Fitness

Don't Bonk! When Your Workout Stops Working Out

(CBS 5) Don't bonk.

It's a workout no-no; in athletic circles, something to be avoided at all costs. When bonking hits you during exercise or in a sports event, you get lightheaded, lose your focus and your body slowly, inexorably grinds to a painful halt. Here's how to prevent the dreaded "bonk" to boost your workout efficiency and enjoyment!

The phenomenon earned its name in the late 1980s. Marathon runners, of all levels, reported "hitting the wall," at mile 20 of the 26.2 mile contest. Research later verified that those people were simply running out of muscle glycogen, the body's primary energy source during any physical activity.

While most of us don't run the risk of hitting the wall in our daily exercise routines, we've all had less-than-stellar workouts and wondered why. By making slight alterations to how and what you eat before, during and after exercise, you can enjoy workouts more, reap greater benefit from that exercise time and recover more quickly.

To begin, you need extra carbohydrates to provide the fuel for exercise and recovery; and vitamins and minerals to help convert those carbohydrates to usable energy and protein for adding new muscle. Plus you need some fat to keep cell membranes healthy and to produce important hormones. The best way to meet these nutritional needs is not with a gym bag full of energy bars and Gatorade. It's with a balanced diet, fine-tuned for your exercise goals and caloric needs.

Your body's main fuel currency is a substance called adenosine triphosphate, or ATP for short. All fuel -- carbohydrates, fats and proteins -- need to be converted to ATP before they can be burned for energy.

During rest, the body gets slightly more than half of its ATP from fatty acids, and the rest from carbohydrates, along with a small percentage of amino acids from protein breakdown.

During physical activity, the body adjusts its mixture of fuels. Your muscles never use just one single fuel. How much of which fuels they use during exercise depends on the duration and intensity of the activity, and the degree to which the body is conditioned to perform that activity.

During exertion, glucose that is stored in the liver and muscles as glycogen is released into the bloodstream. Your muscles use both of these glycogen stores to fuel their work. When glycogen is depleted, the muscles become fatigued. Glycogen depletion usually occurs about two hours after the onset of intense activity -- which coincides, for most people, with mile 20 in the marathon.

Studies have confirmed that high-carbohydrate diets enhance endurance by enlarging glycogen stores. In one study, runners eating a diet high in fat and protein and low in carbohydrates had a maximum endurance time of 57 minutes; those eating a diet of about 50 percent of calories from carbohydrates lasted 114 minutes; and those eating a high-carbohydrate diet (83 percent of calories) were able to run for 167 minutes.

You want to feel energized, not tired, going into a workout, so you can get the most benefit out of your hard work. I've found that the best way to do that is to have a snack one to two hours before working out. This allows you to start your workout with enough glucose in your bloodstream to get you going and keep you going without feeling weak or shaky. The snack should be 200 to 300 calories (but may go up to 400 calories depending on your daily calorie intake) and should provide mostly carbohydrates, along with some protein or fat. Some ideal snacks that fit the bill: energy bars, crackers and peanut butter, raisins and nuts, yogurt, or half a turkey sandwich.

You should also make a point to drink water before you begin, especially if it's hot outside. Three cups of water is about right. If your body becomes dehydrated by as little as 2 percent, you can lose up to 10 percent in performance, because a lack of water actually makes it harder for your blood to deliver oxygen to your muscles.

Coffee provides a good pre-workout pick-me-up and can improve endurance by mobilizing free fatty acids in the bloodstream. But don't count coffee as part of your daily water intake; the caffeine in coffee is a diuretic.

During your workout, the general rule of thumb is to drink before you feel thirsty because you can lose up to 2 percent of your body weight as sweat or urine before your thirst mechanism sets in. As for fuel, consume 300-500 calories, either as a sports drink or easily-digestible food, for every hour of exercise.

TIP: If you push beyond a certain level of exertion too many times during a workout, no matter how impeccably fueled you are, you will run out of gas. It's simple physiology. That's why it's important to exercise smart. The best way to do this is to monitor your heart rate. By keeping your heart rates lower throughout the workout and pushing when you need to, you can reap all of the fitness benefits without running out of steam.

Right after exercise or an athletic event, immediately drink at least two cups of water to rehydrate your body. And, depending on how hard and how long you went, eat a carbohydrate-rich snack to replace the glycogen stores you likely used up during your exercise; the sugar and carbohydrates will help you recover more quickly so that you can come back in your next workout feeling great.

So, what to eat after your workout? A bagel with jam, a fruit smoothie, cereal -- or in my case, two to three heaping spoonfuls of Ben & Jerry's Chunky Monkey ice cream! That leads to my final tip: If you're going to have the sweet stuff, have it after your exercise…and relish every bite. You earned it!

Eric Harr is the CBS-5 "Weekend Early Edition" fitness expert, a best-selling author and the Founding Editorial Director of VIV, the first celebrity-driven fitness magazine set to launch in June.

(© MMVI, CBS Broadcasting Inc. All Rights Reserved.)