Exercise and the circadian variation in body temperature measures

Area of Science:

• Human Physiology
• Chronobiology
• Exercise Science

Background:

• Circadian rhythms regulate numerous physiological processes, including core body temperature.
• The influence of exercise intensity and duration on circadian temperature rhythms is not fully understood.
• Investigating temporal variations in thermoregulation during physical activity is crucial for understanding exercise physiology.

Purpose of the Study:

• To investigate the presence and characteristics of circadian rhythms in rectal temperature (Tr) and skin temperatures.
• To examine how light (82 W) and medium (147 W) exercise intensities affect these circadian rhythms.
• To determine if exercise duration impacts the observed circadian patterns in thermoregulation.

Main Methods:

• Fifteen male participants underwent measurements of rectal and selected skin temperatures (chest, arm, leg) at six times of day.
• Measurements were taken at rest, during sustained submaximal exercise (5 min), and during graded exercise to exhaustion.
• Post-exercise temperature measurements were also recorded.

Main Results:

• Significant circadian rhythms were observed in rectal temperature (Tr), chest temperature (Tc), and arm temperature (Ta) across all conditions.
• Leg temperature (Tl) rhythms were not significant during maximal exercise and post-exercise.
• Leg temperature showed a significant phase lead compared to rectal and other skin temperatures, particularly at rest and during submaximal exercise.

Conclusions:

• Circadian rhythms are present in core and peripheral body temperatures during rest and exercise.
• Exercise intensity and duration can alter or abolish circadian rhythms in specific skin temperature sites, notably the leg.
• Differential heat conductance between skin sites likely explains the observed phase differences in circadian rhythms.