A Comparison of Nighttime Sleepiness, Performance, and Body Temperature between Morning-Type and Evening-Type Persons

Yoon, J S; Kook, S H; Shin, I S; Shin, M S; Choi, Y; Lee, M S; Lee, H Y

Abstract

OBJECTIVES
The main purpose of this study was to investigate the possible differences in sleepiness, performance, and body temperature during the night between morning(M) and evening (E) type subjects.
METHODS
After a survey study, to verify the validity and reliability of the Korean translation of the Horne and Ostberg's Morningess-Eveningness Questionnaire(1976), 8 extreme M-type subjects (3 males, 5 females) and 8 extreme E-type subjects(3males, 5 females) were selected from the university student population who had participated in the survey study. All subjects underwent sleep latency test and a battery of performance tests at intervals of 2 hours through the night, from 23:00 to 07:00. Oral temperature of each subject was taken every hour from 21:00 to 8:00. Between the testing times, the experimenters ensured that subjects remained awake.
RESULTS
More profound sleepiness was found in the M-type compared to the E-type throughout the night, with significant differences in sleepiness occuring at 23 : 00 and 01 : 00 hours. Overall performance efficiency tended to be lower through the night in the M-type than in the E-type on all tests. A difference in time of temperature minimum between the two types was not noteworthy. Rather, there appeared to be a substantial difference in temperature level during the declining phase, with the temperature of the M-type being lower than that of the E-type.
CONCLUSIONS
These results indicate the existance of a temporal relationship between sleepiness, performance and body temperature during night work. Since the M-type exhibited greater sleepiness and lower performance efficiency overnight than the E-type, it may be assumed that the E-type is more suitable for and tolerable to night work. There was some discussion of the limitations in generalizing these results together with some suggestions for future studies.