Age- and sex-dependence of muscle quality: Influence of intramuscular non-contractile tissues

Purpose: Muscle quality is explained by the ratio between muscle size and strength. Conventionally, muscle size is evaluated without considering the composition of contractile and non-contractile tissues in muscle, hence the influence of non-contractile tissues on muscle quality is not fully understood, especially within aging muscle. This study investigated the differences in intramuscular non-contractile tissues between different age and sex groups, and investigated their influence on muscle quality. Methods: Eighty-two older and 64 young females and males participated. Muscle cross-sectional area (quadriceps and hamstrings), separating contractile and non-contractile areas, was calculated from the magnetic resonance image of the right mid-thigh. Maximal voluntary isometric knee extension and flexion torque was measured. Torque/muscle area and torque/contractile area were calculated for each age and sex group. Results: Non-contractile/muscle area was higher in older than in young individuals in both muscle groups (p females) (p