Ageing is not associated with a decline in neuromuscular innervation or reduced specific force in men aged 20 and 50 years

The exact mechanisms responsible for the decline in strength with age are y et to be completely elucidated. Three proposed mechanisms responsible for t he detrimental effect of increasing age on strength include changes in musc le mass, specific force and/or neuromuscular innervation. Thus, the purpose of this investigation was to determine if the age-related reduction in pea k isometric strength was primarily associated with changes in muscle cross- sectional area, neuromuscular innervation and/or specific force. The cross- sectional area of the knee extensor muscles (QCSA) was estimated in 13 youn ger men (YM; 20.8 +/- 1.6 years) and eight middle-aged men (MM; 53.8 +/- 4. 2 years) prior to performing a series of four maximal voluntary isometric c ontractions on an isokinetic dynamometer at an angle of 60 degrees knee fle xion. Peak force was determined and surface electromyography was sampled fr om the rectus femoris muscle during each maximal voluntary contraction. The cross-sectional area of the knee extensor muscles, peak force and integrat ed electromyography (IEMG) were significantly lower in the MM (P<0.01). How ever, when peak force and peak IEMG values were corrected for QCSA, there w ere no significant differences between age groups. These results suggest th at the reduction in peak isometric force observed in the MM was primarily a ssociated with quantitative changes in muscle mass, rather than reduced neu ro-muscular innervation or specific force. Therefore, preserving muscle mas s through resistance training may significantly reduce the age-associated d ifferences in peak strength and assist in promoting quality of life and fun ctional independence in older adults.