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Aerobic capacity and increase in body core temperature during graded exercise testing

Persons with higher aerobic capacity were shown to have a greater increase in body core temperature than persons with low aerobic capacity during sustained submaximal exercise at similar relative intensities (Mora-Rodriguez et al, 2010). The aim of this study was to determine the relationship between some indicators of aerobic capacity (maximal oxygen uptake (VO2max), maximum speed (Vmax), speed at the ventilatory anaerobic threshold (VT2), as well as heart rate at VT2 (HRVT2)) and the rate of temperature rise (Tr, delta temp/delta t) in different intensity zones during a graded treadmill exercise test. The participants were 32 physically active males (age (mean±SD) 26.5±6.6 years ; height 179.2±5.0 cm ; body mass 76.8±8.1 kg). Graded treadmill exercise test with speed increments of 0.5 km/h each 30 sec was performed, in controlled thermoneutral conditions, until volitional exhaustion. Ventilatory parameters, heart rate and rectal temperature (measured at 8 cm from anal sphincter) were registered throughout the test. The first and the second ventilatory thresholds (VT1 and VT2), delimiting three intensity zones (low, moderate, and high intensity), were determined by the V-slope method. Tr was calculated for each intensity zone (Tr1 below VT1, Tr2 between VT1 and VT2, Tr3 above VT2). Pearson product-moment correlation coefficients were used to determine the relationship between zone specific Trs and indicators of aerobic capacity (VO2max, Vmax, VT2, HRVT2). Tr1 was significantly related to HRVT2 (r=0.48, p<0.01).Tr2 was related to Vmax and VT2 (r=0.40 and 0.45, respectively, p<0.05) and HRVT2 (r=0.61, p<0.01). Tr3 was related to VT2 and HRVT2 (r=0.38 and 0.39, p<0.05). The direction of all correlations was positive, except for correlations between Tr1 and VO2max, Vmax and VT2, which showed a negative trend. Discussion In all three intensity zones Tr was significantly positively related to some of the aerobic capacity indicators. The positive direction of correlations is congruent with previous findings of a greater activity-related Tr in highly fit than in moderately fit persons (Cheung & McLellan, 1998). The trend of negative correlations between Tr1 and indicators of aerobic capacity suggests a possible fitness-related thermoregulatory differentiation across intensity zones. Aerobically fitter subjects show a slower Tr in the low intensity zone, and a higher one at intensities above VT1, as opposed to persons with lower aerobic capacity. Slower Tr1 could result from a higher mechanical efficiency and/or lower heat production in fitter subjects, or a local-core temperature discrepancy, at intensities below VT1. References Mora-Rodriguez et al. (2010). Eur J Appl Physiol ; 109:973-81. Cheung & McLellan (1998). J Appl Physiol ; 84:1731-9.

rectal temperature ; treadmill testing ; running ; maximal oxygen uptake ; anaerobic threshold ; ventilatory threshold

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