Characteristics of circadian rhythm in six variables of morning active and evening active healthy human subjects.

ABSTRACT

Ten apparently healthy human subjects, inhabitants of dry and hot tropical climate, volunteered for the study. They were instructed to self-measure, several variables, such as oral temperature, heart rate, subjective fatigue, subjective drowsiness, finger counting speed and random number adding speed, daily, preferably at an interval of 4h, for 10-15 days. However, they were instructed to have ad libitum sleep and not to truncate sleep for the sake of self-measurements. The subjects were categorized into two groups, viz, morning active and evening active and their circadian time structure in the above mentioned variables was studied. The results clearly show a higher order of internal synchronization among all the variables. Comparison of acrophase locations between morning active and evening active individuals reveals that the peaks in oral temperature, heart rate and random number adding speed occurs earlier in morning active individuals (P < 0.002, P < 0.005, P < 0.001, respectively). The circadian profiles obtained in this study may serve as guide lines in the study of human health and diseases.