Journal
JAPANESE HEART JOURNAL
Volume 42, Issue 2, Pages 163-171Publisher
JAPAN HEART JOURNAL, SECOND DEPT OF INTERNAL MED
DOI: 10.1536/jhj.42.163
Keywords
autonomic nervous activity; biological rhythm; exercise
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The purpose of this study was to investigate the diurnal variation and chronotype differences, i.e., in morning-types and evening-types, in post-exercise vagal reactivation. Twelve healthy male college students who were classified as morning-type (6) and evening-type (6), based on responses to a questionnaire, participated in this study. Postexercise vagal reactivation was assessed as the time constant of the beat-by-beat heart rate decrease for the first 30 sec after exercise (T-30) at an intensity lower than the ventilatory threshold. The subjects performed 3-min cycle ergometer exercise at an intensity corresponding to 80 % or the ventilatory threshold after a 1 min warm-up exercise in the morning (7:00 - 8:00) and evening (17:00 - 18 :00) to obtain the T-30. A significant interaction (chronotype-by-time) effect was found for T-30. The morning value of the T-30 in evening-type subjects was significantly larger than their evening value and the morning value in morning-type subjects. There was no significant interaction effect for heart rate and oxygen uptake during exercise. These results suggest that diurnal variation in post-exercise vagal reactivation is different between morning-type and evening-type, and post-exercise vagal reactivation ill evening-type individuals is sluggish in the morning.
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