change of muscle thickness, the highest ICC3.3 result obtained for the TrA was 0.81-0.85; for EO the result ranged from 0.72-0.89, and the result for the IO was between 0.65 and 0.79. Conclusion: USI measurements of the thickness of the EO, IO, and TrA muscles at rest and during the ASLR test in healthy adolescents between 13 and 16 years of age are reliable. Because of an increase in the precision of measurements, we recommend using the mean of 3 consecutive measurements of the EO, IO, and TrA muscles in adolescents to ensure a good reliability level. Based on 3 consecutive measurements, good reliability for the percentage change in the TrA thickness was achieved.