Mechanical and metabolic power in accelerated running-PART I: the 100-m dash

Purpose: Acceleration phases require additional mechanical and metabolic power, over and above that for running at constant velocity. The present study is devoted to a paradigmatic example: the 100-m dash, in which case the forward acceleration is very high initially and decreases progressively to become negligible during the central and final phases. Methods: The mechanical ([Formula: see text]) and metabolic ([Formula: see text]) power were analysed for both Bolt's extant world record and for medium level sprinters. Results: In the case of Bolt, [Formula: see text] and [Formula: see text] attain peaks of ≈ 35 and ≈ 140 W kg-1 after ≈ 1 s, when the velocity is ≈ 5.5 m s-1; they decrease substantially thereafter, to attain constant values equal to those required for running at constant speed (≈ 18 and ≈ 65 W kg-1) after ≈ 6 s, when the velocity has reached its maximum (≈ 12 m s-1) and the acceleration is nil. At variance with [Formula: see text], the power required to move the limbs in respect to the centre of mass (internal power, [Formula: see text]) increases gradually to reach, after ≈ 6 s a constant value of ≈ 33 W kg-1. As a consequence, [Formula: see text] ([Formula: see text]) increases throughout the run to a constant value of ≈ 50 W kg-1. In the case of the medium level sprinters, the general patterns of speed, mechanical and metabolic power, neglecting the corresponding absolute values, follow an essentially equal trend. Conclusion: Hence, whereas in the last part of the run the velocity is about twice that observed after ≈ 1 s, [Formula: see text] and [Formula: see text] are reduced to 45-50% of the peak values.