The Influence of Topical Capsaicin on Thermoregulatory and Perceptual Outcomes During Exercise Within the Heat

3 experimental visits to the laboratory will be conducted. All visits will take place at the University of Nebraska at Omaha, Exercise Physiology Laboratory. Visit 1 will consist of the physical activity readiness questionnaire (PARQ), adverse reaction to capsaicin, and body composition (hydrostatic weigh, bioelectrical impedance). Visits 2 and 3 will be separated by 7-14 days, randomized, and counterbalanced for experimental (capsaicin) and control (hypoallergenic cream) trials. Both the experimental and control visits will follow the same protocol.

Participants will arrive following an overnight fast state while also refraining from strenuous activity, alcohol consumption, tobacco use, and recreational drugs for the previous 24 hour period. During these visit researchers will apply capsaicin using a gloved hand from shoulder to wrist and mid thigh to ankle (areas outside of the clothing). A hypoallergenic cream will be applied during the control visit.

Exercise will consist of 30 min of moderate intensity treadmill walking (3.5 mph at 5% grade) within a heated temperature/humidity controlled chamber (38°C, 60% relative humidity). Participants will be weighed before, and after completion of the exercise calculate sweat rate. Prior to the exercise session, participants will sit for 5 min in an ambient room temperature environment as a baseline. During baseline and during the exercise core temperature, skin temperature, laser doppler blood flow, galvanic skin response, and heart rate will be collected continuously. Sweat patches will be adhered to the forehead during exercise at minute 10 for collection of sweat composition over the next 10-20 minutes. Thermal perception using the ASHRAE scale (cold to hot) will be assessed pre and during exercise.

EXPERIMENTAL VISIT 1 Visit 1 will take approximately 1 hour. Participants will then complete the physical activity readiness questionnaire (PARQ) to be cleared for physical activity. Participants will have a small amount of the capsaicin cream applied to a small area of the forearm (~2 x 2 in) to test for any adverse reaction over a period of 15 minutes. Those without a reaction will have height, weight, and body fat composition measured. Height and weight will be measured using a medical scale and stadiometer, respectively. Body fat will be assessed with hydrostatic weighing using an electronic load cell based system (Exertech, Dresbach, MN) correcting for residual lung volume or via a bio-electrical impedance analyzer (InBodyUSA, Cerritos, CA).

EXPERIMENTAL VISITS 2 AND 3 Visits 2 and 3 will take approximately 2 hours each. Upon arrival at the lab, a nude body weight will be collected with the subject in a private room. While still in the room, subjects will self-insert a rectal thermistor 12-15 cm beyond the anal sphincter and don a chest strap heart rate monitor. After dressing in their exercise clothing, subjects will exit the private room so that chest, forearm, and calf thermistors can be adhered to the skin with tape. Laser doppler flow (forearm and or/finger) will be adhered with tape and galvanic skin response (fingers) will be adhered using Velcro straps to the skin. Measuring instruments will be recorded using an integrated digital to analog converter (ADInstruments, Colorado Springs, CO).