INTRODUCTION: Basal heart rate (HRbasal) is measured minutes upon waking up, since it has rhythmic changes throughout the day. OBJECTIVE: Considering the difficulty in achieving the standard conditions for its measurement, the objective was to propose an equation for predicting HR Basal. Therefore, at first, it was necessary to describe the pattern of rhythmicity of HR and study the influence of habitual physical activity level (PAL) on this rhythmicity. METHOD: 90 subjects (54 men and 36 women) filled out the Baecke Questionnaire, median was used to form the PAL A and PAL B groups. The subjects self-assessed HRres at 6, 9, 12, 15, 18, 21 and 24 h using a cardio frequency meter. To describe the rhythmicity and identify the PAL influence, ANOVA followed by Tukey test (p> 0.05) were applied for absolute and normalized values of HRres. The normalized values were adjusted by second-order polynomial to construct the prediction equation, whose validity was tested by Pearson correlation (p> 0.05) and standard error of estimate (SEE). RESULTS: HRres in bpm, of the PAL A group was lower than in the PAL B group at all moments tested: 60 ± 7.5, 64 ± 9.3, 63 ± 8.1, 66 ± 8.7, 66 ± 7,7, 64 and 60 ± 8.1 ± 8.2 compared to: 66 ± 9.6, 11.4 ± 71, 72 ± 11.6, 73 ± 10.8, 10.7 ± 74, 69 ± 9.4 and 10.7 ± 68. Concerning normalized values, no significant differences were found between the two groups and both showed rhythmicity similar to a parabola. The prediction equation showed r 0.70 to 0.83 and SEE from 4.8 to 6.2 bpm. CONCLUSION: HRres presents lower values in more active individuals, but with the same pattern of rhythmicity. This equation enables prediction of FCbasal from the measurement of HRres taken at different times of day.
circadian rhythm; heart rate; physical activity
