Effects of Waking Time and Breakfast Intake Prior to Evaluation of Physical Performance in the Early Morning

Diurnal variation in both core body temperature and indicators of physical performance are usually observed when measures are taken at 06:00 and 18:00h. However, differences have been reported between findings in the literature; this may be in some part due to methodological reasons, such as if the experimenter allowed subjects to eat breakfast before the morning 06:00h session, or even the waking time of subjects. Eleven diurnally active male subjects participated in four test sessions to examine if the time of morning wakening (04:00 or 05:00h) and eating or not eating breakfast influence body temperature, flexibility, force production, and aerobic performance at 06:00h. All four sessions were separated by 36h and were completed in a counterbalanced order. Each test session comprised a sit-and-reach test, an arm maximal voluntary torque evaluation (isometric, concentric at 1.05 rads-1 and at 4.19 rads-1), and a 10min all-out cycle ergometer test. Our results indicate the effects of waking time or food intake depend on the parameter tested. Consequently, we advise researchers to take care in experimental design and to at least standardize the time of awakening and consumption of breakfast.