Exercising in the Heat -- Kenneth Cooper, MD -- 7/30/03

By Kenneth Cooper
WebMD Live Events Transcript

The extreme heat of mid-summer can make it tough to stay motivated to exercise. It can also be downright dangerous without the proper precautions. We discussed staying safe in the heat with the father of aerobics, exercise guru Kenneth Cooper, MD.

The opinions expressed herein are the guest's alone and have not been reviewed by a WebMD physician. If you have questions about your health, you should consult your personal physician. This event is meant for informational purposes only.

Moderator: Welcome back to WebMD Live, Dr. Cooper. How's the weather where you are? Hot?

Cooper: The weather is hot, humid, and today expected to be about 100 degrees with humidity at 50%. The humidity is an important point, because anytime you have temperature and humidity together, and the number exceeds 150, the risk of heat stress is very high. Only people who are acclimatized should be allowed to exercise out of doors with that kind of heat, and I would advise them against vigorous activity. So, short and slow type of activities, if any, ought to be conducted at this time of heat stress. It is the only thing I'd recommend.

Moderator: You mentioned high humidity adding to the potential danger of exercising in extreme heat. What about very dry conditions, such us in the Southwest?

Cooper: If you have a temperature of 100 degrees and humidity of 30% or less, that doesn't carry with it the same risk of heat stress as having a lower temperature, say 90 degrees, with humidity of 60%. So the humidity is extremely important. We have a lot of unexpected heat problems in situations where the temperature is not that high, but humidity is approaching 90%-100%.

Moderator: Tell us about different age groups and how they acclimate differently to the heat.

Cooper: Two age groups the most susceptible to heat are the young and the old. One of the problems is that older people just can't handle the heat stress like they could during their youth. The reason kids absorb more heat from their environment is because they have a larger surface area, the body mass ratio, than adults. The smaller the child, the faster the heat is absorbed. Elderly adults are at danger because there are subtle age-related differences in body fluid balance. Elderly adults must practice a more gradual acclimatization to heat, emphasizing hydration. The reason for that is that elderly adults are more likely, normally, to be dehydrated. If you add dehydration to excessive heat in an elderly adult you are dramatically increasing the risk for heat stress.

Other groups who are very likely to suffer heat stress include the people who spend much of their day in the heat, such as landscapers, construction road crews, and traffic police. With little chance for either fluid consumption or bathroom breaks they tend to drink less fluid throughout the day because bathrooms are not accessible. So it's very important for people in that situation to consume adequate fluids, and make the bathroom breaks whenever necessary.

Finally, athletes and exercisers who spend a lot of time training and competing in the hot daylight hours typically do not drink enough to match fluid loss. Why? Exercise and activity increases the core body temperatures to a point that your body's air conditioning or sweat turns on. As sweat evaporates from your skin, it cools the body. Also as blood circulates between the skin and hot muscle it helps transfer heat out of the body, keeping your body's core temperature in the safe zone. When exercising in the heat, your core body temperature rises more rapidly, because the warmer air makes it harder to dissipate heat from the body.

Your body adapts to warmer weather, as acclimatization, by learning to sweat sooner, and to sweat more, to help keep the body from reaching dangerous heat levels. By sweating sooner and faster, you lose more fluids than before. This means that dehydration is more likely when you're acclimatized to heat. Seems strange, but true. Dehydration can dramatically impair your performance and increase the risk of heat illnesses. Heat illnesses, such as heat exhaustion and heat stroke, are major health hazards and in extreme cases can be deadly to the extent that on the average we lose about 300 people to heat illnesses each year.

Member question: My grandfather is always cold, due to poor circulation. He's nearing 90. Walking in the sun helps him get comfortable. As long as he's not doing anything very strenuous, only walking a mile at most, is he under any extra risk for heat stress? Oh, and he never drinks anything but coffee!

Cooper: Two problems. One, coffee is a diuretic, and makes you lose fluid. You can't consume enough coffee to compensate for the fluid you lose when sweating in a high-temperature environment. Two, anyone 90 years of age, as a rule, is going to be dehydrated, because older people are notorious for not consuming the six to eight glasses of water per day that is recommended for everybody. That's one reason they're very fragile and susceptible, particularly to heat illnesses.

Even though the grandfather is cold, I'd advise against even walking a mile in a very elevated heat situation, for example, above 90 degrees. I advise against that particularly if humidity is above 40%-50%. He will do just as well walking in an air-conditioned environment, mall, or treadmill; that type of exercise invariably will warm the body. I think what he's doing is potentially dangerous, and I would advise against it.

Member question: Dr. Cooper, I seem to itch when I'm outside exercising, usually when I overheat. I'm on Singulair and 20 mg of Zyrtec. Nothing has worked for me and I don't want to go on corticosteroids. Do you know any alternatives? I tried all sorts of antihistamines and creams.

Cooper: That is a common problem. I'm convinced that some people are allergic to their own sweat. It is the salt, potassium, or some other ingredient of sweat causing the response. We don't know. If you are a man, you might find that exercising without a shirt may not cause the same effect as exercising with a shirt on, because that keeps the perspiration and the salt in direct contact with the skin. Of course, that's not practical or possible for a woman. Apparently, that is one of the reasons that some people get an itching response with exercise and sweat.

To the contrary, I've seen a lot of people who are allergic to the cold. They can go from a warm environment to just a moderately cold environment and get hives and itching, almost uncontrollably.

With these patients, either having reaction from heat or from cold, I've never found an antihistamine, such as the ones mentioned, that would work, and usually have to resort to some type of a steroid like prednisone, but that's really dramatic treatment. I would not recommend that. For your situation, try to exercise in a cooler environment, in an air-conditioned area, where the sweat production can be reduced. Hopefully, that will control the itching.

Member question: Doctors, don't think it is a sweat thing. Exercising is not possible without a shirt because I play on sports teams. It is impossible to play in a cooler environment. Do you have any suggestions for possible treatments?

Cooper: No, I wish I did. You should consult with an allergist. I've had this problem with my patients, but I've not seen a remedy for it.

Remember, though, you do not have to exercise and produce sweat to get health and longevity benefits. Our studies clearly show if you walk two miles in 30 minutes, three times a week it reduces deaths, heart attacks, strokes, diabetes, and cancer by 58%, and has the potential of adding six years onto your life. You might say that's fast, walking a four mile-per-hour pace, a 15-minute mile. That's double time in the military. That might produce sweat. Then walk two miles in 40 minutes. That's three miles per hour. That's a 20-minute mile. That's a standard walking speed. But you have to do it five days a week to get the same benefit of reducing deaths from all causes by 58% and increasing life span by six years.

So just avoiding inactivity is the first step of a health and wellness program. We have an estimated 49 million adults who are couch potatoes, totally sedentary, who are shortening their lives by at least six years and increasing death causes by 58%. The most important message I give my exercising patients is listen to your body. If you have an adverse response, if you can't play competitive sports without sweating, try swimming. Try something else. If you have chronic knee, ankle, hip problems with exercise, stop jogging and start walking. Use an elliptical trainer. Where there's the will, there is the way to exercise.

But remember, the older you are, the longer it takes you to get into shape, and the faster you lose it. And fitness is a journey, not a destination. You must continue it for the rest of you life, because there's not way to store fitness. It's what you did yesterday that counts, not what you did six weeks ago.

Member question: I'd like to swim laps since it is so hot. How many do I have to do to have an effect? Does it matter what stroke I use? Is one better than another? Should I vary the stroke?

Cooper: We have two swimming pools at the Cooper Aerobic Center in Dallas. We've found that in the hot weather swimming is an excellent alternative. We've found, too, though, that we have to aerate the water, to keep it cool. Otherwise, it's very difficult for the people to swim and not have some heat stress problems. You wouldn't believe that you can sweat while swimming, but you can. What we recommend, if you want to get enough aerobic points to get aerobic benefits, is see if you could swim 800 yards, roughly half a mile, in 20 minutes or less, four times a week. That would give you aerobic benefits.

If you wanted to get health and longevity benefits, which is almost as good as being aerobically fit, you could swim 500 yards in less than 16 minutes, four times a week, and get the same benefit. You should use the stroke that enables you to swim the required distance in the required time. If necessary, this does not have to be continuous swimming, but collectively, you should cover the distance in the time goal.

In my book, Aerobics Program for Total Well Being, we have 41 different exercises that qualify as being aerobic. The top five we've evaluated are these:

  1. Cross country skiing
  2. Swimming
  3. Jogging or running
  4. Cycling
  5. Walking

Just about anyone, regardless of age or sex can get at least health and longevity fitness, if not aerobic fitness, in one of those ways.

Member question: I don't do much exercise. Is it useful if I only play tennis at my age, 54?

Cooper: According to the Surgeon General in 1996, he said the collectively, we need to get 30 minutes of some type of activity most days of the week. That can include tennis, but tennis, because of its start-and-stop nature, does not give you the same benefit, in the same period of time, as with continuous activity. If you play doubles tennis, it's going to be even harder to get enough aerobic activity to get benefit. That is why most professional tennis players jog to keep in shape. Because it's awfully hard, unless you're a professional tennis player, to get aerobic benefit strictly from playing tennis.

Member question: My 15-year-old has football training camp next week. What can I do to help him stay safe while being so active?

Cooper: First of all, it's going to take 10 to 14 days to become acclimatized during the heat. If he's not already acclimatized the intensity of exercise should be reduced.

But, beyond that it's strongly recommended that you:

  • Drink fluids before you get thirsty. Thirst is not a good indicator of either dehydration or fluid needs.
  • Two to three hours before the activity drink approximately 20 ounces of fluid, like Gatorade.
  • During the activity, drink to match the sweat loss. Average sweat loss during exercise on a warm day can range from 24 to 32 ounces per hour.
  • After the activity, consume 20-24 ounces of fluid for every pound of body weight loss resulting from exercise. So, weigh before the workout and after the workout to be sure fluid compensation is adequate.

Also, recognize the warning signs of dehydration:

  • Dry lips and tongue
  • Headache
  • Nausea
  • Muscle cramping
  • Weakness
  • Dizziness or exhaustion
  • Concentrated or dark-colored urine

If these symptoms occur:

  • Immediately stop all exercise
  • Rest in a cool place
  • Drink fluids

One thing I've noticed, if you rely strictly on water, when these teams are beginning to practice football in the late summer, the athletes will not drink as much as they need, as they would if they were drinking something like Gatorade. Because drinks like Gatorade, which are lightly flavored and contain the right amount of sodium, encourage people to drink up to 90% more than plain water, and provide one of the best choices to help you stay properly hydrated.

Member question: Is it better to wear a head covering such as a hat during outdoor exercise or work to protect against the direct sunlight, or to go uncovered for maximum ventilation?

Cooper: Without question. If you are exposed directly to the sun's rays when jogging, in competitive sports, walking, etc., always wear a hat.

The head is a prominent place to lose heat, but also to gain heat. I would be much more concerned about the harmful effects of the direct sun on the head without a hat than I would be with what you'd lose covering the head as far as being able to dissipate heat.

You need to dress as lightly as possible, but you also need to avoid sunburn. If you are going to be exposed longer than 15-20 minutes out of doors, you should use a sunscreen of at least a rating of 20 to 30. For long periods outdoors, sunbathing, it's mandatory that you use sunscreen. Even if you are at the beach and it's overcast, you need sunscreen. Or if you are next to the water under an umbrella, you still need sunscreen. The indirect rays can be as damaging as the direct rays. Without question, skin cancer is the single most common cancer that we have in America. It is early always as a direct result of exposure to the sun.

Another important point, particularly for the athletes, is if you don't have the time to acclimatize for 10-14 days, you should progress slowly into your program. If you are a regular exerciser, try to avoid the intense heat of the middle of the day. In other words, exercise before sun up, and after sun down.

Also, try to be at least 60-100 feet away from a heavily traveled highway, particularly if you are required to exercise during the heat of the day, because the air pollution that is so common in our cities hovers over a busy highway like an umbrella, extending at least 30- 60 feet outside the road. Avoid that area. So many people jog on sidewalks during the heat of the day.

Member question: When it is this hot. I start to sweat right away. Does that mean I'm burning more calories working out in the heat?

Cooper: Yes. If you do add exercise to heat, you will expend more energy. If you start sweating immediately after starting to exercise, that's a classic example of being acclimatized to heat. The earlier the onset of sweating, and the more you sweat, the less likely you are to suffer heat illness. But remember that men sweat, women glow. Why? Because the core temperature of a woman must be about 1.5 degrees higher than a man before she starts sweating. It may take her longer to acclimatize to heat, and she may be more susceptible to heat illness. So keep that in mind, ladies.

Member question: Does it place extra strain on the heart to work out in the heat?

Cooper: If you exercise in the heat, because of the acceleration of the heart rate that occurs just with heat exposure, and you add to that the acceleration of heart rate with exercise, we call that a synergistic effect, or one plus one equals three. That means you get more caloric expenditure, but also much more stress on the heart. That's the reason we say that people that have heart disease of any type should avoid vigorous exercise in the heat. Even when acclimatized I still say avoid vigorous exercise in the heat if you are suffering from heart disease.

Moderator: Dr. Cooper, before we wrap up for today, do you have any final comments for us?

Cooper: We did studies years ago when I was at Lackland Air Force base in San Antonio, Texas. I was in charge of training air force recruits. We had several deaths that occurred during basic training among young men who had come to the hot humid environment from the northern states and had no heat acclimatization. We did studies that looked at the rectal temperature before and after running two miles. It was not uncommon to have temps rise from 98.6 to 105 and 106 degrees. Those men, after the run, would either lower their temperature rapidly, or have a heat stress problem.

We developed a series of flags based upon the heat index that combines humidity, dry bulb temperature, and wet bulb temperature with ambient temperature. From that index we developed four flags: Green, yellow, red, and black. All outdoor activities were canceled in a black flag situation, and we had no further problems with heat stress.

Any football team exercising in the heat should use that same guideline that we developed in the Air Force, which essentially solved our problem. You can check with the weather bureau to get that index, and you can get the categories there.

Moderator: We are out of time. Thanks to Kenneth Cooper, MD for sharing his expertise with us again today. And thank you members for joining in the discussion.

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