Great Tips on the Physiology of Running
It provides some great insight into training and racing at high temperatures for a half marathon or beyond. Here are some great excerpts...
When it is humid, sweat does not easily evaporate, so the body sweats even
more. Blood volume drops, and the body has to make a choice: divert blood to the
skin for cooling or divert it to the muscles for performance. It sends blood to
the skin.
The result is predictable, Dr. Martin said. With less blood going
to the muscles, the runner slows down or stops. The challenge, then, is to find
the fastest pace that can be maintained for 26 miles. Go too fast and you may
collapse before the race is over. Go a little slower than you have to and you
may lose the race.Of course, he added, runners should not use lotions, including sunblock, because they add a barrier to the evaporation of sweat. He said that while it seemed logical to drink as much water as possible before the race — and runners try it — “it doesn’t work.” The reason, he explained, is that drinking a lot of water increases blood volume and the body responds by getting rid of it, in urine.
“What you need to do is to increase your total body fluids another way,” Dr. Martin said.He added that the legal, safe way to do it is through glycerin loading. The technique exploits the unusual properties of glycerin, a thick, gooey sugar alcohol that is sold in drugstores as a lubricant. Each molecule of glycerin absorbs three molecules of water. During a race, the body uses the glycerin for energy. And every time the body metabolizes a molecule of glycerin, “it unleashes three molecules of water,” Dr. Martin said.
The result, he said, is that “you have a water bank account.In a recent study, they recruited 60 college athletes. Thirty were told to eat three high-carbohydrate energy bars a day, in midmorning, mid-afternoon and after dinner. The others got packets of a sweet powder to mix with water and drink three times a day. The athletes thought the study was comparing liquid to solid snacks. In fact, the powder contained no calories, and each energy bar had 250 calories. No one gained or lost weight; those eating the energy bars unconsciously adapted to the extra calories by eating less at other times. But the athletes who ate the energy bars lost nearly 2 percent of their body fat, a statistically significant change, and greatly improved their performance on a 30-second test of anaerobic power and endurance.
