TRAINING IN HOT WEATHER: SAFETY AND PERFORMANCE
The most common training affects of heat stress are decreased power and coordination with increased risk of injury. Hot, tired, and sweaty are expected but ischemic heat stroke or hyperthermic organ damage are not.
Training in hot weather is difficult. You warm-up quickly but exercise is more tiring and you sweat a lot, feel weaker, and sometimes get sick. And it's common to hear about cramps, dizziness, and headaches.
Twenty times more energy is produced during training and 75% is converted to heat
You're told to drink more water and hope that's enough. But you worry about heat exhaustion. You want to be sure your training efforts get better results than simply surviving the training. Consider a homemade rehydration drink.
85% of exercise heat is evaporated until humidity passes 50%
Blood carries heat from muscles to the skin which gets red and warm. Sweating cools the skin by evaporation. High temperature and humidity decrease evaporation. Blood volume is reduced, the heart works hard, organ temperatures rise. You are at risk.
You're willing to suffer some pain and discomfort during training but we want to know the difference between the expected stress of exercise and risk of heat exhaustion: the signs, the risks, and ways to keep you from crossing the line.
Any unexpected or sudden weight loss is a serious sign of dehydration.
The bottom-line is that over a third of us are dehydrated when we start each training session and go downhill from there. There is virtually no chance for you to recover hydration during training. You're simply not going to drink as much water as you sweat ... and if you do manage the result is a likely to cause problems resulting in weakness and more cramping.
Sweat weight loss of one percent of normal body weight is typical during training and two percent causes significant performance loss. That's three pounds for a 150 lb. person ... causing a noticeable drop in strength, coordination, and endurance ... and risking cramps, nausea, weakness, dizziness, and headache.
A more obvious sign is urine: clear and regular is normal. Dark (tea-colored) and decreased volume indicate dehydration
Other signs of heat illness are weakness, clumsiness, fatigue, nausea, confusion, and headaches.
First signs of heat stress are common to most training: heavy sweating, rapid heartbeat, shortness of breath, fatigue. Without cooling and hydration these early warning signs can lead to heat cramps with muscle pain and spasms, weakness, and uncoordination.
Next stage is more serious heat exhaustion with headache, dizziness, and irritability.
Final stage is heat stroke with mental confusion, loss of control, and extremely high body temperature. The body can rapidly shut down with life threatening damage to vital organs.
Regular training during the warming season leads to acclimitization. About a week of moderate training in the heat leads to increased sweating and better cooling and two weeks of training provides real heat readiness.
Moderate training means light sweating at 50-60% exertion during the first 4-7 days building to 75% exertion for the next week and following hydration guidelines during all training.
Training heat stress starts normally with sweating and fatigue ... turns to cramps ... and finally headaches and mental confusion.
Mental confusion, fainting, or fainting are dangerous signs for emergency treatment.
In Exhaustion you'll notice your own headache ... other people will have to trust your judgement to stop training.
In Stroke you'll notice someone else's clumsiness or irritability ... you may have to stop their training ... and call 911 if they are confused or pass out.
YOUTH RISKS: Kids are not small adults. Their physiology is different
They heat up faster and don't sweat as much so they don't cool-off very well. During summer weather, hot and humid, they are at greater risk of heat exhaustion.
Two-thirds of teenage athletes are dehydrated at the start of each training session. Then they start working and generate more heat from exercise than adults, sweat less, and drink less.
"Active children are more likely to suffer from headaches, dizziness and cramps, which are key symptoms of dehydration."* In fact, one out of five teenaged athletes begin their training seriously dehydrated.
"None of (these) kids were able to regain healthy hydration status during the practice."*
Most teenagers produce a half quart of sweat every hour during exercise in hot weather (82 degrees with 50% humidity on a nice summer day in NYC).
Suggested guidelines for coaches and youth leaders are to provide a 10 minute rest break every half hour of exercise during moderate heat and every 20 minutes when the temperature goes over 90 degrees or humidity over 60%.
One suggestion is for kids to drink at least 4.5 ounces of water every half hour for each 18 pounds of body weight during training. But that doesn't make up for initial dehydration.
Summer training must have scheduled breaks and include hydration
This is not just rest but directly observed drinking before, during, and after activity.
*ACSM Health & Fitness Journal May/June 2005
HOMEMADE REHYDRATION DRINK
Re-hydrate with a combination of water (fluid ... replace sweat), carbohydrate at 6-8% concentration (energy ... think sugar), and electrolyte (sodium and potassium ... think salt or lite salt).
"Pinch and scoop" * measures eqivalent to classic Gatorade®
* Pinch is thumb and one finger.
Consult with a healthcare professional before using this information or if you have symptoms or medical conditions which might be affected by using any product or procedure discussed.