A comparison of morning and evening "types" during maximum exercise

Twenty-five healthy, untrained, college-age males were determined to be morning, intermediate, or evening chronotypes using the 1976 Horne and Ostberg questionnaire. Each individual underwent a series of three maximal treadmill tests (Bruce protocol) at three different times of day: 1000h-1400h (noon or N test), 0730-0830h (morning or M test), and 1930-2030h (evening or E test). The N test was given one week prior to the M and E tests. The M and E tests were administered a minimum of 48 hours apart using a randomized counter-balanced design. Heart rate, ventilation, oxygen consumption, carbon dioxide production, respiratory exchange ratio, ratings of perceived exertion, and total exercise time were monitored at each test session. Subject grouping, according to the morningness/eveningness questionnaire, revealed a possible age related difference with a higher mean age for the morning types compared to intermediate or evening types. Multivariate analysis of variance did not reveal significant differences in maximum exercise performance according to chronotype or time of day. A trend in maximum exercise heart rate for all subjects was observed with respect to time of day, with lowest values recorded in the morning. While performance differences during maximum exercise were not detected between chronotypes, further study with submaximal exercise intensity and variable duration should be conducted.