To be able to exercise intensely in hot weather, you have to maintain water, sugar and salt in your body for the entire time you exercise. How fast you can ride, run, or exercise is limited by the time it takes to bring oxygen into your muscles. If you can increase the oxygen supplied, or decrease the oxygen needed, you can move faster. Since sugar requires less oxygen than fat or protein to power your muscles, anything that allows your muscles to burn more sugar and less fat will help you to move faster.
Salt is necessary to hold water in your body, prevent muscle cramps, and help keep your muscles contacting with great force.
Carbohydrate loading is out: In the old days, athletes used to follow a dietary and exercise maneuver called "carbohydrate loading". This outdated maneuver was based on the fact that the more sugar an athlete can store in his muscles before competition, the more sugar his muscles will burn and the faster he can go. Seven to four days before competition, an athlete eats a diet low in carbohydrates. This depletes his muscles of stored sugar and increase the ability of his muscles to store extra sugar. Four days before competition, he reduces his workouts and eats his regular diet plus extra carbohydrates. Athletes do not do that any more because they can maximally load their muscles with stored sugar just by cutting back on their workload and eating their regular diets plus a little extra carbohydrates.
The key to the precompetition diet: Athletes have to be careful about taking in lots of extra calories during the week before competition because all extra calories, including those from carbohydrates, are converted to fat which is stored in cells in your body including muscle cells. The first sugar that enters muscles can be stored as muscle sugar called glycogen. When muscle glycogen stores are full, all extra sugar is either used for energy or stored as fat called triglycerides inside muscles.
Extra fat in muscles blocks insulin receptors to prevent muscles from responding normally to insulin. This reduces the amount of sugar that can get into muscles, causing muscles to run low on sugar. Muscles then burn less sugar and a greater percentage of fat and the athlete has to slow down.
To be at his best, an athlete should load his muscles maximally with stored sugar called glycogen and not store extra fat in muscles. The best way to do this is to eat a regular diet with a little extra carbohydrate (that forms sugar) and take in extra sugar during competition to keep up sugar stores.
Precompetition meal: Eat anything you like as long as your meal contains extra carbohydrates and salt. All carbohydrates are either single sugars or combinations of sugars. Salt is necessary to hold extra water to help prevent dehydration caused by heavy sweating during hot-weather competitions.
Before I race, I eat a hard boiled egg plus a grapefruit. You can eat whatever you prefer.
During your event: It is far more important to take extra sugar during a competition lasting more than two hours than anything you do before your event. The limiting factor to how fast and intensely you can exercise in events requiring endurance depends on how quickly you can get sugar into muscles during exercise. You can markedly improve performance in endurance sports by starting to eat and drink soon after you start exercising.
Do not take in sugar until at least five minutes after you start your competition: When you eat sugar and your muscles are not contracting, you get a high rise in blood sugar that causes the pancreas to release large amounts of insulin. This can cause a drop in blood sugar levels that can tire you. On the other hand, exercising muscles draw sugar rapidly from the bloodstream without needing insulin. So taking sugar during exercise usually does not cause the high rise in blood sugar levels that causes your pancreas to release large amounts of insulin.
The energy for your brain comes almost exclusively from the sugar in your bloodstream. When blood sugar levels drop, so do brain levels and you feel tired and have difficulty coordinating your muscles.
Another reason why you have to take sugar during intense exercise is that there is only enough sugar in your bloodstream to last three minutes at rest. To maintain blood sugar levels, your liver constantly releases sugar into your bloodstream. But there is only enough sugar in your liver to last about twelve hours at rest and far less than that when you exercise. When muscles run out of their stored sugar supply, it hurts to exercise and the muscles become difficult to control.
Don't wait to feel hungry: Hunger during exercise is a very late sign of not getting enough calories. By the time you feel hungry, your body will be so depleted of sugar that you will have to eat large amounts of carbohydrate-rich food just to restore your sugar supplies.
What to eat and drink: All carbohydrates are single sugars, or sugars bound together in twos, up to thousands and millions. Before any carbohydrate can be absorbed into your bloodstream, it must first be broken down into single sugars. Human intestines do not permit combination sugars to pass into the bloodstream, so the most effective way to increase endurance is to take sugar- containing foods and drinks during prolonged exercise.
Caffeine increases sugar absorption from the gut. Taking caffeine when you eat carbohydrate-containing foods and drinks can double your rise in blood sugar (Journal of Caffeine Research, April 16, 2011). A high rise in blood sugar causes all the horrible side effects of diabetes: blindness, deafness, heart attacks, strokes and so forth. However, during exercise, caffeine can increase endurance (Medicine & Science in Sports & Exercise, July, 2010) by increasing the absorption of sugar from your intestines and by increasing the uptake of sugar by your exercising muscles by as much as 26 percent (Journal of Applied Physiology, June 2006). Caffeine is found in coffee, tea, chocolate, and cocoa.
CAUTION! Take caffeinated sugared drinks only when you exercise. Taking sugared drinks, with or without caffeine, when you are not exercising causes higher rises in blood sugars that increase risk for diabetes and cell damage.
Salt: The only mineral that you need to take during prolonged exercise is sodium, found in regular table salt. Potassium, calcium and magnesium deficiency do not occur in healthy athletes (Medicine & Science in Sport & Exercise, October 1999). Just about everyone agrees that you need to take in drinks and foods containing extra salt during extended athletic competitions in hot weather. Not everyone agrees that athletes need to take in extra salt at rest. If you don't take salt and fluids during extended exercise in hot weather, you will tire earlier and increase your risk for heat stroke, dehydration and cramps. You can drink special electrolyte drinks, or eat salted foods along with any fluid during competition.
Eating and drinking during hot weather competition: When you compete in hot weather, chose the drink that you like best as you are more likely to drink more of drinks that taste good. You also need sources of sugar and salt. You can get sugar from drinks or food. You can meet your needs for sugar and salt by drinking water and eating sugared whole grain bars or fruit pastes and heavily salted potato chips or peanuts. You can also get your sugar from a sugared drink of choice and your salt from any salted foods. Salty drinks usually taste awful, and salt pills often irritate the stomach, so most athletes have to get their salt by eating salted foods.
How much should you drink? As I wrote above, you will not become thirsty during exercise until you have lost between two and four pints of fluid, so you can't wait for thirst to encourage you to drink. Dehydration makes you tired and it is unlikely that you can replace the lost fluid during a race after you have become thirsty. The American College of Sports Medicine recommends a limit of 1200cc (5 cups, 2.5 pints, a little over 1 quart, or 2 average size water bottles) per hour, but for a person who is not exercising near his or her maximum, this could be too much (Clinical Journal of Sport Medicine, July-August 2005). A person exercising near his capacity and not slowed down by fatigue probably does not have to worry about limiting fluid intake. He is working so hard at maintaining intensity, he doesn't have enough time to drink too much. On the other hand, people slowed down by fatigue or those who are out of shape should limit fluid intake, probably to less than two large water bottles per hour. When you exercise for more than an hour, particularly in hot weather, you need fluid, salt and sugar. We drink Pepsi Cola and eat salted peanuts.
Hyponatremia - Drinking too much fluid: On very rare occasions, drinking too much fluid causes death from a condition called hyponatremia. It almost always occurs in people who attempt events that are beyond their training levels. They run out of energy, slow down and expend more effort drinking fluids than in maintaining their pace. This condition is caused by drinking too much fluid, not by excessive loss of salt in sweat or by the stress of exercising. The extra fluid expands blood volume and dilutes blood salt levels. This causes blood salt levels to drop to low levels, while brain salt levels remain normal. Fluid moves from an area of low salt concentration into areas with high salt levels, so fluid moves from the bloodstream into the brain, causing brain swelling. Since the brain is enclosed in the skull, which is a tight box, the brain expands and has nowhere to go, so it is squashed to cause headache, nausea, and blurred vision. Since these are the same symptoms caused by pure dehydration with normal blood salt levels, the only way to diagnose the condition is with blood tests. As blood salt levels drop even lower, the person becomes confused, develops seizures and falls unconscious. You should suspect hyponatremia when the event takes more than four hours and the athlete has been drinking often during the event. All people who are confused, pass out or have seizures should be sent to a hospital immediately. Hyponatremia requires skilled management because the first impulse of an inexperienced physician is to give intravenous fluids, which dilute blood salt levels further, causing more brain swelling that can kill the patient.
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