Measuring muscle size and symmetry in healthy adult males using a time-efficient analysis of magnetic resonance images

Objective: Muscle volume (MV) analysis from magnetic resonance imaging (MRI) is time-intensive, and limited measurement reliability data are available. This study investigated a method to reduce lower limb MV analysis time demands, established reliability of these measurements, and applied the findings to quantify muscle size and symmetry in healthy adult males. Approach: Bilateral MRI images were acquired from 15 healthy males (age: 26.5 ±4.6 years, height: 1.81 ±0.09 m, body mass: 80.4 ±12.4 kg) for the entire lower limb. In two participants, the individual gluteals, quadriceps, hamstrings, and triceps surae were manually outlined every 5 mm and MV calculated using 5, 10, 15, 20, 25, and 30 mm distances between images to determine an appropriate distance for reducing analysis time. For all 15 participants, 35 muscles in each limb were manually outlined every 15 mm for use in MV calculations. Reliability of muscle cross-sectional area (CSA) measurements was determined within- and between-sessions and MV measurement reliability determined between-sessions. Between-limb symmetry was calculated using symmetry indices. Main results: A 15 mm inter-slice distance was appropriate for measuring MV (mean difference compared to reference method: 0.7 ±0.7%). Between-session measurement reliability was good for MV (Typical Error preferred kicking limb (TEP): 1.2%, nonpreferred kicking limb (TENP): 0.8%) and CSA (TEP: 3.4 ±2.9%, TENP: 3.2 ±1.9%) although CSA typical error was larger with increased between-session time (TEP: 4.1 ±3.1%, TENP: 4.7 ±4.0%). Between-limb differences in MV were small (mean symmetry index: 0.4 ±4.1%). Absolute differences in individual MV were larger (mean: 12.6 ±2.6%), but representing muscles as functional anatomical groups showed smaller absolute between-limb differences (mean: 4.7 ±1.8%). Significance: MV analysis time demand can be reduced by increasing the distance between analysed MRI slices, although participant height, muscle length and shape require consideration. Minimal between-limb muscle size differences have been reported in adult males.