Thermoregulatory responses to exercise: relative versus absolute intensity

Area of Science:

• Exercise Physiology
• Human Thermoregulation

Background:

• Understanding deep body temperature regulation during exercise is crucial for athletic performance and safety.
• Previous research by Saltin and Hermansen (1966) explored this relationship primarily during cycling.

Purpose of the Study:

• To re-examine the relationship between deep body temperature and relative exercise intensity specifically during running.
• To compare thermoregulation responses between runners with high and moderate maximal oxygen uptake (VO2max).

Main Methods:

• Twenty male distance runners were divided into high and moderate VO2max groups.
• Participants completed two 60-minute treadmill runs: one at a common absolute speed (10.5 km/h) and another at a relative intensity (65% of VO2max).
• Rectal temperature, skin temperature, heart rate, and sweat loss were measured.

Main Results:

• No significant differences in rectal temperature, skin temperature, or heart rate were observed between groups during the relative intensity run.
• During the common absolute speed run, the moderate VO2max group exhibited significantly higher rectal temperatures (38.19°C vs. 37.70°C) and sweat loss (1.05 kg/h vs. 0.82 kg/h) compared to the high VO2max group.
• Heart rates also differed between groups during the initial 20 minutes of the common speed trial.

Conclusions:

• The findings support the hypothesis that the set-point for maintaining body temperature during exercise is related to relative exercise intensity.
• Individual differences in VO2max may influence thermoregulatory responses, particularly at a fixed absolute exercise intensity.
• This study highlights the importance of considering relative intensity in understanding running thermoregulation.