The maximal explosive power (wmax), i.e. the mechanical power developed over short bursts (less than 5 s) of all-out cycling, or uphill running, in humans attains 12-17 W*kg-1 in non athletics subjects. Thus, in terms of O2 consumption wmax is about four times larger than the subjects VO2max. The peak instantaneous power during a vertical jump off both feet (w) in non athletic subjects is about 50-55 W kg-1 and attains 70-75 W*kg-1 in "power" athletes. Both wmax and w decrease when the all-out efforts is performed from a priming aerobic exercise: if the intensity of this last approaches VO2max, then wmax and w are reduced to about 75% the value attained from rest. Thus, in the course of high intensity efforts, an athlete can develop a still remarkable fraction of his maximal absolute power. The decrease mentioned above is proportional, and presumably causally related, to the decrease of the high energy phosphate concentration occurring in the muscle at the onset of the exercise, and maintained throughout the effort duration.