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MUSCULAR exercise is accompanied by acceleration of the heart rate. The factors which determine this acceleration, and the heart rate attained in various standard degrees of exercise, have been studied in numerous experiments.After completely denervating the heart of a dog, and excluding chemical stimulation from the adrenal medulla and from the liver, Campos, Cannon, Lundin and Walker [1929] found that the heart rate was only slightly accelerated (12 beats at most), and that the muscular performance on a treadmill was greatly diminished. Samaan [1935], who performed a similar experiment after cutting the cardio-accelerators, except that he suppressed vagal impulses by atropine, noted that the heart rate never rose more than 18-29 beats instead of 110-130. His animals then performed the standard exercise with difficulty and showed intense signs of exhaustion. On the other hand, when the accelerator nerves alone were excluded by removal of the upper thoracic sympathetic chains, the dogs performed the standard work with apparent ease. Indeed Samaan makes the statement that in such animals, deprived of the nerves which positively make the heart beat more rapidly, the maximum capacity for doing work is markedly augmented.In dogs deprived of the cardio-accelerator and splanchnic innervations determinations of the maximal endurance show a definite increase of the capacity comparable with that observed in animals without cardio-accelerator sympathetic innervation according to S a ma a n. However, the maximal tachycardia which was observed towards the end of the standard work was 105-121, an increase Advanced fellow of the C.R.B. Educationa Foundation. 23-2

Measurement procedures and preliminary data are described for continuous cardiac and respiratory function measures with both normal and handicapped individuals. These methods allow (1) extensive sampling of the phenomena, (2) maximum freedom of action by the subject, and (3) minimal stress to the subject due to the measuring instruments.

Total cardiac cost is a measurement of the area under the curve obtained by plotting the heart rate for each minute during work and recovery. In a constant environment it varies with the work accomplished in a given time and, for a constant work performance, it varies with the severity of the conditions. The work accomplished per beat has a reciprocal relation to total cardiac cost when work and recovery times are constant. Recovery cost and the average of three early recovery heart rates, P1, P2, and P3, vary linearly with total cardiac cost when work or environmental stress increases. In these experiments P1, P2, and P3 are the heart rates per minute recorded during the last 30 sec of the 1st, 2nd, and 3rd min, respectively, of the recovery period. These recovery pulse rates provide a simple measurement of the degree of cardiac strain induced by work in any environment. cardiac cost; recovery pulse rates; work rate; warm environment; human male; human female Submitted on July 13, 1961

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