Human Performance Laboratory
Thermal Physiology Laboratory
Since 1990, the study of Human Physiological Responses in Hot Environments has been a distinct research area in the Human Performance Laboratory. Investigations have focused on heat acclimation, the exertional heat illnesses, fluid-electrolyte balance, different modes and timing of rehydration, hyperhydration, highly-trained athletes, and sport supplements/commercial product evaluations.
Our areas of study are described below:
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Highly-Trained Athletes
The majority of studies conducted in our laboratory have utilized highly-trained athletes. We have incorporated UCONN athletes from the Men's and Women's swimming, track & field, basketball, cycling, and volleyball teams.
References:
Hoffman J.R., Maresh C.M., Armstrong L.E., Kraemer W.J. Effects of off-season and in-season resistance training programs on a collegiate male basketball team. Journal of Human Muscle Performance 1(2):48-55, 1991.
Armstrong L.E., Maresh, Whittlesey M., Bergeron M.F., Gabaree C., Hoffman J.R. Longitudinal evaluation of the exercise-heat tolerance and running economy in collegiate distance runners. Journal of Strength and Conditioning Research 8:192-197, 1994.
Maresh C.M., Armstrong L.E., Bergeron M.F., Gabaree C.L., Hoffman J.R., et al. Plasma cortisol and testosterone responses during a collegiate swim season. Journal of Strength and Conditioning Research 8(1):1-4, 1994
Hoffman J.R., Armstrong L.E., Maresh C.M., et al. Strength and Sprint Performance in Wheelchair Athletes. Sports Medicine, Training & Rehabilitation 5:165-171, 1994.
Armstrong L.E. Performing in Extreme Environments. Human Kinetics Publishers, 2000, 334 pages.
Casa, D. J. & C. M. Maresh. Cross-Training: Considerations for the Sports Medicine Physician. Sports Medicine Consult. 1(5):1-6, 2000.
Castellani J.W., Armstrong L.E., Kenefick R.W., Pasqualicchio A.A., Riebe D., Gabaree C.L.V., Maresh C.M. Cortisol and testosterone concentrations in wheelchair athletes during submaximal wheelchair ergometry. European Journal of Applied Physiology 84: 42-47, 2001.
Armstrong L.E., VanHeest J.L. The unknown mechanism of the overtraining syndrome: clues from depression and psychoneuroimmunology. Sports Medicine 32(3):185-209, 2002.
Rosene, J., & Casa, D. J. Hydration in Athletics PASS Course. Champaign, IL, Human Kinetics, To be released Summer 2003. (An online CEU course for ATC's).
Heat Acclimation
Prior to training or competition in a hot environment, heat acclimatization is the primary factor to consider. This process is progressive, requires 10 to 14 days, and may be achieved by exercise in a natural environment (heat acclimatization), in an artificial environment (heat acclimation), or while wearing insulated clothing in a temperate environment (heat acclimation). Caution must be taken with this latter practice, to avoid extreme hyperthermia.
Heat acclimatization involves a unified complex of adaptations that include reduced heart rate, core body temperature, and sodium losses in sweat and urine; in addition, sweat rate increases. These adaptations dramatically reduce the incidence of heat exhaustion and heat syncope because the physiological adaptations include enhanced cardiovascular distribution of blood flow to vital organs. Previous studies in the Human Performance Laboratory have evaluated heat acclimation responses of fit and highly-trained athletes.
References:
Armstrong, L.E. and C.M. Maresh. The induction and decay of heat acclimatisation in trained athletes. Sports Medicine 12:302-312, 1991.
Armstrong, L.E. and C.M. Maresh. Exercise-heat tolerance of children and adolescents. Pediatric Exercise Science 3:239-252, 1995.
Armstrong, L. E.; & Maresh, C. M. Effects of training, environment, and host factors on the sweating response to exercise. International Journal of Sports Medicine 19: S103-S105, 1998.
Armstrong L.E., Stoppani J. Central nervous system control of heat acclimation adaptations: an emerging paradigm. Reviews in the Neurosciences 13(3):271-285, 2002.
Ormerod, J.K., Elliot, T.A., Scheett, T.P., VanHeest, J.L., Armstrong, L.E. and Maresh, C.M. Drinking Behavior and perception of thirst in untrained women during 6 weeks of heat acclimation and outdoor training. Int J Sport Nutr Exerc Metab. 13(1): 15-28, 2003
Armstrong L.E., Stoppani J. Central nervous system control of heat acclimation adaptations: an emerging paradigm. Reviews in the Neurosciences 13(3):271-285, 2002.
Method and Timing of Rehydration
Athletes, athletic trainers and physicians often inquire about the most effective method of replacing fluid losses. They ask, "Is intravenous (IV) fluid replacement superior to oral rehydration?" They also inquire about the timing of fluid replacement. The ask, "Is it best to hydrate long before exercise begins, within a few minutes of the start of exercise, or during exercise?"
Scientific studies have been performed in our laboratory to clarify these matters. These studies observed no performance differences between intravenous and oral rehydration techniques, when the rehydration-rest periods ranged from 20 to 75 minutes between exercise sessions. In terms of exercise performance, there were indications that oral rehydration may be superior, in subtle ways, to intravenous fluid replacement. It is possible, however, that future studies will find some combination of oral and intravenous rehydration that is optimal in this regard.
References:
Castellani, J.W., C.M. Maresh, L.E. Armstrong, R.W. Kenefick, D. Riebe, M.E. Echegaray, D.J. Casa, and V.D. Castracane. Intravenous versus oral rehydration: effects of subsequent exercise in the heat. Journal of Applied Physiology 82:799-806, 1997.
Ekkekakis, P., S. A. Kavouras, D. J. Casa, J. A. Herrera, L. E. Armstrong, C. M. Maresh, & S. J. Petruzzello. Affective responses to a bout of exhaustive exercise in the heat in dehydrated and rehydrated states: In search of physiological correlates. In R. Lidor & M. Bar-Eli (Eds.), Innovations in Sport Psychology: Linking theory and practice. Wingate Institution: Israel, pg 353-356, 1997.
Castellani J.W., Maresh C.M., Armstrong L.E., Kenefick R.W., Riebe D., Echegaray M., Kavouras S., Castracane V.D. Endocrine responses during exercise-heat stress: effects of prior isotonic and hypotonic intravenous rehydration. European Journal of Applied Physiology 77:242-248, 1998.
Casa, D.J., C.M. Maresh, L.E. Armstrong, S.A. Kavouras, J.A. Herrera-Soto, F.T. Hacker, N.R. Keith, and T.A. Elliott. Intravenous versus oral rehydration during a brief period: responses to subsequent exercise in the heat. Medicine and Science in Sports and Exercise 32: 124-133, 2000.
Kenefick RW, Maresh CM, Armstrong LE, Castellani JW, Riebe D, Echegaray ME, Kavorous SA. Plasma vasopressin and aldosterone responses to oral and intravenous saline rehydration. Journal of Applied Physiology 89(6):2117-2122, 2000.
Casa, D. J., C. M. Maresh, L. E. Armstrong, S. A. Kavouras, J. A. Herrera, T. P. Scheett, J. Stoppani, & F. T. Hacker, Jr. Intravenous versus oral rehydration during a brief period: Stress hormone responses to subsequent exercise in the heat. Intern. Journal of Sport Nutrition & Exercise Metabolism. 10:361-374, 2000.
Maresh C. M., J. A. Herrera-Soto, L. E. Armstrong, D. J. Casa, S. A. Kavouras, F. T. Hacker Jr, T. A. Elliott, J. Stoppani, T. P. Scheett. Perceptual responses in the heat after rapid brief intravenous versus oral rehydration. Medicine and Science in Sport and Exercise. 33(6):1039-1045,2001.
Ormerod J.K., Elliott T.A., Scheett T.P., VanHeest J.L., Armstrong L.E., Maresh C.M. Drinking behavior and perception of thirst in untrained women during 6 weeks of heat acclimation and outdoor training. International Journal of Sport Nutrition and Exercise Metabolism 13(1):15-28, 2003.
Fluid-Electrolyte Balance and Dehydration
To maintain exercise performance and to reduce the risk of serious hyperthermia during training sessions, special consideration should be given to the consumption of fluids and electrolytes. Because ad libitum fluid consumption is usually insufficient to meet rehydration needs, numerous studies in the Human Performance Laboratory have evaluated physiological responses and performance changes that occur when profuse, prolonged sweating leads to dehydration.
In contrast, drinking an excessive amount of water can lead to illness or death. For example, mild exertional hyponatremia is defined as a serum sodium concentration between 130-135 mEq¡¤L-1. The prominent signs and symptoms include disorientation, depression, nausea, vomiting, muscular twitching, and grand mal seizure. Severe exertional hyponatremia (serum sodium of less than 125 mEq¡¤L-1) may involve coma, pulmonary or cerebral edema, or respiratory arrest. Only this disorder and exertional heatstroke are potentially fatal to healthy athletes, laborers, and military personnel. Despite these facts, few athletes realize that excessive fluid consumption may cause illness, hospitalization, cognitive impairment, or occupational disability. Reports of exertional hyponatremia most often arise from military training, long hikes, distance running events (3 42.2 km) and triathlons (7 - 17h). Virtually all individuals who experience exertional hyponatremia attempt to drink as much fluid as possible during and/or after exercise. Our publications have focused on the causes, recognition, treatment, and prevention of exertional hyponatremia.
Body weight change, urine color, and urine specific gravity are valid indicators of hydration status. Athletes, coaches and trainers should routinely use these methods to assess pre-exercise hydration status. The widely-used urine color chart was developed in the UConn Human Performance Laboratory.
Both the American College of Sports Medicine and the National Athletic Trainer¡¯s Association have published comprehensive guidelines regarding fluid replacement. Dr. Armstrong and Dr. Casa have been members of the writing groups that prepared Position Statements for these national organizations. During the Spring semester of 2003, graduate students and faculty observed 60 healthy male test subjects for 14 days. Measurements evaluated the effects of consuming three levels of caffeine (0, 200 and 400 mg/day) on fluid-electrolyte balance, psychological factors and thermoregulatory responses, during a 90-minute exercise-heat tolerance test in a 38oC environment.
References:
Armstrong, L.E., C.M. Maresh, J.W. Castellani, M.F. Bergeron, R.W. Kenefick, K.E. LaGasse, and D. Riebe. Urinary indices of hydration status. International Journal of Sport Nutrition & Exercise Metabolism 4:265-279, 1994.
Armstrong, L. E. Hyponatremia in endurance athletes. Sports Medicine Digest (UCLA) 16(9): 1-5, 1994.
Bergeron M.F., Maresh C.M., Armstrong L.E., Signorile J.F., Castellani J.W., Kenefick R.W., LaGasse K.E., Riebe D.A. Fluid-electrolyte balance associated with tennis match play in a hot environment. International Journal of Sport Nutrition & Exercise Metabolism 5:180-193, 1995.
Convertino V.A., Armstrong L.E., Coyle E.F., Mack G.W., Sawka M.N., Senay L.C., Sherman W.M. Exercise and Fluid Replacement. American College of Sports Medicine Position Stand. Medicine and Science in Sports and Exercise 28: i-vii, 1996.
Armstrong, L.E. and C.M. Maresh. 1996. Fluid replacement during exercise and recovery from exercise. In: Body Fluid Balance. Exercise and Sport, edited by E.R. Buskirk, and S.M. Puhl, 259-282. New York: CRC Press. 1996.
Armstrong L.E., Kenefick R.W., Castellani J.W., Riebe D., Kavouras S.A., Kuznicki J.T., Maresh C.M. Bioimpedance spectroscopy technique: intra-, extracellular, and total body water. Medicine and Science in Sports and Exercise 29:1657-1663, 1997.
Armstrong, L.E., J.A. Herrera-Soto, F.T. Hacker, Jr., D.J. Casa, S.A. Kavouras, and C.M. Maresh. Urinary indices during dehydration, exercise, and rehydration. International Journal of Sport Nutrition 8:345-355, 1998.
Casa D.J., Armstrong L.E., Hillman S.K., Montain S.J., Reiff R.V., Rich B.S., Roberts W.O., Stone J.A. National Athletic Trainers' Association Position Statement: fluid replacement for athletes. Journal of Athletic Training 35(2):212-224, 2000.
Armstrong, L.E., Casa D.J. Understanding and identifying dehydration in athletes. Olympic Coach 10(1):8-10, Winter 2000. Distributed to all U.S. Olympic Team Coaches.
Casa, D. J. Rethinking Hydration. The American Journal of Medicine and Sports. 2(4):225-228, 2000.
Casa D.J., Armstrong L.E. Hyponatremia or hype? Letter to the Editor. Physician and Sportsmedicine 29(7):21, 2001.
Echegaray, M., L. E. Armstrong, C. M. Maresh, D. Riebe, R. W. Kenefick, J. Castellani, S. A. Kavouras, & D. J. Casa. Blood glucose responses to carbohydrate feeding prior to exercise in the heat: Effects of hypohydration and rehydration. Intern. Journal of Sport Nutrition and Exercise Metabolism. 11(1):72-83, 2001.
Armstrong L.E. Caffeine: Body Fluid-Electrolyte Balance and Exercise Performance. International Journal of Sport Nutrition & Exercise Metabolism 12(2):189-206, 2002.
Armstrong, L.E. Diuretics. In: Performance Enhancing Substances in Sport and Exercise, edited by MS Bahrke and CE Yesalis. Champaign, IL: Human Kinetics, 2002, pp. 109-116.
Armstrong, L.E. Salt. In: The Encyclopedia of Food and Culture, edited by SH Katz. New York, NY: Charles Scribner's Sons, in press, 2003.
Shirreffs S.M., Armstrong L.E., Cheuvront S.N. Fluid and electrolyte needs for preparation and recovery from training and competition. Journal of Sports Sciences 22(1):57-63, 2004.
Exertional Heat Illnesses
Following the widely-publicized heatstroke death of both a professional football and baseball player, national attention has focused on the exertional heat illnesses among athletes. This attention is warranted because heatstroke, experienced during summer training or competitive events, is a medical emergency.
Other exertional heat illnesses include heat exhaustion, heat cramps, and heat syncope. These illnesses usually occur when competition, peer pressure, or organizational discipline push healthy people beyond the point that they normally would stop exercise, rest, and consume fluids. Physicians, nurses, emergency medical technicians, coaches, athletic trainers, athletes, military leaders, and soldiers can benefit from the dissemination of information regarding the exertional heat illnesses.
Many factors increase a person's risk of heat illness. These factors exist in the following three categories. Inherent host factors include congenital sweat gland dysfunction, cystic fibrosis, hyperthyroidism, inappropriate hormonal responses, and large muscle mass. Acquired factors involve either functional impairment of thermoregulation (e.g., cardiovascular or infectious disease, inadequate nutrient intake, advanced age, obesity, sleep loss, moderate-to-severe dehydration, fluid excess, medications that alter heat dissipation, skin disorders in the miliaria family, lack of heat acclimatization, lack of cardiorespiratory physical fitness) or residual injury (e.g., due to disease, previous heatstroke, deep cutaneous burns). Environmental factors include ambient temperature, humidity, and solar radiation; insulated clothing; enclosed vehicles; and group/peer/competitive pressure to perform exercise beyond one's capacity. Awareness of these factors, and a priori evaluation of each person who plans to exercise or work in a hot environment, is not only prudent but also may spare him/her from serious illness or death.
Both the National Athletic Trainer¡¯s Association and the American College of Sports Medicine have published comprehensive guidelines regarding exertional heat illnesses. Dr. Armstrong and Dr. Casa have been members of the writing groups that prepared Position Statements for these national organizations.
References:
Armstrong, L. E.; DeLuca, J. P., & Hubbard, R. W. Time course of recovery and heat acclimation ability of prior exertional heatstroke patients. Medicine and Science in Sports and Exercise 22: 36-48, 1990.
Armstrong L.E., Maresh C.M. The exertional heat illnesses: a risk of athletic participation. Medicine, Exercise, Nutrition & Health 2:125 - 134, 1993.
Armstrong L.E., Epstein Y., Greenleaf J.E., Haymes E.M., Hubbard R.W., Roberts W.O., Thompson P.D. Heat and cold illnesses during distance running. American College of Sports Medicine Position Stand. Medicine and Science in Sports and Exercise 28(12): i-x, 1996.
Armstrong L.E., Maresh C.M. Can humans avoid and recover from exertional heatstroke? Adaptation Biology and Medicine. Volume 2. Molecular Basis, edited by KB Pandolf, N Takeda, and PK Singal. Narosa Publishing House, New Dehli, India, pp. 344-351, 1999.
Casa, D. J. Prevention of heatstroke: The role of the coach.The Extra Point (The Official Publication of the American Football Coaches Association). September/October 2001, Page 23.
Casa, D. J., A Time to be Bold: Confronting Issues Related to Exertional Heatstroke Before it Occurs. Max! (magazine for New England Chapter of American College of Sports Medicine). Fall 2001, Page 4-5.
Casa, D. J. Don¡¯t forget heat stroke lessons of last summer. Managing School Athletics. 3(11):12, 2002.
Clements, J. M., Casa, D. J., J. C. Knight, J. M. McClung, A. S. Blake, P. M. Meenen, A. M. Gilmer, & K. A. Caldwell. Ice-water immersion and cold-water immersion provide similar cooling rates in runners with exercise-induced hyperthermia. Journal of Athletic Training. 37(2):146-150,2002.
Binkley, H. M., , J. Beckett, D. J. Casa, D. Kleiner, P. Plummer. National Athletic Trainers Association position statement: Exertional heat illnesses. Journal of Athletic Training. 37(3):329-343,2002.
Casa, D. J., & L. E. Armstrong. Exertional heatstroke: A medical emergency. In: Exertional Heat Illnesses, L. E. Armstrong (ed.). Champaign, IL, Human Kinetics Publishers, 2003.
Casa, D. J., & W. O. Roberts. Considerations for the medical staff. In: Exertional Heat Illnesses, L. E. Armstrong (ed.). Champaign, IL, Human Kinetics Publishers, 2003.
Armstrong, L. E., & D. J. Casa. Predisposing factors. In: Exertional Heat Illnesses, L. E. Armstrong (ed.). Champaign, IL, Human Kinetics Publishers, 2003.
Armstrong, L.E. (editor). Exertional Heat Illnesses. Human Kinetics Publishers, in press, April 2003.
Kraemer W.J., Armstrong L.E., Watson G. The effects of exertional heatstroke and exercise-heat acclimation on plasma ?-endorphin concentrations. Aviation Space Environmental Medicine 74:758-762, 2003.
Armstrong, L.E. Impact of severe environments on performance and health. In: U.S. Marine Corps Fitness Correspondence course, edited by S Riewald. Colorado Springs, CO: National Strength and Conditioning Association, 2004, in press.
Hyperhydration
Some athletes have attempted to ¡°store¡± a small excess of fluid in the body, prior to endurance events, as a counter-measure against dehydration and to optimize exercise performance. In some cases, glycerol has been used. This compound is a nontoxic, naturally-occurring product of metabolism that is used as a food additive in some foods. Glycerol enhances fluid retention, above the level achieved with sport drinks or pure water. In 1997, an investigation was conducted in our laboratory to evaluate the effects of glycerol during prolonged, endurance cycling.
Maximizing fluid intake can be dangerous, when carried to extremes. Athletes should attempt to optimize, not maximize, fluid intake without overhydrating. It is useful to know one's rate of sweat production (i.e., body weight lost during exercise) and to match fluid intake during exercise with sweat losses. This can be a challenging proposition but, with practice, athletes can learn to consume ample fluid. Exertional hyponatremia (i.e., low serum sodium concentration of less than 130 mEq¡¤L-1) occurs especially in endurance athletes (see Chapter 6). This medical emergency results from over-consumption of water or other hypotonic fluid. The only certain way to avoid this life-threatening disorder is to consume an ample, but not excessive, volume of fluid.
References:
Armstrong, L.E., W.C. Curtis, R.W. Hubbard, R.P. Francesconi, R. Moore, and E.W. Askew. Symptomatic hyponatremia during prolonged exercise in heat. Medicine and Science in Sports and Exercise 25: 543-549, 1993.
Maresh C.M., Bergeron M.F., Kenefick R.W., Castellani J.W., Hoffman J.R., Armstrong L.E. Effect of overhydration on time-trial swim performance. Journal of Strength & Conditioning Research 15(4):514-518, 2001.
Armstrong, L.E. Thirst. In: The Encyclopedia of Food and Culture, edited by SH Katz. New York, NY: Charles Scribner's Sons, in press, 2003.
Armstrong, L.E. Exertional hyponatremia. Journal of Sports Sciences (UK) 22(1):144-145, 2004.
Temperature Regulation and Uniform Testing
Muscular exercise increases metabolic rate and increases the need to dissipate heat to the environment, to keep inner body temperature from rising to a dangerous level. Environmental heat stress increases the requirement for sweating and circulatory responses. Temperature is regulated by the central nervous system. A small portion of the brain, the hypothalamus, senses the increased body temperature and stimulates (a) sweat glands to secrete sweat and (b) blood vessels to relax, increasing skin blood.
Previous investigations in the Human Performance Laboratory have evaluated the effects of spinal cord injury, cold medications, uniforms, and dehydration on thermoregulation. Studies also have focused on whole-body cooling of exercise-induced hyperthermia.
References:
Armstrong, L.E., Maresh, C.M. Thermoregulation of athletes with spinal cord injury. In: Vista '93--The Outlook, R.D. Steadward, E.R. Nelson, G.D. Wheeler, Eds. Rick Hansen Center, Alberta, Canada, pp 71-81, 1994.
Armstrong L.E., Maresh C.M., Riebe D., Kenefick R.W., Castellani J.W., Senk J.M., Echegaray M., Foley M.F. Local cooling in wheelchair athletes during exercise-heat stress. Medicine & Science in Sports & Exercise 27:211-217, 1995.
Armstrong L.E., Crago A.E., Adams R., Roberts W.O., Maresh C.M. Whole-body cooling of hyperthermic runners: comparison of two field therapies. Am. Journal of Emergency Medicine 14:355-358, 1996.
Armstrong L.E., Maresh C.M., Gabaree C.V., Hoffman J.R., Kavouras S.A., Kenefick R.W., Castellani J.W., Ahlquist L.E. Thermal and circulatory responses during exercise: effects of hypohydration, dehydration, and water intake. Journal of Applied Physiology 82:2028-2035, 1997.
Casa, D. J. Exercise in the heat I: Fundamentals of thermal physiology, performance implications, and dehydration. Journal of Athletic Training, 34(3):246-252, 1999.
Casa, D. J. Exercise in the heat II: Critical concepts in rehydration, exertional heat illnesses, and maximizing athletic performance. Journal of Athletic Training, 34(3):253-262, 1999.
Bolster D.R., Armstrong L.E. Exercise, thermoregulation and precooling. American Journal of Medicine and Sports 2:155-164, 2000.
Armstrong, L.E. Environmental Considerations. ACSM Guidelines for Exercise Testing and Prescription, 7TH edition. Section V, Appendix E. Baltimore, MD: Lippincott, Williams & Wilkins, 2004, in press.
Sport Supplement and Commercial Products
When humans compete, they attempt to take advantage of every legal aid available. In some cases, they use newly-developed or illegal substances to gain an advantage on their opponents. The use of artificial or illegal methods to enhance performance is considered to be inconsistent with the spirit of fair play in sport, and is considered to be unethical. Nevertheless, we all realize that that this spirit of a ¡°level playing field¡± does not exist in reality.
Because the demand for ergogenic supplements [i.e., those that enhance performance] is great, new products are constantly being developed. We recently completed a study that evaluated the effects of creatinine on exercise performance in a hot environment. The manufacturers of sport drinks and other supplements often market their products on the basis of reversing the detrimental effects of dehydration and hyperthermia. Two other studies have evaluated (a) the influence of adding an osmolyte to a sport drink, and (b) the effectiveness of a sport drink that was developed in the Netherlands.
References:
Armstrong, L.E. Considerations for replacement beverages: fluid-electrolyte balance and heat illness. In: Fluid Replacement and Heat Stress. National Academy Press, Washington, D.C., pp. IV-1 to IV-18, 1990.
Maresh C.M., Gabaree C.L., Hoffman, J.R., Hannon D.R., Deschenes, M.R., Armstrong, L.E. et al. Anaerobic power responses to amino acid nutritional supplementation. International Journal of Sport Nutrition & Exercise Metabolism. 1:366-377, 1991.
Miller S.L., Maresh CM, Armstrong LE, Ebbeling CB, Lennon S, Rodriguez NR. Metabolic response to provision of mixed protein-carbohydrate supplementation during endurance exercise. International Journal of Sport Nutrition and Exercise Metabolism. 12(4):384-397, 2002.