Human circadian rhythms in heart rate response to a maximal exercise stress

Abstract

Circadian rhythmicity of maximum heart rate response to an exercise task was studied using ten male subjects. Resting heart rate data were collected at seven separate times during a 24 hour period. Exercise heart rate data werecollected at the exact same times, as follows: 0400,0800, 1200, 1500, 1800,2100 and 2400 h. Lowest resting heart rate for all subjects occurred at 0400 h, and the highest at 1800 h. Maximum heart rate response to the imposed exercise task, however, did not exhibit a specific circadian rhythmicity in these subjects, for the seven times of day al which the exercise task was imposed.