Sweat Rate and Hydration Template New Logo...Title: Microsoft Word - Sweat Rate and Hydration...
Transcript of Sweat Rate and Hydration Template New Logo...Title: Microsoft Word - Sweat Rate and Hydration...
The Influence of Hydration on Sweat Rate
Written By: William M. Adams, MS, ATC and Douglas J. Casa, PhD, ATC
Summary of Findings • Scientific Definitions: Hypohydration is the steady-‐state condition of decreased total body
water. Dehydration is the process of losing body water (eg, during exercise). • Sweat rates during exercise vary depending on the exercising individual, environmental
conditions (temperature and relative humidity), fitness level, exercise intensity, duration, equipment worn, and acclimatization status of the individual. During intense exercise in the heat, it is typical to see sweat rates of 1.0-‐2.5 L/h.1–5
• Dehydration causes in a decrease in sweat rate during exercise, which results in a decreased ability for the body to cool through evaporation.
• As environmental temperature and relative humidity rise, the sweat rate of the exercising individual is increased. As sweat rate increases there is an increase in sweat sodium concentration as the body can only reabsorb sodium at a set rate.1
• Heat acclimatization leads to an increased sweat rate during exercise (especially in the heat), smaller reduction in plasma volume, and a lower sweat sodium concentration.1,6,7
• During exercise in the heat most athletes do not replace the fluids that they are losing through sweat. The dehydration that results causes a cascade of events that results in increased cardiovascular strain, increased core temperature as a result of the reduced plasma volume and the impairment of evaporative heat loss due to decreased sweat rate and decreased exercise performance.1,8–12
Change in sweat rate with increasing rectal temperature at varying levels of hypohydration.13
References 1. Sawka MN, Montain SJ. Fluid and electrolyte supplementation for exercise heat stress. Am J Clin Nutr. 2000;72(2 Suppl):564S–72S. 2. Murray B. Hydration and physical performance. J Am Coll Nutr. 2007;26(5 Suppl):542S–548S. 3. Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377–390. doi:10.1249/mss.0b013e31802ca597. 4. Coyle EF. Fluid and fuel intake during exercise. J Sports Sci. 2004;22(1):39–55. doi:10.1080/0264041031000140545. 5. Maughan R. Physiological responses to fluid intake during exercise. In: Maughan R, Murray R, eds. Sports Drinks: Basic Science and Practical Aspects. Boca Raton, FL: CRC Press; 2001:129–52. 6. Maughan R, Shirreffs S. Exercise in the heat: challenges and opportunities. J Sports Sci. 2004;22(10):917–927. doi:10.1080/02640410400005909. 7. Hargreaves M. Physiological limits to exercise performance in the heat. J Sci Med Sport Sports Med Aust. 2008;11(1):66–71. 8. Sawka M, Pandolf K. Effects of body water loss on physiological function and exercise performance. In: Gisolfi C, Lamb D, eds. Perspectives in Exercise Science and Sport Medicine.Vol 3. Caramel: Benchmark Press; 1990:1–38. 9. Sawka MN. Physiological consequences of hypohydration: exercise performance and thermoregulation. Med Sci Sports Exerc. 1992;24(6):657–670. 10. Montain SJ, Latzka WA, Sawka MN. Control of thermoregulatory sweating is altered by hydration level and exercise intensity. J Appl Physiol Bethesda Md 1985. 1995;79(5):1434–1439. 11. Sawka MN, Francesconi RP, Young AJ, Pandolf KB. Influence of hydration level and body fluids on exercise performance in the heat. Jama J Am Med Assoc. 1984;252(9):1165–1169. 12. Casa DJ. Exercise in the Heat. II. Critical Concepts in Rehydration, Exertional Heat Illnesses, and Maximizing Athletic Performance. J Athl Train. 1999;34(3):253–262. 13. Sawka MN, Young AJ, Francesconi RP, Muza SR, Pandolf KB. Thermoregulatory and blood responses during exercise at graded hypohydration levels. J Appl Physiol Bethesda Md 1985. 1985;59(5):1394–1401.
Practical Applications • Athletes should maintain an appropriate level of hydration prior to the start of exercise
in the heat and aim to minimize fluid losses during the event to attenuate any performance decrements.
• Athletes should know their individual sweat rates and fluid needs in order to minimize fluid losses during exercise, especially in the heat.
• As environmental temperature and humidity increase, athletes will need to consume more fluid during exercise as their sweat rates will increase to aid in evaporative heat loss. Heat acclimatization further increases an athletes sweat rate during exercise in the heat so additional fluids will be necessary to prevent dehydration.
• Maintaining an appropriate level of hydration during exercise will assist in maintaining plasma volume levels, which will help enhance cardiovascular and thermoregulatory function during exercise.
Looking Ahead • Further research is needed to examine the magnitude in which sweat rates change during
different environmental conditions and hydration status in exercising athletes. This may assist in determining recommended fluid intake levels during exercise during different environmental conditions.
• Further research is needed looking at the adolescent population in regards to factors affecting sweat rates during exercise and the extent of which those affect exercise performance.