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Sunday, March 6, 2011

Got Carbs?

Thanks to recent research revealing the true power of glycogen, or carbohydrates stored in muscle tissue, the question is no longer whether to eat carbs, but how much to take in for your level of activity. Too much and your body converts the excess to fat. Too little and you won't have enough fuel for endurance sports.

Over the past two years, researchers at the University of Cape Town have determined that glycogen acts as a helpful communicator between your muscles and your brain. When you start to exercise, it sends signals to your cerebral cortex, telling it how long and how intensely you should work out. Based on this info, the brain then sets your pace.

This process was first observed during a 2004 study in which researchers determined that cyclists set the intensities of their one-hour rides within the first 120 seconds of their efforts—before any fatigue had set in or significant glycogen stores had been burned. The established intensities, scientists discovered, were directly proportionate to the amount of glycogen stored in the cyclists' legs prior to working out. "Additionally, we found that lower glycogen concentrations cause the brain to increase sensations of fatigue dramatically," says Tim Noakes, a professor at the Research Unit for Exercise Science and Sports Medicine at the University of Cape Town.

The lesson here is simple: To perform at your best during long hikes, rides, and runs, you have to keep your glycogen levels high by eating enough carbs ahead of time. For the Weekend Warrior it's as easy as upping fruit and bread intake before a big outing. But for the Daily Grinder, who trains for an hour or more each day, it gets complicated: Research tells us that, to stimulate your muscles to adapt and use oxygen more effectively, you occasionally want glycogen levels to bottom out. To get the correct amount of fuel at the optimal time, stick to these strategies.


Fuel up. If you work out nearly every day for an hour or more, it's likely that you're not getting enough carbs to boost your glycogen depots and improve your performance. As a rule, hardworking athletes should get 70 percent of their calories from carbs, taking in four grams of carbs per pound (half kilogram) of body weight a day. That's 640 grams of carbs for a 160-pound (73-kilogram) athlete. But you can't just stuff down 42 slices of wheat bread in one sitting. Glycogen is finicky and best stored in the 30-minute window immediately following your workout. During this period, consume 25 percent of your daily carb intake.

Empty the tanks. To properly diminish your glycogen levels, incorporate longer-than-usual workouts into your program. If, for example, you ordinarily work out for about an hour each day, strive for one 90-to-120-minute session a week.


Fuel up. If you save your hour-long workouts for the weekend, your carb-intake strategy is a bit more complex. Like the Daily Grinder, you'll want to get about 70 percent of your total calories from carbs, but from Monday to Thursday your daily carb intake should be limited to between two grams per pound of body weight (if you rarely work out) and three grams per pound (if you work out for 30 minutes on most weekdays). On Friday stock up for weekend pursuits by eating the same four-grams-per-pound feed bag as the Daily Grinder. Ditto on Saturday. By Sunday, however, you should scale back your total carb consumption to midweek levels in anticipation of the more sedentary workweek. A note of caution: Your weekend pursuits may leave you ravenously hungry on Sunday evening. Fill up on good carbs—whole grains, fruits, and vegetables—not empty calories.

Empty the tanks. You're already depleting your glycogen levels with semiregular activity and lower carb consumption during the week.

Source: National Geographic

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