PHYSIOLOGICAL-RESPONSES TO COLD STRESS DURING PROLONGED INTERMITTENT LOW-INTENSITY AND HIGH-INTENSITY WALKING

In a previous study [Am. J. Physiol. 272 (Regulatory Integrative Comp. Physiol. 41): R226-R233, 1997], the physiological responses to 240 mi n of intermittent low-intensity walking exercise in a cold (+5 degrees C), wet, and windy environment (Cold) may have been influenced by a 1 20-min preceding phase of intermittent higher-intensity exercise. Furt hermore, the physiological responses observed during this latter phase may have been different if it had been more prolonged. To address the se questions, active men attempted a 360-min intermittent (15 min of r est, 45 min of exercise) exercise protocol in Cold and a thermoneutral . environment (+15 degrees C, Neutral) at a low (0% grade, 5 km/h; Low ; n = 14) and a higher (10% grade, 6 km/h; High; n = 10) intensity. Du ring Low, rectal temperature was lower in Cold than in Neutral, wherea s O-2 consumption, carbohydrate oxidation, plasma norepinephrine and e pinephrine, and blood lactate were higher. During High, Cold had a sim ilar but less marked influence on the thermoregulatory responses to ex ercise than during Low. In conclusion, the physiological responses to Low are similarly influenced by Cold whether or not they are preceded by High. Furthermore, during intermittent exercise up to an intensity of similar to 60% of peak O-2 consumption, a cold, wet, and windy envi ronment will influence the physiological responses to exercise and pot entially impair performance.