Influence on human sleep patterns of lowering and delaying the minimum core body temperature by slow changes in the thermal environment.

Study Objectives: We hypothesized that appropriate changes in thermal environment would enhance the quality of sleep.

Design/setting: Controlled laboratory study.

Participants: Healthy young men (n = 7, mean age 26 years).

Rectal temperature, distal sweat rate, and forearm blood flow following mild exercise at two phases of the circadian cycle.

Changes in rectal temperature during mild exercise in the middle of the rising (11:00 h) and falling (23:00 h) phases of the circadian rhythm of resting core temperature have been compared. Seven healthy males were studied at rest, while exercising on a cycle ergometer (60 min at 80 W), and during the first 30 min of recovery. Rectal temperature, forearm blood flow, and forearm sweat rate were measured at 1 min intervals throughout.

The circadian rhythm of core temperature: origin and some implications for exercise performance.

This review first examines reliable and convenient ways of measuring core temperature for studying the circadian rhythm, concluding that measurements of rectal and gut temperature fulfil these requirements, but that insulated axilla temperature does not. The origin of the circadian rhythm of core temperature is mainly due to circadian changes in the rate of loss of heat through the extremities, mediated by vasodilatation of the cutaneous vasculature. Difficulties arise when the rhythm of core temperature is used as a marker of the body clock, since it is also affected by the sleep-wake cycle.