The Energy Cost of Sprint Running and the Energy Balance of Current World Records from 100 to 5000 m

Abstract

The time course of metabolic power during 100–400 m top running performances in world class athletes was estimated assuming that accelerated running on flat terrain is biomechanically equivalent to uphill running at constant speed, the slope being dictated by the forward acceleration. Hence, since the energy cost of running uphill is known, energy cost and metabolic power of accelerated running can be obtained, provided that the time course of the speed is determined. Peak metabolic power during the 100 and 200 m current world records (9.58 and 19.19 s) and during a 400 m top performance (44.06 s) amounted to 163, 99 and 75 W kg−1, respectively. Average metabolic power and overall energy expenditure during 100–5000 m current world records in running were also estimated as follows. The energy spent in the acceleration phase, as calculated from mechanical kinetic energy (obtained from average speed) and assuming 25% efficiency for the transformation of metabolic into mechanical energy, was added to the energy spent for constant speed running (air resistance included). In turn, this was estimated as: (3.8 + k′ v2) · d, where 3.8 J kg−1 m−1 is the energy cost of treadmill running, k′ = 0.01 J s2 kg−1 m−3, v is the average speed (m s−1) and d (m) the overall distance. Average metabolic power decreased from 73.8 to 28.1 W kg−1 with increasing distance from 100 to 5000 m. For the three shorter distances (100, 200 and 400 m), this approach yielded results rather close to mean metabolic power values obtained from the more refined analysis described above. For distances between 1000 and 5000 m the overall energy expenditure increases linearly with the corresponding world record time. The slope and intercept of the regression are assumed to yield maximal aerobic power and maximal amount of energy derived from anaerobic stores in current world records holders; they amount to 27 W kg−1 (corresponding to a maximal O2 consumption of 77.5 ml O2 kg−1 min−1 above resting) and 1.6 kJ kg−1 (76.5 ml O2 kg−1). This last value is on the same order of the maximal amount of energy that can be derived from complete utilisation of phosphocreatine in the active muscle mass and from maximal tolerable blood lactate accumulation. The anaerobic energy yield has also been estimated, throughout the overall set of distances (100–5000 m), assuming that, at work onset, the rate of O2 consumption increases with a time constant of 20 s tending to the appropriate metabolic power, but stops increasing once the maximal O2 consumption is attained. Hence the overall energy expenditure can be partitioned into its aerobic and anaerobic components. This last increases from about 0.6 kJ kg−1 for the shortest distance (100 m) to a maximum close to that estimated above (1.6 kJ kg−1) for distances of 1500 m or longer.