Muscular exercise, lactic acid and the supply and utilisation of oxygen.— Parts VII–VIII

Abstract

(A) The relation between oxygen intake and severity of exertion . — When muscular exercise commences, the ventilation of the lungs, the oxygen intake and the carbon dioxide output rise rapidly, in a period of about 2½ minutes, to values characteristic of the severity of the exercise; at these values they remain approximately constant. If the exercise be moderate, i. e ., if the oxygen intake does not approach the maximum for the subject investigated, then the exercise may be continued for a long time: the body is able, so to speak, to provide the energy required “out of income.” If, however, the effort be excessive, the condition of exercise is not stable, the ventilation, the oxygen intake and the carbon dioxide output tend to attain their maximum values, and fatigue and exhaustion gradually or rapidly set in. The relation between these quantities and the magnitude of the effort made is clearly shown in Table I, especially in the series of 14 experiments made on A. V. H. running; at speeds from 2·86 to 4·7 metres per second. These results are plotted as double circles in fig. 1; the other points shown are the results obtained with S., W., and J. (who have approximately the same body-weight and build as A. V. H.), and with C. N. H. L. and H. L. (who are lighter). The observations on the two latter have been “reduced” to the same body-weight as A. V. H. before plotting. The running was on an open-air grass track, about 90 metres round, the speed being kept constant by an observer calling the times of successive laps. In every case the collection of expired gases was preceded by a sufficient foreperiod of exercise (2½ minutes or more) to ensure that a steady condition was reached. The following conclusions may be drawn from these observations:— (1) At low speeds the ventilation is small and the respiratory quotient is low: the oxygen supply is adequate to the needs of the body, lactic acid does not accumulate, and a steady state is soon attained.