RESUMEN
The aim of the study was to compare the effect of skin surface menthol application on rectal temperature (Tre) during prolonged immersion in cool and cold water. We hypothesized that menthol application would lead to a slower Tre decline due to the reduced heat loss as a consequence of the menthol-induced vasoconstriction and that this effect would be attenuated during cold-water immersion. Six male subjects were immersed for 55 minutes in stirred cool (24°C) or cold (14°C) water immediately after attaining a Tre of 38°C by cycling at 60% of maximum heart rate on two occasions: without (ΝM) and with (M) whole-body skin application of menthol cream. Tre, the proximal-distal skin temperature gradient, and oxygen uptake were continuously measured. ANOVA with repeated measures was employed to detect differences among variables. Significance level was set at 0.05. The area under the curve for Tre was calculated and was greater in 24°C M (-1.81 ± 8.22 a.u) compared to 24°C NM (-27.09 ± 19.09 a.u., P = .03, r = .90), 14°C NM (-18.08 ± 10.85 a.u., P = .03, r = .90), and 14°C M (-11.71 ± 12.58 a.u, P = .05, r = .81). In cool water, oxygen uptake and local vasoconstriction were increased (P ≤ .05) by 39 ± 25% and 56 ± 37%, respectively, with menthol compared to ΝM, while no differences were observed in cold water. Menthol application on the skin before prolonged immersion reduces heat loss resulting in a blunted Tre decline. However, such a response is less obvious at 14°C water immersion, possibly because high-threshold cold-sensitive fibers are already maximally recruited and the majority of cold receptors saturated.
Asunto(s)
Regulación de la Temperatura Corporal , Temperatura Corporal , Frío , Mentol/administración & dosificación , Vasoconstricción , Adulto , Frecuencia Cardíaca , Humanos , Inmersión , Masculino , Consumo de Oxígeno , Piel , Temperatura Cutánea , Agua , Adulto JovenRESUMEN
We hypothesized that menthol application on the skin would enhance vasoconstriction of subjects immersed in cool water, which would reduce heat loss and rectal temperature (Tre) cooling rate. Furthermore, it was hypothesized that this effect would be greater in individuals acclimatized to immersion in 24 °C water, such as swimmers. Seven swimmers (SW) and seven physical education students (CON) cycled at 60% VO2 max until Tre attained 38 °C, and were then immediately immersed in stirred water maintained at 24 °C on two occasions: without (NM) and with (M; 4.6 g per 100 mL of water) whole-body skin application of menthol cream. Heart rate, Tre, proximal-distal skin temperature gradient, oxygen uptake (VO2 ), electromyographic activity (EMG), and thermal sensation were measured. Tre reduction was similar among SW and CON in NM and CON in M (-0.71±0.31 °C in average), while it was smaller for SW in M (-0.37±0.18 °C, P < 0.01). VO2 and heart rate were greater in M compared with NM condition (P = 0.01). SW in M exhibited a shift of the threshold for shivering, as reflected in increased VO2 and EMG activity, toward a higher Tre compared with the other trials. Menthol application on the skin before immersion reduces heat loss, but defends Tre decline more effectively in swimmers than in non-swimmers.