Nutrition, training, & energy metabolism.

You tie on your shoes; you head out the door, you run. Simple. But, how fast you can run and how far you can run depends ultimately on what you feed your body--how it uses that food to produce energy, and how you utilize that energy with training. Your diet can help you to run your best if you understand the ways in which the body produces energy and the relationships between nutrition, metabolism, and optimal training. There is a recipe for success--you just need the right ingredients.

The Basics

Experts generally agree that a diet consisting of about 55% to 60% carbohydrates (mostly complex carbs, not simple sugars), no more than 30% fats (mostly unsaturated plant fats), and about 10% to 15% protein is consistent with both good health and optimal performance. The body converts the energy in carbohydrate, fat, and, to a very small extent, protein to chemical energy in the form of adenosine triphosphate (ATP). This is the body's form of energy currency necessary for absolutely everything it does. When the three-phosphate form (ATP) is converted to the two-phosphate form (ADP), the reaction powers all processes in the body. Since only small amounts of ATP are stored in muscle, the body must constantly replenish ATP. There are three processes, or energy systems, that do this job.

Why Power Lifters Pump Creatine and Marathon Runners Don't

The first energy system is ATP/phosphocreatine (ATP/PCr). In a single chemical reaction, the phosphate on creatine can be donated to ADP to regenerate one ATP molecule. This energy system is important in the first few seconds of vigorous exercise and is the dominant energy system for very high-intensity, very short duration (less than 30 seconds) activities such as power lifting and sprinting. Fondly called the Sprinters'Energy System, it doesn't use the fuels stored in the body like glucose and fatty acids.

The second energy system, called anaerobic glycolysis, is also known as the Lactic Acid Energy System. This system uses glycogen to produce ATP. Glycogen is the stored form of carbohydrates found in muscle and the liver. Glycogen consists of glucose molecules strung together in a highly branched arrangement, like clumps of seaweed. In a series of chemical reactions in the cell, a single glucose unit from glycogen is partially broken down, resulting in a net yield of three ATP molecules and two lactic acid molecules.

This energy system is also important in the first few seconds of exercise and is the dominant energy system for high-intensity, slightly longer activities (such as a 400-meter run duration from 30 seconds to two minutes). Both the creatine reactions and anaerobic glycolysis energy systems are anaerobic energy systems, meaning that oxygen is not required for these energy systems to operate.

The third system, known as the Oxygen Energy System breaks down glycogen and fats in the presence of oxygen to regenerate ATP. The aerobic system generates lots of ATP. When oxygen is delivered to the mitochondria (the cell's powerhouse) of exercising muscles in sufficient quantity, one glucose unit from glycogen undergoes complete breakdown to regenerate as many as 39 ATP molecules. Fatty acids are also used in the presence of oxygen to produce even larger amounts of ATP. Fatty acids are stored in fat cells and in muscle, and are a rich source of potential energy ATP generation, but only in the presence of oxygen.

Why Should You Care About VO2max, Tempo Runs, or Lactate Threshold?

Aerobic fitness is best measured by maximal oxygen consumption ([VO.sub.2]max), which tests the integrated ability of the pulmonary and cardiovascular systems to take in and transport oxygen and the ability of exercising muscle to use the delivered oxygen. When exercise begins or the intensity of exercise is increased, more ATP is needed by the muscles. Even if the exercise is at a comfortable sub-maximal intensity, there is a lag time of approximately one to two minutes between the need for oxygen and the ability of the lungs, heart, blood, and vessels to deliver it. In other words, oxygen demand temporarily exceeds oxygen supply. This phenomenon is known as oxygen deficit, during which both the ATP/PCr and anaerobic glycolysis energy systems contribute ATP.

If the intensity of exercise continues to increase, a point will inevitably be reached where greater reliance is placed on anaerobic glycolysis for ATP resynthesis in order for you to keep running. This results in an increase in levels of lactic acid in the blood, a phenomenon known as the lactate threshold. If there is a further increase in exercise intensity, the lactic acid levels will continue to increase exponentially. Your body will respond by huffing and puffing gallantly to reduce acidity--you are blowing off the carbon dioxide produced by buffering the acidity.

What Does All This Biochemistry Mean to Me?

First, your diet must include the correct mixture of carbohydrates, fats, and protein for fuel. Vitamins and minerals serve to facilitate the chemical reactions that are involved in ATP formation. Water, of course, is the solvent in which all these reactions occur and is important for thermoregulation (maintaining your care temperature). Base mileage, including long runs, trains the body to effectively consume oxygen, and to make better use of fat so that glycogen is conserved.

Tempo running at or slightly above race pace not only helps improve your aerobic response to exercise, but also trains the anaerobic response because such a training pace is near or above the lactate threshold. in addition, tempo running mimics the pattern of muscle motor unit recruitment during actual competition. Both tempo running and anaerobic intervals (in which excess lactic acid accumulates in the blood, for example, eight, 400 meters, with one- or two-minute rest intervals) train the athlete to better tolerate the acidity that is associated with high intensity, sustained exercise. Tempos and interval training usually result in a lactate threshold that is at a higher percentage of the athlete's [VO.sub.2]max, a classic marker of improved performance.

These principles are what's behind good training. You need a "dash" of proper nutrition and a "dose" of intelligent training in your recipe for staying healthy, keeping fit, and running personal bests.

If this energy primer tweaks your technical interests, Exercise Physiology, Energy Nutrition, and Human Performance, by McCardle, Katch and Katch, 1996, 4th edition, Lippincott, Williams, and Wilkins, Baltimore, MD, will give you more ideas. (J. David Branch, Ph.D., is Assistant Professor of Exercise Science in the Department of Exercise Science, Physical Education, and Recreation at Old Dominion University in Norfolk, Virginia.)

RELATED ARTICLE: Who needs a nutritionist? Maybe you!

What we eat helps prepare us for peak performance. Food choices also promote ongoing health and prevent disease long after the race is run. Registered dietitians have the skills and knowledge to translate nutrition science into practiced solutions for your food choice needs. Their expertise includes food composition, eating patterns and your feelings about them, meal planning for you and your family, tips for eating on the run wherever you are, and how supplements interact with the foods you eat.

The title nutritionist doesn't require particular credentials and there are many self-proclaimed experts you should avoid. Qualified nutritionists include university-trained professionals in nutrition, education, food science, and exercise physiology. The professional credential Registered Dietitian (RD) identifies a qualified nutrition professional who has completed a rigorous academic program in nutrition and maintains this credential through continuing education. If you are a serious, competitive athlete, look for a registered dietitian who specializes in sports nutrition--a member of the Sports, Cardiovascular and Wellness Nutritionists (SCAN) practice group of The American Dietetic Association or a fellow of the American College of Sports Medicine (FACSM).

Registered dietitians will custom design an individualized and flexible nutrition plan that meets your lifestyle and activity requirements. Call and interview several potential registered dietitians in your area who have the specialized expertise you might need. Ask what to expect at the first consultation and what you will go away with. You want a professional relationship that is supportive and non-judgmental. Accept nothing less.

Nutrition counseling can be a major boon to your training--an investment in your general health and your running performance. You probably think nothing of putting $100 an your feet--the same investment in nutrition counseling can serve you well into the future. Nutrition consultation fees vary according to geographic region and specialty. Fees can range from $100 to $200 for an initial consultation. Expect to see a benefit from your investment by learning how to make the proper food choices to maximize health and power your training. You can find a registered dietitian in your area through ADA's Web site at www.eatright.org or through American Running's Network at www.americanrunning.org.

(Mary Jo Feeney, RD, is a Fellow of the American Dietetic Association and a member of the Running & FitNews Editorial Board. She can be reached at [e-mail])

If you answer YES to any of these questions, you could BENEFIT from a consultation with a NUTRITIONIST.

* Are you a serious runner looking for an edge?

* Do you exclude major food groups from your food choices for any reason (personal, ethical, environmental)?

* Are you a women considering pregnancy?

* Do you have a family history of chronic disease such as coronary heart disease or diabetes?

* Have you been diagnosed with a health condition that limits your food choices?

* Do you find it difficult to maintain a healthy weight while being physically active?

* Are you concerned that you may have an eating disorder--fear of eating, fear of fat, or do you know or think you are ancresic or bulimic?

* Does your lifestyle in general make in difficult for you to make healthy food choices?

* Have you tried to maintain a healthy weight by adjusting your diet and not been successful?