Loss of muscle strength and power in older women and adaptation to resistance training
The studies described in this thesis aimed to examine some of the mechanisms underlying the lower levels of muscle strength and power in older women, who are at higher risk than men for age-related disability, and some of the adaptations in response to resistance training. The initial study showed that it is not only a smaller contractile muscle volume, estimated separately from the intramuscular non-contractile tissue, which accounts for differences in quadriceps muscle strength, expressed as torque, between young and older women, but also a higher level of coactivation of the antagonist muscles. Lower limb explosive power, which depends on both strength and speed of movement, and is more predictive of functional difficulties than strength per se, was then compared between young and older women during a single leg-press action after optimisation of load. The older women could not even move the resistance at which the young women achieved maximum power. Their lower levels of power, which appear to be more affected by ageing than isometric strength, were due to lower levels of both force and velocity at which maximum power was measured. In the third study, the neural adaptations to a short-term resistance-training programme were investigated by analysing the time and frequency-domain characteristics of the surface electromyogram measuredo n the biceps-brachii muscle during constant-force sustained-isometric contractions. Older women responded to the same training programme with a lower increase in strength than the young women. This was accompanied by a different electromyographic response in the two groups. Finally, three modalities of resistance-training, which were carried out for 16 weeks on a cycle-ergometer at either high-resistance and low-speed, low-resistance and high-speed, or a combination of both, were shown to be equally effective in improving power, strength and selected functional abilities in a healthy population of 65-74 year-old women. The findings of these studies are discussed in relation to the current knowledge on mechanisms and adaptations of muscle strength and power in the older woman.