Cardiac Frequency in Relation to Aerobic Capacity for Work

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Abstract
Cardiac frequency (ƒH) and oxygen consumption (V˙o 2) during the transition from rest to exercise in relation to the aerobic capacity for work were studied in an Olympic athlete and a healthy male subject. 1. The behaviour of the ƒH) and V˙o 2 during the early phase of exercise was remarkably similar in both subjects. As exercise was increased in intensity a level of exercise was reached at approximately 1700 cc/min in the non-athlete and 3000 cc/min in the athlete, beyond which the exchange ratio (R) began to show its first marked rise, the O2 debt curve departed from its rectilinear form, ƒH) began to exhibit a slower secondary rise to a delayed steady state value. The underlying mechanisms responsible for, and the implications of these observed changes are discussed, It is suggested that the ƒH) during early exercise might be used to characterise the aerobic capacity of the individual. 2. In order to investigate this problem further an analysis of healthy subjects of different ages and sex was presented. It was shown that the delayed rise in ƒH) only became marked at levels of exercise corresponding to 55–60 per cent of predicted V˙o max 2 in well trained subjects and 45–55 percent predicted V˙o max 2 in less fit individuals. It was thus independent of sex, and age related only to the fitness of the individual. 3. The possible use of an index derived from the adaptation of the heart rate to exercise (PDI65) as a basis for a simple rational test of capacity for aerobic work is discussed.

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