Thermoregulatory and perceptual responses of lean and obese fit and unfit girls exercising in the heat

Objective

To verify the thermoregulatory and perceptual responses of obese and lean girls, either fit or unfit, exercising in the heat at a similar rate of metabolic heat production per unit body mass.

Methods

A total of 34 pubescent girls were allocated in four groups: 12 obese fit, 9 obese unfit, 5 lean fit, and 8 lean unfit. The obese groups (13.2 ± 1.4 years, 40.5% ± 5.8% fat by DXA) differed in their aerobic fitness ($\dot{V}{O}_{2peak}$ 76.0 ± 8.1 vs. 56.6 ± 5.8 mL.kg muscle mass^‐1.min⁻¹), as well as the lean groups (13.1 ± 1.6 years, 24.0% ± 4.8% fat) ($\dot{V}{O}_{2peak}$ 74.5 ± 2.9 vs. 56.2 ± 5.0 mL.kg muscle mass⁻¹ min⁻¹). Girls cycled two bouts of 25 min with a 10 min rest in between, at ∼5.4 W.kg⁻¹ in the heat (36 °C and 40% relative humidity) and they were kept euhydrated. Rectal and skin temperatures and heart rate were measured every 5 min. Perceptual responses were evaluated throughout the exercise.

Results

Initial rectal temperature was higher in the obese subjects compared to the lean subjects (37.5 ± 0.3 and 37.2 ± 0.3 °C). No difference was observed among the girls whom were obese (eight fit or unfit) and lean (also fit or unfit) throughout the exercise in rectal temperature (37.6 ± 0.2, 37.5 ± 0.3, 37.5 ± 0.3, 37.4 ± 0.3 °C, respectively), skin temperature (34.8 ± 0.8, 35.1 ± 1.0, 34.4 ± 0.9, 35.2 ± 0.9 °C), and heart rate (128 ± 18; 118 ± 12, 130 ± 16, 119 ± 16 beats min⁻¹). No differences were observed in perceptual responses among groups.

Conclusion

Regardless of the adiposity or aerobic fitness, pubescent girls had similar thermoregulatory and perceptual responses while cycling in the heat at similar metabolic heat production.