Purpose. To estimate the energetics and biomechanics of accelerated/decelerated running on flat terrain based on its biomechanical similarity to constant speed running up/down an `equivalent slope` dictated by the forward acceleration (a f). Methods. Time course of a f allows one to estimate: (1) energy cost of sprint running (C sr), from the known energy cost of uphill/downhill running, and (2) instantaneous (specific) mechanical accelerating power (P sp = a f × speed). Results. In medium-level sprinters (MLS), C sr and metabolic power requirement (P met = C sr × speed) at the onset of a 100-m dash attain ~50 J kg-1 m-1, as compared to ~4 for running at constant speed, and ˜90 W kg-1. For Bolt`s current 100-m world record (9.58 s) the corresponding values attain ~105 J/kg m and ~200 W/kg. This approach, as applied by Osgnach et al. (Med Sci Sports Exerc 42:170-178, 2010) to data obtained by video-analysis during soccer games, has been implemented in portable GPS devices (GPEXE©), thus yielding P met throughout the match. Actual O2 consumed, estimated from P met assuming a monoexponential VO2 response (Patent Pending, TV2014A000074), was close to that determined by portable metabolic carts. Peak P sp (W kg-1) was 17.5 and 19.6 for MLS and elite soccer players, and 30 for Bolt. The ratio of horizontal to overall ground reaction force (per kg body mass) was ˜20 % larger, and its angle of application in respect to the horizontal ˜10° smaller, for Bolt, as compared to MLS. Finally, we estimated that, on a 10 % down-sloping track Bolt could cover 100 m in 8.2 s. Conclusions. The above approach can yield useful information on the bioenergetics and biomechanics of accelerated/decelerated running.
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