Impaired thermoregulation in individuals with a spinal cord lesion can result in elevated cardiovascular and thermal strain during exercise, which may discourage these individuals from participating in regular physical activity, especially that occurring in a warm environment. Physical inactivity increases the risk of developing several morbidities, including coronary heart disease, Type II diabetes, and obesity. Heat acclimation may improve thermal tolerance of spinal cord injured (SCI) individuals, thereby enabling greater comfort during exercise and day-to-day heat stresses, such as outdoor exposures during summer months. The main objective of the proposed project is to test the hypothesis that the degree of thermal impairment in individuals with SCI will be related to the level of the injury and that individuals with SCI can counteract impaired thermoregulation by acclimating to a hot environment. Specific aim 1: Test the hypothesis that in individuals with a spinal cord lesion, the severity of vasomotor and sudomotor function impairments is related to lesion level. Specific aim 2: Test the hypothesis that individuals with SCI can counteract impaired thermoregulation by acclimating to a hot environment, which will 1) improve sweating and skin blood flow, 2) result in lower core body temperature during a given thermal challenge, 3) and result in lower cardiovascular strain (lower heart rate and higher stroke volume) during exercise. Specific aim 1 will be accomplished by conducting a cross-sectional study of differences in thermal and cardiovascular responses between individuals with high and individuals with low spinal cord lesions, as well as able-bodied individuals. Novel techniques will be used to assess expected differences and associated mechanisms. Specific aim 2 will be accomplished by conducting a longitudinal study of the effects and mechanisms of heat acclimation in individuals with SCI.