The ability to develop adequate quadriceps muscle power may be highly predictive of subsequent disability among older persons. Rate as well as quantitative (sarcopenia) and qualitative (among other slowing of muscles) contributors to that age-related power decline are poorly known. The relationship of quadriceps maximal short-term power (P(max)) and corresponding optimal shortening velocity (upsilon(opt)) with age was assessed in 335 healthy men aged 23-88 years. The P(max) and upsilon(opt) were measured on a friction loaded non-isokinetic cycle ergometer. Anthropometric dimensions were used to estimate lean thigh volume (LTVest) and quadriceps mass. The decline in P(max) across the adult life span (10.7% per decade) was greater than the usually reported decrease in maximal muscle strength. Power decreased already after the fourth decade. Both muscle mass (4.1% decline for LTVest or 3.4% for quadriceps mass per decade) and upsilon(opt) (6.6% decline per decade) contributed to the decrease in power. Age contributed to the variability in P(max) independently to the LTVest/quadriceps mass and upsilon(opt). The age-related decrease pattern of P(max) reflects both stabilization (or even increase) of anthropometric measures (LTVest or quadriceps mass) from youth to middleage and systematic decline of upsilon(opt) already from the thirties. This implicates more focus on velocity-orientated training as a means of enhancing leg power and improving functional status.