Burk, A., Timpmann, S., Kreegipuu, K., Tamm, M., Unt, E., & Ööpik, V. (2012). Effects of heat acclimation on endurance capacity and prolactin response to exercise in the heat. European Journal of Applied Physiology, 112. Online publication, April 10, 2012.

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This study examined the effect of heat acclimation on endurance capacity and blood prolactin response to moderate intensity exercise in the heat in young male subjects (N = 21). Three exercise tests were completed on a treadmill: H1 (walk at 60% VO2peak until exhaustion at 42°C), N (walk at 22°C; duration equal to H1), and H2 (walk until exhaustion at 42°C after a 10-day heat acclimation program). Heart rate, skin and core temperatures and body heat storage (HS) were measured. Blood samples were taken immediately before, during, and immediately after each exercise test.

Heat acclimation resulted in lower heart rate, skin and core temperatures, and body heat storage rate during the exercise tests, whereas endurance capacity increased from ~88.6 minutes in H1 to ~162.0 minutes in H2. Blood prolactin concentration was lower during exercise in H2 compared to H1 but the peak blood prolactin level observed at the time of exhaustion did not differ between the two trials. Blood prolactin concentration at 60 minutes of exercise in H1 correlated with time to exhaustion in H1 and H2.

Implication. Heat acclimation slows the increase in blood prolactin concentration but does not reduce the peak blood prolactin level occurring at the end of exhausting endurance exercise in the heat. Blood prolactin response to exercise in the heat in non-heat-acclimated Ss is associated with their endurance capacity in the heat in a heat-acclimated state.

[The pituitary glands of males and nonpregnant females make prolactin but it is not clear what role it plays. Prolactin levels vary throughout the day with the highest levels occurring during sleep and shortly after waking. Prolactin levels increase during times of physical and/or emotional stress.]

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