Which Comes First, Cardio or Weights_ - Alex Hutchinson [85]
How to get one gram of carbohydrate and 0.3 grams of protein per kilogram after exercise
• For a 120-pound person
• A tuna sandwich and a 16.9-ounce sports drink
• A cup of oatmeal with milk and an 8-ounce sports drink
• For a 175-pound person
• A protein sports bar and a 25-ounce sports drink
• Spaghetti with lean meat sauce and a cup of low-fat milk
How much should I drink to avoid dehydration during exercise?
It’s the first lesson you learn about exercising in the heat: if you don’t drink enough, you’ll get dehydrated, and that will force you to slow down. By the time you feel thirsty, we’re told, it’s already too late. But some exercise physiologists, led by South African researcher Tim Noakes, have reached an alternative conclusion. It’s not being dehydrated that actually slows you down, Noakes argues; rather, it’s letting yourself get thirsty that signals to your brain to put the brakes on.
The idea that drinking according to thirst isn’t enough to replenish your sweat losses is supported by plenty of research. For example, a 2007 study by researchers at the Gatorade Sports Science Institute found that experienced runners who were allowed to drink as much as they wanted during a 75-minute run replaced only about 30 percent of the fluid they lost by sweating. The conclusion the Gatorade scientists drew from this study is that we should plan to drink much more than thirst alone dictates—but Noakes disputes this interpretation.
The initial studies linking dehydration with impaired performance date back to World War II, as researchers sought to give U.S. military forces fighting in desert or jungle conditions an edge over their enemies. Since then, dozens more studies have shown that if you dehydrate someone (by administering a diuretic, for example), their exercise performance will suffer. Similarly, when subjects aren’t allowed to drink during prolonged exercise, their performance is decreased. Based on these studies, researchers concluded that sweating out more than about 2 percent of your total body weight will slow you down.
But the subjects in all these studies are not just dehydrated; they’re also forced to become thirsty. None of the studies show that subjects who drink freely according to thirst (and thus fail to replace their sweat losses) perform any worse than subjects who drink enough to replace all their sweat. Both thirst and the slowdown that eventually follows are the body’s way of protecting itself in advance from damaging dehydration, Noakes argues. The flaw in the conventional studies is illustrated by a 2006 study in which subjects were told in advance whether or not their fluid intake would be restricted during a 50-mile cycling trial. When they knew they wouldn’t be able to drink freely, the subjects biked more slowly right from the start of the trial, long before any physical effects of dehydration could have had an impact.
In Noakes’s “central governor” theory (see Chapter 3), the brain monitors signals from various parts of the body with the goal of reducing exercise intensity before the body is in any danger of damaging itself. As fluid levels drop—but before they reach the point at which performance would be compromised—the central governor responds by initiating thirst and reducing intensity. In this picture, you won’t slow down unless you actually feel thirsty, no matter how much fluid you’ve lost. Studies of endurance athletes show that the thirst mechanism varies greatly between individuals: some drink very little during races, while others drink a lot. Interestingly, the fastest finishers tend to also be the most dehydrated—a finding that lends support to Noakes’s argument.
Until a few years ago, few researchers paid attention to Noakes’s ideas. But the potentially fatal dangers of drinking too much—which were first pointed out by Noakes in the 1980s but ignored for nearly two decades—have caused a re-evaluation of hydration guidelines. Most authorities still recommend aiming to limit sweat losses to less than 2 percent of your body weight, but the