Recovery from exercise at varying work loads: Time course of responses of heart rate and systolic intervals

Abstract

The time course of the recovery period was characterised by non-invasive measurements after 4-minute bicycle exercise at 3 separate (50W, 100W, and 150W) work loads in 10 volunteers in whom the peak responses during exercise of heart rate and systolic time intervals were consistent with previous investigations of comparable subjects. Most responses started immediately to return toward resting control values. Despite rapidly falling post-exercise heart rates, left ventricular ejection times fell further from their exercise nadirs for the first 5 to 15 seconds of recovery (depending on load) probably because of diminished stroke volume caused by venous pooling and, probably also, by continued rapid ejection rate. The stroke volume change was indicated by a concomitant precipitous fall in ejection time index, which then stabilised in tandem with the subsequently normal (i.e. discordant) left ventricular ejection time-heart rate relation. For the first 30 seconds, heart ratefellfrom load-related exercise peaks, but at equal slopes of change for all loads; thereafter, rates of return toward resting control were strictly load-related. Changes in pre-ejection period were determined by changes in isovolumic contraction time; the degree of return toward control of pre-ejection period and isovolumic contraction time from their exercise nadirs was load-dependent throughout recovery; loaddependent differences in their rate of return were pronounced in the first 30 seconds. The rates of change in the ejection time index and in the ratio pre-ejection period/left ventricular ejection time (PEP/LVET) were virtually independent of load throughout most of recovery.