As the cost of running amounts to about 1 cal per m covered and per kg of body weight, when the aerobic power (VO2, ml/min kg) is known and the energy from glycolysis assumed to be about equal to the energy from oxidations in 1 min, the time employed to cover a given distance can be predicted: a nomogram is given to facilitate the calculation. Conversely from the time employed to cover a given distance the aerobic power in VO2, ml/kg times min can be calculated.