Effects of age and sex on neuromuscular-mechanical determinants of muscle strength

Abstract

The aim of this study was to concurrently assess the effect of age on neuromuscular and mechanical properties in 24 young (23.6±3.7years) and 20 older (66.5±3.8years) healthy males and females. Maximal strength of knee extensors (KE) and flexors (KF), contractile rate of torque development (RTD) and neural activation of agonist-antagonist muscles (surface EMG) were examined during maximal voluntary isometric contraction (MVIC). Tissue stiffness (i.e. musculo-articular stiffness (MAS) and muscle stiffness (MS)) was examined via the free-oscillation technique, whereas muscle architecture (MA) of the vastus lateralis and subcutaneous fat were measured by ultrasonography. Males exhibited a greater age-related decline for KE (47.4%) and KF (53.1%) MVIC, and RTD (60.4%) when compared to females (32.9, 42.6 and 34.0%, respectively). Neural activation of agonist muscles during KE MVIC falls markedly with ageing; however, no age and sex effects were observed in the antagonist co-activation. MAS and MS were lower in elderly compared with young participants and in females compared with males. Regarding MA, main effects for age (young 23.0±3.3 vs older 19.5±2.0mm) and sex (males 22.4±3.5 vs females 20.4±2.7mm) were detected in muscle thickness. For fascicle length, there was an effect of age (young 104.6±8.8 vs older 89.8±10.5mm), while for pennation angle, there was an effect of sex (males 13.3±2.4 vs females 11.5±1.7°). These findings suggest that both neuromuscular and mechanical declines are important contributors to the age-related loss of muscle strength/function but with some peculiar sex-related differences.