Age-related differences in rate of power development exceed differences in peak power

Peak power (pP) declines during aging, resulting in reduced functional performance. However, the rate of power development (RPD) takes into account the short response times available during many functional tasks and may therefore add valuable information to functional declines. This study examined the age-related effects on pP and RPD of the knee-extensors across different loads and how these are related to functional performance. 36 young (male 21, female 15, age = 22 +/- 2 years) and 56 older adults (male 26, female 30, age= 68 +/- 5 years) performed four maximal isotonic contractions against three loads (40, 20 and 60% of maximal isometric strength) on a Biodex System 3 dynamometer. pP was calculated as the highest value and RPD as the linear slope of the power-time curve. Functional performance in the older group was tested by 7.5-meter fast walk, timed up-and-go and stair climbing. pP and RPD were higher in young compared to old and this was more pronounced with lower loads. Agerelated differences in RPD (range from 37 to 44% across loads) were higher than in pP (24-37%). Both pP and RPD showed a positive correlation with functional performance (r: 0.59-0.64). To conclude, percent differences in RPD exceed differences in pP between young and old. This emphasizes the inability to generate power rapidly at older age and underlines the importance of time-dependent measures to detect age-related changes in muscle function.