Thermoregulation during marathon running in cool, moderate, and hot environments

Abstract

A well-trained subject, age 38, ran continously for periods ranging from 60 to 165 min on a motor-driven treadmill at 255.7 m/min while confronted with an airflow equivalent to running speed in cool, moderate, and hot environments. After a period of intensive heat acclimatization, treadmill runs were repeated in the moderate and hot conditions. Measurements were also obtained outdoors in a competitive marathon race. Sweat rate (SR) and mean skin temperature (Ts) were linearly related to Tdb. Acclimatization did not alter VO2max or metabolic rate during the treadmill runs, but heart rat (HR),rectal temperature (Tre), and Ts were lower, SR was higher, and maximal run duration longer in the hot environment, postacclimatization. Maximum runs in the hot environment were terminated by a spiralling increase in Tre to hyperthermic levels, due largely to a marked reduction in cutaneous blood flow, probably reflecting cardiovascular overload from the combined muscular and thermoregulatory blood flow demands, coupled with the effects of progressive dehydration. Utilizing partitional calorimetry and the subject's metabolic heat production, two examples of limiting environmental conditions for his marathon running speed were given.

Decay of heat acclimation during exercise in cold and exposure to cold environment

“…Physiological adaptations take, depending on the parameters, as little as three or as much as 14 days of continuous exposure to heat-stress (Armstrong 2000). Fatigue during prolonged exercise occurs earlier at higher environmental temperatures (Saltin et al 1972) but can be delayed after a process of HA (Adams et al 1975;Nielsen et al 1993). It has been suggested that when a person exercises in the heat, the drive to exercise is diminished by increased core temperature (Bruck and Olschewski 1987;Fink et al 1975;Nielsen et al 1990) and that the reduced body temperature after HA results in a prolonged exercise time to exhaustion.…”

Exercise-Associated Hyponatremia

“…The concentration of sodium in sweat varies widely but is usually 15 to 65 mEq/L, with highly fit athletes generally excreting sweat with sodium concentrations Ͻ40 mEq/L (38,76). The volume of sweat during exercise also varies widely, from approximately 250 ml/h to Ͼ2 L/h, again being less in more fit athletes (77,78). This loss of a substantial amount of hypotonic fluid may seem to protect against the development of hyponatremia.…”

Physiological and metabolic responses of female games and endurance athletes to prolonged, intermittent, high-intensity running at 30° and 16°C ambient temperatures

“…The detrimental eects of high environmental temperatures on the performance of prolonged, submaximal exercise have been well established for men (Adams et al 1975;Galloway and Maughan 1997;Suzuki 1980), but, there is a dearth of information about women. In addition, it has been shown that many sports (among them ®eld hockey, rugby and soccer) require men and women to exercise maximally for short periods, lasting perhaps a few seconds, interspersed with longer spells of rest or lower intensity activity (Williams 1990).…”