Calling All Athletes:
Don't Let Heat Stress Spoil Dryland Training!
By Donald M. Christie Jr., MD
NENSA SPORTS MEDICINE COMMITTEE
Those first, few warm days in April -- forget any cold rain or wet snow that followed! -- give us a sample of what awaits as we get into dryland training. It's none too soon to remember to let up a little, drink enough of the right fluids, and play it safe when it comes to training in the heat and humidity of late spring and summer.
THE PROBLEM
Heat stress challenges all athletes. Active muscles generate heat that
must be dissipated, or else! (One could argue that the ultimate limiting
factor of human performance is our inability to satisfactorily rid the
body of the heat generated during intense and prolonged exercise.) At
the least, heat stress makes us tire more easily and performance suffers.
Heat injury in its worst forms -- heat exhaustion and heat stroke -- can
be devastating, as the untimely, preventable death last summer of Minnesota
Vikings player Korey Stringer reminded us.
This necessary cooling occurs year round, chiefly through the evaporation of sweat and the dilation of skin blood vessels to radiate the heat away, a process that works quite well in cold, dry air. Upon exposure to warmer weather, the body gradually becomes acclimated to exercise in this new environment. The sweating mechanism turns on earlier during a given exercise, and the sweat produced is more dilute, containing less sodium and potassium.
This boost in cooling efficiency and conservation of important minerals takes time -- up to two weeks of gradual exposure to hot weather. To make matters worse, once the summer humidity arrives, sweating becomes less effective, if not altogether ineffective on very humid days, and thus simply dehydrates us without cooling. Compounding this problem is the difficulty radiating heat away from the body on hot days. (Think about it: If our core temperature is a fairly constant 98-99 degrees F. at rest, how much excess heat can we then radiate into a day that is already 99 F. in the shade?!)
THE SOLUTION
(Pun half-intended)
What's a poor athlete to do?! We don't have to exercise when it's really
hot and humid. We can choose early morning or evening hours for those
workouts, and not push the pace as much, hence generating less heat to
dissipate. Wear light, loose clothing -- as little as decency allows --
to promote radiation and evaporation. (Don't forget to apply sunscreen
before you go out!) Stay in the shade if possible, or find a swimming
pool for some "cross training." (If you swim in a pond or lake
for any length of time, watch out for hypothermia. Too much cooling can
be as bad as too little!) Get your workout in an air-conditioned space,
if you have access to one.
Be especially careful to replace water and electrolyte (salt) losses. If you are out for more than 30-40 minutes, you should begin this replenishment during the workout and not wait until you finish.
HOW MUCH AND WHAT KIND OF FLUID SHOULD WE DRINK?
Don't wait for thirst to remind you! Unfortunately, thirst is a late symptom
of dehydration. (If you feel thirsty, you're already "a quart low.")
During hot weather, we may need to drink over a gallon of fluids in addition
to what we get in our solid food every day! (Prove this to yourself by
noting your weight loss from sweating in a hot weather workout and doing
the math: a pound equals a pint.) Drinking plain water is fine (Poland
Spring or Evian if you must!) as long as the exercise lasts only 20-30
minutes, but for longer bouts of activity, take in a sports drink (like
Gatorade, XL-1, Extran, WARPaide) that contains salts and dilute carbohydrate
(to make it more palatable and provide some "on line" energy,
as well as avoid the problem of creating a low blood sodium level from
ingesting too much plain water over time).
During prolonged exercise, aim to drink at least 8 oz of a sports drink every 15 minutes. (Trust me. This isn't too much if you are really exercising on a warm day!) Researchers have repeatedly shown that a beverage containing 4-8% carbohydrate (4-8 grams of CHO per 100 grams of solution) is more rapidly emptied from the stomach than "stronger" solutions. (It is no accident that Gatorade is about 6% CHO.) Become a student of the "Nutrition Facts" labels and calculate carbohydrate concentration of a product. (For example, an 8 oz -- 240 ml -- serving of Gatorade contains 14 grams of carbohydrate: 14 divided by 240, converted to a percentage, equals 5.83%. Reconstituted as directed, Extran contains 4.4 grams of carbohydrate per 100 ml of solution: exactly 4.4%.)
The carbohydrate concentrations of full-strength juice and soda (typically, 10-12%) are too high to allow quick absorption during exercise, and those beverages may contain little or no sodium and potassium, so stick with the more dilute sports drinks when exercising. Juice, milk, and soda are all right to consume before and after exercise. Make your own inexpensive sports drink by mixing water half-and-half with real orange juice and adding a pinch of table salt to each 8 oz. of the mixture. The new "fitness waters" are just that: water -- with a trace of sugar and vitamins and minerals thrown in to add flavor and justify the cost! They are something to quaff only when you bore of Poland Spring, and bear little resemblance to "real" sports drinks.
Cold drinks are more quickly emptied from the stomach than warmer beverages. Avoid any great amount of caffeine and alcohol-containing drinks because of their diuretic effect (causing more water to be lost through the kidneys than you ingest in that volume of beverage). Always try out a new drink well in advance of a big race, to be sure the formula "agrees" with your digestive system. Some of the more complex sugars and other ingredients (including amino acids and whey protein contained in products such as Accelerade and Cytomax) may produce bloating, cramping, and diarrhoea in folks so destined. (These drinks are mostly dilute versions of products marketed as apres-ski restoratives and will be discussed in future papers about nutrition for training and performance.)
Whether you take a water bottle with you or use a backpack fluid tote,
come up with some way of bringing the right fluids along for the workout.
Never hesitate to seek the shade and cool down should you begin to feel
tired and weak. Don't let heat injury spoil your training at this beautiful
time of year.
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Comments? Questions? E-mail Dr. Christie at dchristie@adelphia.net.
