The Influence of Static Effort on the Respiration and on the Respiratory Exchange

Abstract

(1) The energy cost of static effort.From previous work it appears that the metabolic cost of maintaining a given tension varies directly as the load, provided no new muscles are brought into play as the result of fatigue or local strain. There is conflict of opinion as to the relation of cost to tension; some workers find a linear relation, while others find a non-linear one.In the present observations contractions, which were virtually isometric, were made against a powerful spring, while in a standing position.With constant tension the oxygen cost per contraction varied directly as the duration of the contraction. With constant time and increasing tension the oxygen cost increased more rapidly than the tension.The duration of contraction varied from ½ to 30 sec., and the tension from 30 to 165 Ib. Over the whole range the oxygen cost per contraction is adequately described by the equationQ = T^1·37 (0·0117 + 0·01090t),where Q is the oxygen cost per contraction, T is the tension, and t is the duration of contraction.(2) The effect of static effort on the respiration.As a measure of hyper-ventilation the ratio of ventilation to oxygen intake is used. It is shown that in dynamic work this ratio falls below the resting value, whereas in static effort of whatever severity the ratio increases considerably above the resting value if the effort is sufficiently prolonged. The rise in the ventilation ratio runs parallel with the feelings of strain which are associated with static effort. Pain causes such a rise in the ratio, and the rise which occurs in static effort is ascribed to the influence of painful sensations of strain.Observations were made in which the posture alternated between sitting and standing every 40 sec. The change of posture altered the distribution of the strain, and thus the subjective sensations were not so marked as in the experiments with posture unchanged. In consequence of the postural change the ventilation ratio did not rise sensibly above the resting value, and the maximum strength of pull was increased by 6–16 per cent.