The heterogeneity of age-related muscle atrophy of lower limb muscles

Age-related skeletal muscle atrophy differs between upper and lower body muscles and may also differ between lower limb muscles, but these muscle-specific patterns remain poorly characterised. We acquired axial 3T magnetic resonance images from sex-balanced samples of thirty young (24+/-4 years) and thirty older adults (73+/-4 years). Muscle volume of seventeen lower limb muscles/compartments was quantified using manual segmentation and expressed as absolute volume, relative to body mass, and as a percentage of total muscle volume. Absolute muscle volume was lower in older adults in 13 out of 17 muscles compared to young, with substantial heterogeneity in the effect sizes (d=0.01-3.36). Age group * muscle interaction contrasts revealed muscle-specific age-related differences in volume. Three of the quadriceps muscles demonstrated greater age-related atrophy compared to several other muscles (e.g. vastus lateralis differing from 14 of the other 16 muscles; d[≥]1.54). Conversely, the anterior and deep posterior compartments of the shank and biceps femoris short head showed significantly smaller age-related atrophy than several other muscles. These interaction effects were exacerbated when expressed in relative terms. Consequently, three of four shank compartments, gluteus maximus and adductor magnus represented a greater proportion of total muscle volume in older adults, whereas the vastus lateralis, vastus intermedius, rectus femoris, semitendinosus, gracilis, and iliopsoas contributed a smaller proportion in older adults. These findings highlight the variability in age-related leg muscle atrophy in a large mixed sex cohort, resulting in a redistribution of muscle volume in the lower limb.