Concerning the influence of atmospheric conditions upon the pulse rate and “oxygen debt” after running

Abstract

In a series of papers A. V. Hill and Lupton (1, 2) have recently introduced the term “oxygen debt.” They have shown that human muscle just as frog's muscle is capable of “going into debt” for oxygen, of committing itself to future oxidations required to liquidate lactic acid liberated during activity; that it is possible for a healthy man to perform, for a period, muscular exercise so intense that far more oxygen is required than can be supplied through the circulation during the exercise itself, and thus to establish a heavy “oxygen debt,” which is made good during the period of rest following the exertion. Thus in one case they found an “oxygen debt” of about 13 litres following a short period of violent exercise. That an excess of oxygen was required during rest following exercise has been known for many years. Benedict and Cathcart (3) reviewed the older literature in 1913. We quote some interesting statements from this review. In 1845 Vierordt found that following exercise there was a marked and prolonged effect on the carbon dioxide output. In 1859 Edward Smith, in his discussion of the after-effects of work on respiration, wrote, "It is evident that whilst there is during the whole interval of rest an increase in the respiratory changes over that of rest apart from this exertion, the great excess due to the exertion disappears five minutes after rest.” Speck, in 1892, reported the first accurate measurements of the increased metabolism following muscular work. He always found increased CO 2 production and O 2 consumption long after the cessation of work, and that this increase in metabolism was accompanied by an increase in pulse rate. Benedict and Cathcart also summarise the results obtained in the former’s laboratories. They give figures showing how the metabolism is raised, during sleep after a period of work, above that during sleep after a period of rest. In these observations the work was prolonged for several hours, and they found the metabolism to be 13 per cent, above the normal, 7 or 8 hours after the muscular work had finished. A. V. Hill and Lupton have used shorter periods of more severe exercise in their experiments on man, and have thrown much light on the processes probably concerned in the “oxygen debt.” They have brought into line the results for the recovery oxidative processes in frog’s muscle and those in human muscle. In previous papers it was found that the pulse rate is much greater when working on a bicycle ergometer for 15 minutes (4), or walking on a moving platform for 60 minutes (5) under low cooling powers, that is, warm conditions, than when under cooler conditions. In the present paper, in addition to studying further the pulse rate, we have tested the “oxygen debt” as an indicator of the effects of different atmospheric conditions on man during running on a moving platform. The theory which led to these observations was as follows: the heart has to send much more blood to the skin under hot conditions in order to cool the body; the “oxygen debt” in the muscles may therefore be increased since more lactic acid may be produced in them, as a consequence of less blood, and therefore less oxygen, circulating through them. Fletcher and Hopkins (6) demonstrated that lactic acid was produced in muscle contraction in the absence of oxygen.