Selective persistence of circadian rhythms in physiological responses to exercise

Area of Science:

• Exercise Physiology
• Chronobiology
• Human Performance

Background:

• Circadian rhythms influence physiological functions.
• Understanding daily variations in exercise response is crucial for optimizing training and performance.

Purpose of the Study:

• To investigate the influence of circadian time on physiological and metabolic responses during rest, exercise, and recovery.
• To determine if circadian rhythms in heart rate, temperature, and metabolic functions are maintained during physical exertion.

Main Methods:

• 15 male subjects performed cycle ergometer tests at equidistant points throughout the day.
• Tests included submaximal and maximal exercise intensities.
• Measurements included heart rate, rectal temperature, oxygen consumption, ventilation, and blood lactate.

Main Results:

• Significant circadian rhythms were observed at rest for heart rate, rectal temperature, oxygen consumption, and ventilation.
• Circadian rhythms in metabolic measures were absent during exercise and post-exercise.
• Heart rate and rectal temperature rhythms persisted throughout exercise, though heart rate amplitude decreased at maximal exertion.
• Muscular efficiency was independent of the time of day.

Conclusions:

• Circadian rhythms in heart rate and core body temperature are maintained during exercise, but metabolic responses become less time-dependent.
• Time of day does not affect muscular efficiency during exercise.
• These findings highlight the robustness of core physiological rhythms during physical stress.