Tennis in Severe Heat: Strategies to Avoid Injury.
The relationship between humans and their environment makes a fascinating story. We ordinarily maintain an internal core temperature of about 99 °F, but we live on a planet where surface temperatures vary from -128°F to +136°F.(1) It is important to realize that with simple clothing modifications we can exercise easily at temperatures of less than 0°F, but there is no realistic coping strategy that permits successful vigorous exercise at temperatures above 120°F. Clearly, humans are more adept at managing cold conditions. This notion is echoed by the observation that peak aerobic endurance in untrained athletes occurs at an air temperature of 51°F, and that raising the air temperature to 87°F decreases total aerobic capacity by about 45%.(2)
Exercise in hot conditions triggers a variety of compensatory mechanisms. Two of the most important of these are increased blood flow to the skin and sweating. Sweating is the most powerful heat dissipation mechanism, but sweat must evaporate to have any beneficial effect. The player who is dripping sweat is getting reduced benefit from the fluid his body is losing.
If ongoing exercise in hot conditions produces heat which cannot be dissipated, internal core temperature inevitably rises. It has been shown that most athletes collapse (or cease exercise) when their internal core temperature is in the range of 101°F to 104°F.(3) In fact, those who finish a competition in very hot weather are often those who have allowed their core temperature to rise to excessive levels. As marathon medical director Dr. Joe Wilson said of the Olympics Marathon in Atlanta, "It is the ones who finish who will need our help the most."(4)
The adverse effects of repeated elevations of core temperature to high levels have long been suspected. Many elite marathon runners avoid hard training in high heat because they feel such activity is damaging.(5) It is only recently that epidemiological information has been published on this subject. In a review of hundreds of thousands of Marine Corps recruits training at Parris Island, SC, it was found that exercise-related heat casualties increased progressively as air temperature climbed, beginning at a Heat Index of about 65°F. Unexpectedly, it was demonstrated that the risk of exercise-related heat injuries, even with exercise on relatively mild days, increased significantly if the preceding day had included exercise in very hot weather.(6) A similar pattern was found for exercise-related heat deaths.(7) There is clear evidence that the effects of heat stress are both dose-related and cumulative.
Here are some lessons which tennis players and coaches should take away from these observations:
1. Players should try to maintain top aerobic conditioning year-round. The highly-trained athlete has already attained some degree of heat tolerance.(8)
2. Players should approach abrupt transitions from mild temperatures to hot conditions with caution. A 14-day period of acclimatization is advisable, and initially heat exposure should be at low levels of effort.(9) Even brisk walking for 5 miles daily in hot conditions will provide acclimatization benefits.(17)
3. When fully acclimatized, the player must remember to take in appropriate quantities of fluid before, during and after vigorous exercise. Players should tend to drink on a schedule, remembering that thirst may be a late manifestation of dehydration. There is absolutely no evidence that denying water to athletes makes them tougher, and water restriction clearly promotes the risk of serious heat injury. Remember: As players acclimatize to hot weather, their sweat rates go up and water requirements actually increase. There is no possible adaptation to dehydration. In endurance events, the risk of hyponatremia in athletes who ingest excessive quantities of free water must also be appreciated.
4. The player must realize that even if he is fully acclimatized and in top aerobic condition, he can still sustain serious heat injury. (10) This may be dramatic, such as heatstroke, vomiting or severe cramping. Much more difficult for players and coaches to deal with are the gradual, toxic effects of repeated severe heat exposures. These can result in inability to move quickly, dizziness, poor concentration, and the appearance of lack of motivation. These abnormalities are sometimes mistakenly felt to reflect inadequate dedication, "tennis burn-out" or even mononucleosis, when in fact the culprit is the cumulative effect of repeated low-level heat injuries. The heat-injured player may perform sluggishly for weeks or even months, only to miraculously return to form when cooler weather arrives.
5. To lessen the risk of heat injury, players should limit heat exposure as much as possible. In very hot weather, the warm-up may be shortened. During changeovers, the player should put an iced towel on the neck and drink plenty of water or sports drink. Sitting in the shade lowers air temperature by about 10°F. (11) In extreme conditions, placing the arms in ice water will significantly lower core temperature.(12) In between matches, players should avoid needless heat exposure. They should not sit out in the sun watching matches.(13) Following a difficult match, core temperature can be rapidly lowered by taking a cool bath. In fact, taking a cool bath immediately prior to exercise in severe heat may increase the ability to perform sustained effort.(14)
6. It is the responsibility of coaches and event organizers to schedule training and tournaments in conditions which are most likely to be beneficial. It is in no ones best interest for players to be injured by severe heat exposure. What is little appreciated is that afternoon temperatures in much of the continental US during the summer months routinely climb into the American College of Sports Medicines "High Risk" or "Event Delay" zones.(15) In the summertime, play before 11 a.m. can usually be carried out in reasonable heat stress conditions, and singles matches should be held in this time zone.(16) Doubles matches can be scheduled for afternoon. Keeping players out on the court is by itself a source of heat stress, and in very hot weather no more than two matches per day should be scheduled. Tournaments should be separated on the calendar as much as possible, and whenever possible alternatives to the June 1st to September 15th period of highest heat stress should be provided. Heat stress charts for 239 US cities can be accessed via my web site, http://www.zunis.org.
7. The contract between player and coach is built on trust. The player entrusts himself to the coach, and the coach must put the players well-being above all else. When a player says that he is sick, injured or just not feeling well, the coach must absolutely respect the sincerity of the players word. He must join with the player in finding a good solution to the problem of his illness. This approach "parks the ambulance at the top of the cliff", before serious injury has occurred.
(1) Encyclopedia Britannica.(2)Galloway, SDR and Maughan, RJ: Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man. Med. Sci Sports Exerc. 29: 1240-1249, 1997. (3)Sawka, MN, et al.: Human tolerance to heat strain during exercise: Influence of hydration. J of Appl Physiol 73: 368-75, 1992. (4)Brown, Ben. USA Today, August 9, 1996. (5)Roos, Robert. Heat stress in Atlanta: Preparing for the Olympic worst. The Physician and Sportsmedicine 24: June 1996 (6)Kark, JA, et al. Exertional heat illness in Marine Corps recruit training. Aviat Space Environ Med 67:354-360, 1996. (7)Smith, LE, et al. Unrecognized exertional heat illness as a risk factor for exercise-related sudden cardiac death among young adults. J Am Coll of Card 29 (supl A): 447A, 1997. (8)Aoyagi, Y et al: Interactions of physical training and heat acclimation. The thermophysiology of exercising in a hot climate. Sports Med 23: 173-210, 1997. (9)Ibid. (10)Terrados, N and Maughan, RJ: Exercise in the heat: strategies to minimize the adverse effects on performance. Journal of Sports Sciences 13: Spec No: S55-62, Summer 1995. (11)Martin, DE: Influence of elevated climatic heat stress on athletics. New Studies in Athletics, in press. (12)Jouse, JR, et al.: Prevention of heat strain by immersing the hands and forearms in water. Journal of the Royal Naval Medical Service 83:26-30, 1997. (13)Kurakake, S, et al: A study on the effects of physical load on high school baseball players during midsummer games. Nippon Eiseigaku Zasshi 50: 604-615, 1995. (14)Booth, J, et al: Improved running performance in hot humid conditions following whole body precooling. Med Sci Sports Exerc 29: 943-949, 1997. (15)Coyle, J: Original observation, based on NOAA Environmental Information Summaries C-19, "Heat Stress", Fig. 2, "Average Mid Summer (July) Noon Apparent Temperatures." (16)Coyle, J: Original observation, founded on computer-based summaries of hourly year-long heat stress index values for 239 US cities sampled by the NOAA Solar and Meteorological Surface Observation Network (SAMSON) Database, 1961-1990. (17)Stephens RL and Hoag LL: Heat acclimatization, its decay and reinduction in young caucasian females. Am Ind Hyg Assoc J: 12-17, 1981.
Francis, K, Feinstein, R and Brasher, J: Heat illness in football players in Alabama. Alabama Medicine 60: 10-14, March 1991.
McCann, DJ, Adams, WC: Wet bulb globe temperature index and performance. Medicine and Science in Sports and Exercise 29:955-61, 1997.
Perlmutter, EM: The Pittsburgh Marathon: 'Playing Weather Roulette'. The Physician and Sportsmedicine 14 (8):132-138, 1986.
Nielsen, B: Olympics in Atlanta: a fight against physics. Med Sci Sports Exerc 26 (6): 665-668, 1996
Anonymous: Heat and cold illnesses during distance running. American College of Sports Medicine. Med Sci Sports Exerc 28 (12): I-X, 1996.
Hanson, PG, Zimmerman, SW: Exertional heatstroke in novice runners. JAMA 242:154-157, 1979.
Trapasso LM, Cooper JD: Record performances at the Boston Marathon: biometeorlogical factors. Int J Biometeorol 33: 233-7, 1989.
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