Circadian changes in resting heart rate and body temperature, maximal oxygen consumption and perceived exertion

To investigate the existence, magnitude and interplay of rhythmic 24-hour variations in human functions, maximal O2 uptake (VO2max), resting heart rate (ƒH), body temperature (Tb) and rated perceived exertion (RPE) during exercise were measured twice every 2hours over a full day-night cycle. Thirty-one subjects were randomly administered a treadmill test on 24 separate occasions, 48 hours apart. RPE was observed at heart rates of 130, 150 and 170beats/min. Resting T b, and/H were lower (p< 005) in the morning than afternoon or evening. Measurement of [Vdot]O2 max revealed no significant differences throughout 24 hours. RPE was higher (p< 0-05)at 130, 150 and 170HR at 02.00 and 04.00hours than at 20.00, 22.00 and 24.00 hours. T b and ƒH were apparently in phase.and show a sine wave pattern when expressed on a 24-hour scale. These data demonstrate the significance of the circadian variation for the application of functional tests.