Comparison between young and older women in explosive power output and its determinants during a single leg-press action after optimisation of load.

Lower limb explosive power, which is more predictive of functional difficulties than strength per se with women being more at risk than men for disability, has been previously compared between young and older women using systems with fixed inertia. Individuals may have been obliged to use a percentage of their maximum strength that is not ideal for performing the movement at the optimum speed for maximum power output. This study was designed to compare explosive power output and its two determinants, optimal force and optimal speed, during a leg-press action between young and older women after optimising the load for maximum power production. The experiments were carried out on 20 women in good physical condition: 10 older, aged between 65 and 74 years and 10 young, aged between 18 and 30. Explosive power output was measured by setting the initial load at different percentages of maximum isometric strength and measuring the corresponding speed of movement during a leg-press action of the dominant leg. Maximum peak power, which was obtained at 60% of maximum isometric strength in both young and older women, was 61% lower in the older women ( P<0.0001). This was due to a 52% lower optimal force ( P<0.0001) and 21% lower optimal speed ( P<0.01). The ratio of peak power to maximum isometric strength was 22.1% lower in the older women ( P<0.01). After optimising the load, both lower speed of movement and lower strength determine the lower levels of power in older women. Power is more affected by ageing than isometric strength.