A wide range of physiological factors can be assessed during exercise including heart rate, ventilation, oxygen consumption, lactate levels, core temperature, and skin temperature. Core temperature and heart rate are considered to be the two primary determinants of physiological strain associated with heat stress. Perceptual responses can be assessed from RPE and temperature sensation scales. Both physiological and perceptual factors have been shown to have a solid correlation with one another. The relation between heart rate and RPE is highly correlated and becomes more apparent when heat is added to the equation.