Scientists who have studied exercise have found that what you eat before, during and after workouts is crucial to maintaining your health, getting into shape and staying fit. To achieve your best athletic performance without getting injured or sick depends on optimum nutrition. When you carefully plan what to feed your exercised body, it rewards you by feeling and looking better.

Short 'n Sweet
If you thought long exercise sessions were the only ways to get decent exercise benefits, take notice: small doses of exercise during the week can go a long way. " The important thing, apparently, is just do it," says Howard D. Sesso, ScD, author of an American Heart Association study on exercise and heart disease. In his study, exercisers demonstrated that several short sessions of exercise were as good for the body as a single long session (Circ 8/00; 102:975-80). " Short sessions lasting 15 minutes long appear to be helpful,"Dr. Sesso explains. Even walking about three miles per week, which is a moderate level of exercise, lowers your risk of heart disease by 10%.

No Sweat?
Some people glorify in working up a sweat; others curse the dampness. But putting in extra effort in even short bursts of activity pays off: experts have found that intense exercise burns more calories than more relaxed sessions, more effectively reduces your risk of cardiovascular disease and helps stabilize blood sugar levels. In addition, it stimulates production of human growth hormone, which offsets some of the effects of aging (Exp Biol Med 2004 Mar; 229(3):240-6).

But don't go crazy if you haven't worked out in a long time. The intensity of the workout should match your physical fitness.
According to the American Heart Association, when people exercise at a comfortable pace, their heart rate and level of exertion stay within a safe range, but still high enough to benefit their health. Strenuous activities, for those who can handle them, produce the most physiological bang for the jog. But brisk walking within your own level of fitness still offers significant benefits.

Feeding Your Muscles
When you exercise, you work and develop your muscles, which are made primarily out of protein. Despite this fact, many exercise experts have advocated high-carb diets for athletes. But, as John Ivy, PhD, and Robert Portman, PhD, point out in their book The Performance Zone (Basic Health), "[While] there is no doubt that aerobic athletes require more carbohydrate than strength athletes...we are now discovering that the addition of protein to a carbohydrate supplement offers significant benefits to aerobic athletes."

That is why researchers believe that consuming plenty of protein along with carbohydrates offers the best fitness benefits. Protein helps fuel activity more efficiently and aids in recovery after a session at the gym, allowing your body to repair muscle damage and build up muscle fibers.

During exercise, you break down muscle tissue. It is during recovery, after your exercise session ends, that muscles are rebuilt. At the same time, other cellular processes take place that adapt the body to working out.

According to Ivy and Portman, timing your intake of nutrients after exercise is crucial: "The ability of the muscle machinery to regenerate itself decreases very rapidly after a workout, so that the nutrients consumed more than 45 minutes after exercise will have far less impact in helping the muscles regenerate than nutrients consumed earlier."

Stresses and Tears
Engaging in athletics can cause microscopic muscle tears. These tears can cause a range of problems that, when you exercise excessively, can cause pain and injury.

Inflammation is the body's response to cellular damage. The damaged area can swell as the body sends white blood cells and other cells to repair the injured area. Unfortunately, the swelling can further damage the muscle cells.

Since inflammation can take 24 hours or more to cause the collection of cells in the injured area, it can be a day or two before the resulting muscle soreness reaches its peak painfulness and then starts to subside.

Cortisol, a hormone produced when you exercise strenuously, which can result in muscle fiber damage. Cortisol boosts protein breakdown, so it can be used to fuel muscle movement. But the more protein breaks down, the more potential exists for muscle fiber injury.
Free radicals are caustic molecules that are created when the mitochondria (small structures in cells) create energy; these marauders can also cause microscopic shredding of muscle strands. As you increase your use of energy during exercise, you simultaneously increase the production of free radicals. This collection of free radicals can outstrip the body's antioxidant defenses, leading to extensive muscle damage and dampening of the immune system.

All of these cellular events can make you sore. They are also the reasons that athletes who overdo it day after day are liable to come down with nagging colds and a variety of infections.

Muscle Fuel
Your muscles use different substances for fuel depending on what you ask them to do. Lift a heavy weight and muscles recruit two processes called the creatine phosphate system and glycolysis to generate a large amount of quick energy. These are known as anaerobic types of energy production.

But if you jog, swim, bike or perform any other aerobic activity, the cells use oxygen in what is called cellular respiration to supply energy to working muscles.

When you exercise aerobically for extended periods of time, the energy available is generally limited by how much oxygen your body is capable of taking in and supplying to the muscles, where it takes part in energy production. In athletic circles, this upper limit is known as your VO2max.

The carbohydrates your body burns for energy during aerobic activity are taken from blood sugar and carbohydrate reserves called glycogen. (The muscles store glycogen, as does the liver.) During a workout session, your glycogen supply is limited to what is stored with your muscles. But blood glucose can be boosted by carbohydrate drinks, energy gels or bars.

Most people who work out have enough glycogen and blood sugar to fuel moderate aerobic activity for about two hours. After that, the body turns mostly to fat and protein stores to fuel exercise.

Fat Into the Fire
In contrast to the body's quickly diminishing supply of glycogen and blood sugar, fat can last for hours and hours of exercise. According to Portman and Ivy, a 200-pound man with 15% body fat has, theoretically, enough fat energy to run from Washington DC down to Miami Beach-and still has enough energy left over to jump into the ocean.

But using fat for energy is complicated; fat is stored in fat tissue and not readily available to working muscles. Plus, to burn fat for energy, the body needs carbohydrate-it cannot burn fat all by itself. What's more, the conversion of fat into energy doesn't go as quickly as carb conversion.

Protein is also used for energy when carbs run low. But the more you use protein for energy, the more you risk soreness as muscle fibers break down.

Prepare to Energize
To maximize your energy during exercise and minimize soreness, Portman and Ivy recommend some simple nutritional steps:
• Drink 14 to 20 ounces of water or a sports drink with electrolytes about a half hour before you work out. Consuming fluid helps stave off dehydration longer, helps you sweat more (which cools your body) and moderates the rise in body temperature that takes place during exercise. Portman and Ivy favor sports drinks to help you retain fluid and maintain your mineral balance.
• Eat carbohydrates an hour before exercising, which boosts glycogen and increases blood sugar and insulin. Portman and Ivy add that, alternatively, you can also consume a protein/carbohydrate sports drink about half an hour before working out. The protein helps protect muscle protein from being broken down.
• Drink small amounts of fluid frequently as you exercise to replace water lost through sweating. While some experts recommend only drinking enough to quench your thirst, most researchers agree that a sports drink with electrolytes is best to ensure proper mineral balance in your body.
• Consume carbs and protein during exercise. Portman and Ivy note that soccer players who consume sports drinks that contain electrolytes, carbohydrates and a bit of protein can perform more effectively. Cyclists who go on bike rides of three hours or more enjoy more endurance when they eat energy bars or consume other sources of carb and protein. Portman and Ivy advocate drinks that contain carbs and protein in a 4:1 ratio.

Limit Soreness
Taking protein and carbs while working out can limit muscle damage and curtail soreness. Carbs apparently drop your cortisol levels, and thereby limit muscle injuries linked to this hormone. While the mechanism that helps protein limit muscle soreness is not completely understood, it is possible that taking in protein while working out keeps the body from shredding muscle tissue in search of fuel.

Supplements that contain antioxidants such as natural vitamin E and vitamin C (Portman and Ivy think you should take these during exercise) may limit free radical damage to muscle fibers.

Muscle Reconstruction Plan
If you want to help your exercise plan make you stronger, you should focus your after-exercise sports nutrition plan on these steps:
• Help your muscles recover from damage during activity and stimulate the rebuilding process
• Replace glycogen (carbohydrates) the muscles have used up during your workout
• Reinforce your immune system
• Replace water and minerals lost in sweat
Even after you stop exercising, your muscles are still breaking down, according to Ivy and Portman. The key to putting the brakes on this breakdown and initiating the rebuilding process is by consuming a combination of protein and carbohydrate within 45 minutes after your workout is completed.

The protein part of the equation is vital: don't merely indulge in only carbs after exercising. A recent study found that while carbs could help muscles rebuild, adding protein can make a big difference in improving your fitness (J App Phys 2/04).

This combination of nutrients stimulates the pancreas so that it releases insulin. The release of insulin is the key, initial step that sets off a cascade of physiological events that speeds muscle recovery. Although many people think of insulin as an undesirable hormone-if you never exercise, too much insulin may help drive your blood sugar down and cause other problems-for exercisers, this hormone plays a crucial function in benefiting from exercise.

By eating carbohydrate and protein soon after working out and stimulating insulin, according to Ivy and Portman, you help your body boost its synthesis of protein by:
• Increasing the amount of amino acids (protein building blocks) that get into the muscles-this can increase by up to 50%
• Increasing the production of protein synthesizing enzymes by up to two-thirds
• Slowing the breakdown of muscle proteins

Drinking for Exercise
The most obvious nutrient you lose during intensive exercise is water in your perspiration. However, that perspiration also contains an array of minerals known as electrolytes. So, for optimal performance and health, experts recommend you replace both the water and its minerals.

Merely drinking water-instead of electrolyte-filled sports drinks-during prolonged aerobic activity can be dangerous. It leaves you vulnerable to a condition called hyponatremia, which can occur when your blood levels of sodium and other electrolytes drop, but your blood volume stays steady or increases because you drink lots of water.

According to Edmund Burke, PhD, in his book Optimal Muscle Performance and Recovery (Avery), one out of four athletes who seek medical attention after a long race are suffering hyponatremia.

" Typically," he says, "conscientious athletes get in trouble because they adhere too diligently to one recommendation: the need to drink lots of fluids. They tend to ignore another recommendation: The need to keep electrolytes up...for most endurance athletes the real problem is drinking too much water." Dr. Burke warns that you can possibly suffer hyponatremia even if you don't drink a lot of water.

Signs of hyponatremia can be similar to those of heat exhaustion. But, while resting and cooling down can help alleviate heat exhaustion, that doesn't help hyponatremia. " To protect yourself against hyponatremia, start by paying attention to how much you sweat," Dr. Burke says. If your sweat seems very salty, burns your eyes or leaves an evident, white residue on your skin, you may be losing a great deal of sodium and should be diligent about eating salty foods. " You can also make sure you're getting enough sodium by drinking sports drinks instead of plain water during long (exercise) events," Dr. Burke notes.

Exercise Matters
Of course, no matter what you decide to eat or drink while exercising, the most important factor for your well-being is to get out to the gym, onto the track, or just on to the sidewalk, and do something, even if you only want to go out for a walk. No matter how old you are or what kind of shape you're in, you'll benefit from exercise.

" It's solid evidence that across-the-board declines occur when people stop exercising," says Charles Emery, PhD, professor of psychology at Ohio State University (Health Psychology 3/04).

Don't decline or remain supine. Let your fitness climb.