Thermoregulatory responses to exercise: relative versus absolute intensity

The purpose of the present study was to re-examine the relationship between deep body temperature and relative exercise intensity, during running rather than cycling (Saltin and Hermansen, 1966). Twenty male competitive and recreational distance runners, aged 22 +/- 0.9 years (mean +/- s((x) over bar)), were selected to form two groups, one with high maximal oxygen uptake (VO2max) values (72.8 +/- 0.8 ml (.) kg(-1) (.) min(-1)) and the other with moderate values (59.4 +/- 0.7 ml (.) kg(-1) (.) min(-1)). The participants completed two 60 min constant-paced treadmill runs at a common speed (absolute intensity) of 10.5 km (.) h(-1) and at a relative exercise intensity at a speed equivalent to 65% Of VO2max. During the relative exercise intensity trial, no differences were found in rectal temperature, skin temperature or heart rate between groups. However, when running at the common speed, differences were identified in rectal temperature. At 60 min, rectal temperature was 37.70 +/- 0.19degreesC and 38.19 +/- 0.11degreesC for the high and moderate VO2max groups, respectively (P < 0.05). Sweat lost was significantly higher in the moderate VO2max group (moderate: 1.05 +/- 0.06 kg (.) h(-1); high: 0.82 +/- 0.08 kg (.) h(-1); P < 0.05). Heart rates were also different between groups over the first 20 min during the common speed trial (P < 0.05). The results of the present study support the findings of Saltin and Hermansen (1966), in that the set-point at which temperature is maintained is related to the relative exercise intensity.