Physical performance depends on multiple factors:
- Endurance: length of time a given level of activity can be maintained, or resistance to fatigue;
- Aerobic capacity: ability to perform despite symptoms of shortness of breath;
- Pain threshold;
- Body hydration;
- Temperature control.
Physical training maximizes physical performance, and quality practice equals improvement. To achieve maximum benefit of training, proper diet is required. A high-quality sports diet must:
- Fuel the muscles for top performance;
- Nourish the body;
- Contribute to current health and future of longevity.
To satisfy these requirements, the body must have energy, provided by:
- Calories and healing capacity, in the form of carbohydrate, protein, fat;
- Other nutrient/enzyme systems, in the form of minerals and vitamins;
- Circulation to muscles (for nutrients, water, and oxygen).
Athletes should eat a 60-70% carbohydrate diet daily for both training and competing. These carbohydrates get stored as muscle glycogen, needed to perform exercise (for faster use), and as liver glycogen, needed to maintain normal blood glucose level (for slower energy use).
The carbohydrates in sugary soda or sports drinks get stored as glycogen but provide little or no vitamins or minerals. The carbohydrates in wholesome fruits, vegetables, and grains also get stored as glycogen plus provide vitamins and minerals, which are the spark plugs that help the athlete’s “engine” to perform at its best.
The average 150 pound active man has about 1800 calories of carbohydrates stored in his liver, muscles, and blood, in the following proportions: muscle glycogen about 1400 calories; liver glycogen, 320 calories; blood glucose, 80 calories.
These carbohydrate stores determine how long an athlete can exercise, although with endurance exercise our bodies also burn fat for fuel, with training enabling us to burn more fat than less fit individuals. Depleted muscle glycogen results in “hitting the wall” and the associated painful muscles and difficulty moving. Depleted liver glycogen results in low blood sugar and causes the athlete to “bonk” or “crash”, feeling extremely fatigued, lightheaded, uncoordinated, and unable to concentrate. Proper daily and pre-exercise nutrition can significantly reduce the development of these problems.
Carbohydrates are important for all athletes regardless of the sport; both runners and weightlifters/body builders need carbohydrate as important fuel.
For adults the requirement for protein is 0.8-1.5 g/kilograms body weight per day (0.5-0.8 g/pound body weight for active adults; 0.8-1 g/lb. body wt. for the growing athlete). Approximately 5% of the energy cost of exercise is derived from protein. Excess protein does not build muscle, exercise does. To have adequate energy to perform the muscle building exercise, and recovery, the diet should be approximately 15 to 20% protein.
Endurance athletes need more protein per kilogram than bodybuilders/weightlifters; dieters need more protein than athletes eating their full complement of food; athletes rapidly building muscle have higher protein needs. Vegetarian athletes can obtain adequate protein for their needs, but their diets are still likely to be deficient in iron and zinc, 2 minerals found primarily in animal proteins, particularly in red meats. Iron is important for preventing anemia; zinc is important for healing.
Fats are also essential for a healthy diet, and besides supplying energy, also supply essential fatty acids and fat soluble vitamins. However, for both cardiovascular health and optimal sports performance, athletes should reduce their intake of fatty, greasy foods such as donuts, pastries, butter, mayonnaise, french fries, and ice cream, which tend to leave the muscles unfueled, and also may contribute to elevated blood cholesterol and associated heart disease. Dietary goals concerning fat, should provide low cholesterol, minimal saturated and trans fats, in the form of lean meats, and especially fish — fish are beneficial in lowering blood cholesterol and triglycerides. A healthy diet should consist of approximately 25% of these healthy fats.
Minerals and Vitamins
Some minerals important for muscle, nerve, and many bodily functions include: sodium, potassium, calcium, and trace amounts of iron, zinc, magnesium, chromium, and copper.
People at highest risk of suffering from iron deficiency anemia: female athletes (who lose iron through menstruation); athletes who eat no red meats; marathon runners (who may damage red blood cells through “foot strike hemolysis”); endurance athletes (who may lose a significant amount of iron through heavy sweat losses); and teenage athletes (who are growing quickly and may consume inadequate iron to meet their expanded requirements). Iron from a supplement may be poorly absorbed compared with that found in animal proteins. People who are deficient in iron may also be deficient in zinc because these 2 minerals tend to be found in similar foods.
Vitamins are important for many biological body functions, including muscles, brain and nerves, and other internal organs, but caution should be followed to not take too much vitamins — many authorities believe that vitamin supplementation is not necessary with a proper diet.
Water / Fluids
Fluids transport nutrients to and from the working muscles, dissipate heat (prevent heat exhaustion), and eliminate waste products. Dehydration, when occurring with muscle and/or red blood cell damage, can lead to acute kidney failure. However, excessive intake of water by marathon runners (along with inadequate minerals, mainly sodium and potassium, as well as inadequate calorie intake) has led to water intoxication, which can cause restlessness, weakness, nausea, vomiting, muscle twitching, convulsions, and even death. Drinking large quantities of water can delay gastric emptying, which can lead to bloating and reduced performance. Dehydration is much more common of a problem.
To maintain optimal hydration, athletes should follow these guidelines:
1. Prevent dehydration during training by replacing sweat losses during exercise: each pound of weight lost equals 2 cups (16 ounces) of sweat. Try to lose no more than 2% of your body weight during a workout (that is, 3 pounds or 3 cups of sweat for a 150 pound athlete). If you become 2% dehydrated, then your work capacity is reduced by 10 to 15%.
2. Before an event, drink 2 to 3 large glasses of fluid up to two hours before the start. The kidneys require about 90 minutes to process fluids, which allows time to empty the bladder prior to the event. Then 5 to 10 minutes before start time, drink another one or 2 cups of water or sports drink.
3. During hard exercise, or hot weather, ideally drink 8 to 10 ounces every 20 minutes; start drinking early in the event before you are thirsty, to prevent dehydration. 1 cup is 8 ounces, therefore drink 3 to 4 cups per hour, or every 5 to 6 miles if you run a 12 or 10 minute per mile pace, or at least 1 cup every 2 miles.
4. After exercise: the thirst mechanism inadequately indicates whether the body is optimally hydrated; monitoring urination is safer — if several hours passed before an athlete has urinated, or if urine color is dark, then he or she is still dehydrated.
For endurance athletes and those exercising for more than 90 minutes, a sports drink or diluted juice that contains 60 to 100 calories per 8 ounces is best during exercise.
Pre-Competition Meal (Mostly Carbohydrates)
3-4 hrs. before race time for a large meal to digest;
2-3 hrs. for a smaller meal;
1-2 hrs. for a blended or liquid meal;
less than 1 hr. for a light snack, as tolerated.
Eating During Exercise
Trained athletes can metabolize about 1 gram of carbohydrate per minute, at 4 cal./gram of carb. equals 240 cal./hr. of endurance exercise, or 60 cal. per 15 min. (about 8 oz., or 1 cup, of sports drink).
During intense exercise (>70% of aerobic capacity), the stomach gets only 20% of its normal blood flow; during moderate-intensity exercise, the blood flow is 60-70% of normal, so digestion may be fairly good (e.g. for recreational marathon and ultra-marathoners). Be sure to experiment with food and fluids during training to determine your tolerance and what works best for you.
Post-Competition / Recovery Eating
Muscles are most receptive to replacing muscle glycogen within the first 2 hours after a hard workout, therefore 200-400 calories of carbohydrate are recommended, then repeat another 2 hrs. later. Early intake of protein helps with the muscle repair process.
For estimating caloric needs for weight maintenance, multiply the desired weight by 12-15 cal./lb. for moderate activity; 15-20 cal./lb. for higher levels of activity.
For weight reduction, a gradual weight loss (1/2 -1 lb./wk. for women; 1-2 lbs. for men) offers greater long-term success. Each 3,500 calories lost = 1 lb. of weight lost; e.g. a combined decreased intake of 250 cal. with increase in exercise of 250 cal. per day, 7 days/wk.