Combined Effects of Ageing and Body Composition on Skeletal Muscle Structure and Function in Untrained Individuals

This thesis investigated whether body composition modulates neural, morphologic and/or functional characteristics of skeletal muscle in young (Y: 18-49 years) and old (O: 50-80 years), adult male (n=34) and female (n=102) populations. Classification by BMI revealed no significant differences in agonist muscle activation and antagonist co-contraction in Y and O individuals. However, high adiposity in Y (but not O) females led to lower muscle activation (94 vs. 88 %). Plantar flexion (PF) maximum voluntary contraction torque corrected for antagonist co-contraction and muscle activation (nMVC), gastrocnemius medialis (GM) muscle volume (MV) and physiological cross sectional area were significantly higher in the Y obese compared with that of underweight (+27%, +77% & +77%) and normal weight (+23%, +73% & +70%) females. No group differences were reported in the O female cohort. Fascicle pennation angle in Y and O females incremented with increasing BMI. PF nMVC normalised to GM MV (nMVC/GM MV) was lower in the Y obese females whether classified by BMI (-26%) or adiposity (-11%) in comparison to their normal weight counterparts. At the fascicular level, no impact of BMI or adiposity was evident in either Y or O female populations. There was an ageing-associated accelerated loss of muscle content in the obese (-2.1cm3/year) and high adipose (-2.1cm3/year) females. The continuum of both adiposity and BMI revealed similar impact on nMVC, GM MV and nMVC/GM MV, in both Y and O males. Interestingly, the slopes of the regressions implied the Y males to increase GM specific force (SF) with either increasing BMI or adiposity. Differential gender effects were observed at the fascicular level with the slope of GM SF being steeper in the obese males compared with the obese females (-0.373 N/cm2/year vs. 0.056 N/cm2/year; Student’s t-statistic -4.56, p