The effect of dynamic exercise on resting cold thermoregulatory responses measured during water immersion

Abstract

The purpose of this study was to evaluate the effect of exercise on the subsequent post-exercise thresholds for vasoconstriction and shivering measured during water immersion. On 2 separate days, seven subjects (six males and one female) were immersed in water (37.5 degrees C) that was subsequently cooled at a constant rate of approximately 6.5 degrees C x h(-1) until the thresholds for vasoconstriction and shivering were clearly established. Water temperature was then increased to 37.5 degrees C. Subjects remained immersed for approximately 20 min, after which they exited the water, were towel-dried and sat in room air (22 degrees C) until both esophageal temperature and mean skin temperature (Tsk) returned to near-baseline values. Subjects then either performed 15 min of cycle ergometry (at 65% maximal oxygen consumption) followed by 30 min of recovery (Exercise), or remained seated with no exercise for 45 min (Control). Subjects were then cooled again. The core temperature thresholds for both vasoconstriction and shivering increased significantly by 0.2 degrees C Post-Exercise (P < 0.05). Because the Tsk at the onset of vasoconstriction and shivering was different during Pre- and Post-Exercise Cooling, we compensated mathematically for changes in skin temperatures using the established linear cutaneous contribution of skin to the control of vasoconstriction and shivering (20%). The calculated core temperature threshold (at a designated skin temperature of 32.0 degrees C) for vasoconstriction increased significantly from 37.1 (0.3) degrees C to 37.5 ( 0.3) degrees C post-exercise (P < 0.05). Likewise, the shivering threshold increased from 36.2 (0.3) degrees C to 36.5 (0.3) degrees C post-exercise (P < 0.05). In contrast to the post-exercise increase in cold thermal response thresholds, sequential measurements demonstrated a time-dependent similarity in the Pre- and Post-Control thresholds for vasoconstriction and shivering. These data indicate that exercise has a prolonged effect on the post-exercise thresholds for both cold thermoregulatory responses.

Acute head-down tilt decreases the postexercise resting threshold for forearm cutaneous vasodilation

“…It was noted that 1) at rest, the esophageal Th VD was higher in the head-up position (36.81 Ϯ 0.12°C) compared with the head-down position (36.66 Ϯ 0.16°C) (P Ͻ 0.05); 2) exercise produced an expected increase in the T es Th VD in the head-up tilt position (0.24°C) (P Ͻ 0.05); and 3) the increase in the postexercise T es Th VD was attenuated in the headdown tilt position. The increase in the postexercise resting threshold for cutaneous vasodilation confirms a similar increase of warm (i.e., sweating) (7) and cold (i.e., vasoconstriction and shivering) thermal responses (8,9) measured during upright seating.…”

“…IN RECENT STUDIES, THE EFFECTS of exercise on the postexercise threshold of cold (i.e., vasoconstriction and shivering) (8,9) and warm (i.e., cutaneous vasodilation and sweating) (7) thermoregulatory responses have been evaluated during seated upright resting. These studies have indicated that exercise induces a residual effect on thermal control by increasing (ϳ0.3°C) the postexercise resting threshold for cold and warm thermal responses.…”

Health effects of voluntary exposure to cold water – a continuing subject of debate

“…The vasoconstriction of the peripheral blood vessels sets in at an estimated core temperature of 37.1°C when immersed in cold water and a temperature of 37.5°C when immersed in cold water post-exercise [ 16 ]. It should be noted that these participants were at the high side of normal deep body temperature.…”

Human Physiology in an Aquatic Environment

“…Elevated T s significantly affects the shivering and vasoconstriction thresholds (190). When subjects were immersed in 10 • C water with limbs protected but the torso exposed, HR decreased along with ventilation and skin blood flow during the first initial period of immersion.…”