Conditioning In The Heat: Thrive, Not Just Survive

Mindy Millard-Stafford, Ph.D.
Professor of Applied Physiology
Georgia Institute of Technology

As summer/fall pre-season "camp" approaches, coaches and athletic trainers should keep safety foremost in mind and take the necessary steps to maximize the athlete's ability to train optimally during this crucial time of the season. Parents and athletes have an equally important task in understanding the role the hot, humid weather plays in summer workouts.

Even with modest humidity (50 precent), it has been well shown scientifically that protective football equipment (helmet, pads, etc.) greatly hinders the body from dissipating heat. This is true for relatively mild temperatures (76 degrees F) as well as hot (90 degrees F). The consequences can be deadly. In fact, one death in football occurred at 64 degrees F, 100 percent humidity.

The logical alternatives for a sport such as football are: cancel/ reschedule practices or remove the equipment. During the summer months in the Atlantic Coast Conference area, the weather conditions are such that it is practically impossible to find times where the humidity is within "tolerable" limits. While the protective equipment makes football a unique sport for heat injury, all athletes who participate in Fall sports (e.g. soccer, cross country) can be at risk if they are not acclimatized to humid heat and are not already aerobically fit when they report in August. Consequently, what are some practical options for coaches and athletic trainers? What should parents and athletes know?

Exercise intensity is a key determinant in heat injury in addition to the environment. During the first 5-7 days of pre-season conditioning and acclimation, the overall exercise intensity should be reduced. This can be accomplished with more frequent rest periods (and water breaks) and eliminating "all-out" efforts (e.g. suicide wind sprints and prolonged conditioning sets of high intensity) during the first few days of summer conditioning. Allowing more "teaching" time (preferably in cool, shaded areas) interspersed with conditioning drills will aid in keeping core temperatures from spiraling upward during practice.

The most "intense" conditioning should be moved indoors in the air-conditioning or scheduled for early morning before radiant heat (direct sun) peaks. The early emphasis for work-outs in the heat should be building an aerobic base and acclimatization. Gradually build the intensity back into the outdoor practice sessions as acclimatization improves (at least 7 to 10 days). Pre-cooling athletes has also been observed to keep core temperatures lower during subsequent exercise. Therefore, removing protective equipment during rest periods in football and use of ice packs at the neck, arm pits is suggested.

Recovery between practice sessions in air-conditioning is also essential. Although the large, overweight athlete may tend to "overheat" in practice, a recent study which monitored collegiate football players during the 1st week of 2003 summer practice found that the most active players (wide receivers, quarterbacks who scramble) also had some of the highest core temperatures.

Injury surveillance data from the NCAA indicates that injuries (all types) in Fall sports are highest in pre-season practices compared to any other time of the season. Successful pre-season conditioning also can be facilitating by athletes paying more attention to their hydration and recovery practices between work-outs.

Before practice:

Start practice well hydrated. Check body weight at the same time each day (either nude or standard dry clothing) under similar conditions (before eating, after voiding). Day-to-day body weight should be within 1 percent over the first week of practice. This is not a time to stress weight reduction in athletes (as this favors dehydration practices to aid weight loss and puts athletes at greater risk for heat injury).

Check urine color in a cup (not the toilet bowl). Pale yellow color is ideal; gold, orange and brown indicate dehydration (from moderate to severe, respectively). A recent study in our laboratory indicated that prior to a simulated practice in the heat, football athletes have concentrated urine indicative of dehydration, despite instructions to "hydrate well". Providing more specific instructions (drink a certain # bottles before bed or after arising) may enhance compliance.

During practice:

Drink regularly (every 15-20 min) to offset sweat losses. "Know thy sweat rate". Each athlete is very different in terms of sweat rates. In addition, sweat rates can change for each individual as sweat losses will be greater after the athlete becomes heat-acclimatized. Athletes should estimate sweat rates from the difference between pre-practice and post-practice weight loss daily during the pre-season.

Drink water or sports drinks. If practice is < 1 hr, water is adequate for hydration. If longer, sports drinks may enhance performance during practice without delaying gastric emptying and fluid absorption.

Use a buddy system. Athletes should monitor their partner's drinking (give each other reminders) and note their mood or other physical signs of heat injury.

After practice:

Weigh out in the same manner as weighing in. The difference in body weight is almost entirely fluid loss. To regain that fluid and be well hydrated for the next practice, one should drink one to two pints (16-32 ounces) of fluid per pound of weight loss before the next practice. This fluid is in addition to the normal amount of fluid consumed.

Within minutes of the end of practice, ingest a carbohydrate or carbohydrate + protein beverage. Recovery is enhanced when at least 1 g per kg of body weight of carbohydrate or carbohydrate + protein is consumed each hour after practice. For example, a 200 lb. (91 kg) athlete should ingest 91 g (364 calories) of carbohydrate soon after practice. This can be achieved with 1-1.5 liters of a sports drink or a lesser amount in combination with carbohydrate gel, bar, or solid food.

Added salt aids fluid retention. Chicken soup rehydrates better than a sports drink. Sodium losses from sweat are greatest during the early acclimatization process and therefore emphasis on salty foods (pickles, chips, canned soups) can ensure the most complete rehydration during the first week of summer practices. Food replaces some of the fluid loss.

Consider the recovery time between practices as preparation for the next practice. Emphasize to the athlete the importance of adequate rest during the day. Proper recovery reduces the chance for injury.

Another point is to report to the sports medicine staff the use of any over the counter medications or supplements. Medications can alter the body's ability to deal with the heat. If there are any questions, talk to your physician. Athlete education on these points can help them get the most benefit from conditioning in the heat.