Reliability of real-time ultrasound for measuring skeletal muscle size in human limbs in vivo: a systematic review

Objective: To systematically review evidence for the reliability of real-time brightness-mode ultrasound for assessing skeletal muscle size in human limbs in vivo and to establish in which populations and anatomical sites the reliability had been tested. Data sources: Articles were retrieved via electronic database searching and expert contact. Study selection: Studies reporting reliability indices of test-retest measures of real-time brightness-mode ultrasound measures of skeletal muscle size within human limbs were included. Data extraction: Articles were assessed for methodological quality by two reviewers, decisions were made by consensus. Participant characteristics, measurement protocol, ultrasound protocol, type of reliability measured and statistical methods were extracted by one reviewer. Data synthesis: Twenty-four articles were included, involving 605 participants. Studies were of low to moderate methodological quality. Most studies were conducted within the healthy population. Only one study demonstrated poor reliability at one site only, and only when the participants were measured in the supine position. Conclusion: There is a moderate amount of low-level evidence that real-time brightness-mode ultrasound has good reliability for measuring muscle size across a number of limb sites in healthy populations. There is limited evidence for the reliability of ultrasound measures of muscle size in clinical populations.