Tip of the Month -- May 2006 

Acclimatization – Key to Maximizing Performance in the Heat

Spring is here and although temperatures are still mild, now is the time to prepare for performing in the heat.  An athlete who is not accustomed to the heat is more susceptible to the dangers of dehydration and heat illnesses.  Prior to strenuous exercise in a hot environment, the most critical measure to take is to expose the athlete to exercise in the heat gradually and on consecutive days. This process, defined as heat acclimatization (HA), stimulates adaptive changes that will improve exercise performance and heat tolerance, reducing both physiological strain and also the athlete’s risk for some forms of heat illness.

These adaptations have been shown to occur at varying stages over the course of approximately 9-10 days:

Heart rate reduction

Plasma volume expansion

Core temperature reduction

Decrease in perceived exertion

Sweat sodium and chloride may decrease (when consuming a low sodium diet)

Renal sodium and chloride concentration reduction

Researchers from the University of Connecticut have developed specific guidelines for acclimatization and hydration while exercising in the heat:

1. Attain adequate fitness in cool environments before attempting to heat acclimatize.

2. Exercise at intensities greater than 50% maximal capacity and gradually increase the duration (up to 90 min/day) and intensity of the exercise sessions during the first two weeks.

3. Perform highest-intensity workouts during the cooler morning hours or evening hours and other training during the hottest time of the day.

4. Monitor core temperature to ensure that body temperature stays within safe limits.

5. Monitor body weight to ensure that proper hydration is maintained as sweat rate increases.

6. Athletes who live in a cool environment but will travel to a hot environment for competition can induce partial acclimatization by wearing insulated clothing, although they should leave some skin surface uncovered and monitor core body temperature to avoid hyperthermia.

These recommendations have been adopted by the National Athletic Trainers’ Association and endorsed by the United States Olympic Committee in preparation for the Barcelona Olympics. Coaches should take every effort to structure training and competitions so that athletes are able to adapt to the environmental stress. In doing so, the environment become less of a threat and performance is maximized.

References

Armstrong, LE. Keeping Your Cool in Barcelona: the Effects of Heat, Humidity, and Dehydration on Athletic Performance, Strength and Endurance. Colorado Springs, CO: United States Olympic Committee; 1992:1-29.

Armstong, LE. Maresh CM. The induction and decay of heat acclimatization in trained athletes. Sports Med. 1991;12: 302-312.