Rate of power development of the knee extensors across the adult life span: A cross-sectional study in 1387 Flemish Caucasians

A growing body of research in elderly populations suggests that the early phase of an explosive muscle contraction (i.e., <= 200 ms) may be more functionally relevant than peak values. However, age-related variation in early phase explosive strength has never been investigated across the full-adult life span. This cross-sectional study investigated the age-related changes in the rate of power development (RPD) and compared it to the changes in peak power (P-peak), both in terms of magnitude and onset, across the adult life span. Age-related declines in power and determinants of muscle power were compared between sexes. 1387 adults (male 813, female 574), aged 18-78 years, performed three maximal isoinertial knee extensor tests at 20% of their isometric maximum on a Biodex dynamometer. P-peak was calculated as the highest value and RPD as the linear slope of the power-time curve. Velocity (v) and torque (T) at P-peak were registered. In both men and women, the decline in P-peak and RPD was already apparent from 40 years onwards. Annual percent decline rates were greater for RPD (-1.1% for men and - 1.3% for women) than P-peak - 0.9% for men and - 1.0% for women). Velocity at P-peak showed the lowest annual percent decline rates (- 0.3% for men and - 0.4% for women). Men performed better than women on all parameters (all p < 0.001). Velocity at P-peak tended to decline more in women than in men (p = 0.065). To conclude, both knee extensor P-peak and RPD can be used to screen for age-related neuromuscular weaknesses at an early age. Both sexes seem equally susceptible to age-related declines in knee extensor power. In addition to traditional slow-speed resistance exercise, prevention strategies should include explosive exercises. Explosive exercises may be especially relevant in women, considering that they tend to decline more in the velocity component of muscle power.