Can gender differences during exercise-heat stress be assessed by the physiological strain index?

A physiological strain index (PSI) based on rectal temperature (T-re) and h eart rate (HR) was recently suggested to evaluate exercise-heat stress. The purpose of this study was to evaluate PSI for gender differences under var ious combinations of exercise intensity and climate. Two groups of eight me n each were formed according to maximal rate of O-2 consumption ((V) over d otO(2max)). The first group of men (M) was matched to a group of nine women (W) with similar (P > 0.001) (V) over dotO(2max) (46.1 +/- 2.0 and 43.6 +/ - 2.9 ml.kg(-1).min(-1), respectively). The second group of men (MF) was si gnificantly (P < 0.001) more fit than M or W with (V) over dot O-2max of 59 .1 +/- 1.8 ml.kg(-1).min(-1). Subjects completed a matrix of nine experimen tal combinations consisting of three different exercise intensities for 60 min [low, moderate, and high (300, 500, and 650 W, respectively)] each at t hree climates/comfortable, hot wet, and hot dry [20 degrees C 50% relative humidity (RH), 35 degrees C 70% RH, and 40 degrees C 35% RH, respectively]. No significant differences (P > 0.05) were found between matched genders ( M and W) at the same exposure for sweat rate, relative (V) over dotO(2max) (%(V) over dotO(2max)), and PSI. However, MF had significantly (P < 0.05) l ower strain than M and W as reflected by %(V) over dotO(2max) and PSI. In s ummary, PSI applicability was extended for exercise-heat stress and gender. This index continues to show potential for wide acceptance and application .