Submitted on September 29, 2003
Accepted on December 8, 2003
Temperature Regulation during rest and exercise in the cold in pre-menarcheal and menarcheal girls
Panagiota Klentrou1*, Melora Cunliffe1, Jill Slack1, Boguslaw Wilk2, Oded Bar-Or2, Mary Jane De Souza3, and Michael Plyley1
1 Applied Health Sciences, Brock University, St. Catharines, Ontario, Canada
2 Children's Exercise and Nutrition Centre, McMaster University, Hamilton, Ontario, Canada
3 Physical Education and Health, University of Toronto, Toronto, Ontario, Canada
* To whom correspondence should be addressed. E-mail: nota.klentrou{at}brocku.ca.
Thermoregulation during exercise in the cold was examined in 13 adolescent females, aged 13-18y. Six girls with established menstrual cycles comprised the eumenorrheic menarcheal group (EM) and 7 non-menstruating girls comprised the pre-menarcheal group (PM). During the first visit, VO2max, height, weight and % body fat were measured. Second visit included a determination of metabolic rate in thermoneutrality (21°C), consisting of a 10-min rest period and 20-min cycling (30% of VO2max), and a cold test (5°C, 40% humidity, <0.3 m.s-1 air velocity) involving a 20-min rest period and 40-min cycling (30% of VO2max). Subjects in the EM group were tested twice in the chamber, once during the follicular and once during the luteal phase. Heat production-1 in thermoneutrality and in the cold was significantly (p
0.05) higher in the PM compared to the EM girls. However, the PM girls had a significantly (p0.05)lower core temperature in the cold than the EM group. PM also had a significantly higher body surface area-to-mass ratio compared to the EM girls. Although % body fat between groups was not significantly different, within the PM group % body fat explained 79% (p0.01) of the variance in the decrease of core temperature. There were no menstrual phase-related differences in temperature regulation in either the thermoneutral or cold environment. In conclusion, menstrual phase does not influence temperature regulation in females during adolescence. Menarcheal girls had lower metabolic heat production but maintained their core temperature more effectively in the cold than did the pre-menarcheal girls. This thermoregulatory difference between pre-menarcheal and menarcheal girls is mainly a function of geometric differences with maturation-related peripheral vasoconstrictive differences maybe limiting the effectiveness of the mechanism of increased heat storage in younger females.
