Relationship between aerobic power, blood volume, and thermoregulatory responses to exercise-heat stress

Abstract

To clarify the relationship between aerobic power (VO2max), blood volume (BV), and thermoregulatory responses to exercise-heat stress, we analyzed the cross-sectional relationship between the resting BV, plasma volume (PV), erythrocyte volume (EV), VO2max, forearm blood flow (FBF), and sweating responses during exercise in a hot environment (31 degrees C, 50% relative humidity). Twelve college-aged male subjects with a mean maximal oxygen uptake of 48 (range 42-59) mL.kg-1.min-1, a mean PV of 54 (range 42-72) mL.kg-1, a mean EV of 31 (range 23-43) mL.kg-1, and a mean BV of 85 (range 67-115) mL.kg-1 (measured by the Evans Blue dye dilution method) performed three sessions of 20-min cycle exercise at two levels of intensity (40% and 60% VO2max). The BV, PV and EV correlated positively with peak FBF (r = 0.596-0.711, P < 0.05), the increase of FBF in response to a unit rise in esophageal temperature (Tes; peak delta FBF/peak delta Tes) (r = 0.592-0.656, P < 0.05) and with total sweat loss (TSL) (r = 0.599-0.634, P < 0.05) during the exercise. The VO2max correlated with TSL during exercise at 40% VO2max (r = 0.578, P < 0.05), but not with peak FBF and peak delta FBF/peak delta Tes. The VO2max per lean body mass also showed a significant positive correlation with BV (r = 0.769, P < 0.01), PV (r = 0.706, P < 0.05), and with EV (r = 0.841, P < 0.001). The peak delta FBF/peak delta Tes was correlated positively with peak FBF (r = 0.597-0.830, P < 0.05-0.01) and negatively with peak Tes (r = 0.641-0.769, P < 0.05-0.01) during the exercise at the two levels. However, the chest sweat rate (CSR), TSL, and the increase of CSR in response to a unit rise in Tes (peak delta CSR/peak delta Tes) showed no correlation with peak Tes during the exercise at the two levels. These findings suggest that 1) heat dissipation responses during exercise were related more to blood volume than aerobic power and 2) skin blood flow was related more to body temperature than sweating responses during exercise under mild heat stress.

The cross-sectional relationships among hyperthermia-induced hyperventilation, peak oxygen consumption, and the cutaneous vasodilatory response during exercise

“…This suggests that highly physically fit subjects have stronger cutaneous vasodilatory responses than those who are less fit. On the other hand, Yoshida et al (1997) reported that there was no correlation between peak DFBF/peak DT oes (the increase in FBF divided by the increase in T oes during exercise from the pre-exercise level) during exercise at 40 and 60% of _ VO 2max and the extent of _ VO 2max . Our findings do not agree with those of Yoshida et al (1997), however, and the reason for this is twofold.…”

“…On the other hand, Yoshida et al (1997) reported that there was no correlation between peak DFBF/peak DT oes (the increase in FBF divided by the increase in T oes during exercise from the pre-exercise level) during exercise at 40 and 60% of _ VO 2max and the extent of _ VO 2max . Our findings do not agree with those of Yoshida et al (1997), however, and the reason for this is twofold. First, the peak DFBF/peak DT oes calculated by Yoshida et al is not the same as DFBF/DT oes because the peak DFBF/peak DT oes includes the nonlinear portion of the response curve.…”

“…Previous studies have suggested that the sensitivity of cutaneous vasodilation is affected by blood (plasma) volume (Crandall et al 1994;Fortney et al 1984;Yoshida et al 1997). In a cross-sectional study, for example, Yoshida et al (1997) found that there is a significant linear relationship between peak DFBF/peak DT oes during exercise at 60% of _ VO 2max and blood (plasma) volume.…”

Effectiveness of Exercise-Heat Acclimation for Preventing Heat Illness in the Workplace

“…That is, 40% of the hypervolemia induced by exercise training can be attributed to a thermal stimulus; the remaining 60% appears to be due to non-thermal factors related to exercising. Blood volume linearly correlates to maximal oxygen consumption, and increased blood volume contributes to increases in endurance exercise performance [47]. As a result, heat acclimation improves maximal aerobic exercise performance [10,24].…”

Addition of Whey Peptides to a Carbohydrate-electrolyte Drink Enhances its Effect on the Early Treatment of Dehydration in Rats

“…Dehydration also exerts various negative effects on the human body, such as the deterioration of exercise performance (Sawka, 1992;Yoshida et al, 1997), fatigue (Gonzalez-Alonso et al, 1999), and impaired cognitive function (Wilson and Morley, 2003). It is thus important that dehydration is addressed early by rehydration.…”