Regardless of your fitness program and goals, nutrition plays an integral role in realizing results. Fueling up before your workout and replenishing nutrients after your sessions are key strategies for getting the most bang for your bite. Understanding how your body uses fuel during exercise will help you choose foods for peak performance.
Energy Essentials
Adenosine Triphosphate, or ATP, is the energy compound that works at the cellular level to make your muscles contract. Your muscle cells only store enough ATP to last a second or two before it must be re-manufactured. During activities of high intensity and short duration, your muscles contract anaerobically, or without oxygen. For sustained activities lasting more than two minutes, you need oxygen to continue to make ATP, and your muscles switch to aerobic fuels to keep contracting. Initially you draw on stores of creatine phosphate in the muscle cell, which is good for only 10 seconds or so of energy. After that, you must draw on glycogen, the storage form of glucose in your liver and muscles and on fat stored in your adipose tissue.
Carbohydrates As Fuel
Carbohydrate foods come from plants, and are ultimately broken down by your digestive system to glucose. Some of the glucose is stored as glycogen in the muscles and liver, some remains circulating in your bloodstream, and excess amounts are converted to body fat. Once you deplete creatine phosphate in your muscles, you draw on glucose and continue to make ATP anaerobically for about two minutes. Meanwhile, your heart and respiratory system are working hard to get oxygen to your cells so you can keep going. Once oxygen is present, you continue to use glucose aerobically as your primary fuel until glycogen stores become depleted, a duration of about 20 minutes.
Fats As Fuel
When glycogen stores get low, as long as the supply of oxygen can meet the demands of your muscle cells, you begin to tap into your adipose tissue stores to recruit body fat for fuel. Fat is strictly an oxidative, or aerobic fuel best suited to long duration rhythmic activities like walking, lap swimming, cycling or other aerobic exercise. While you need to eat some healthy fats for metabolic tasks like hormone production, most people do not need to consume extra fat to fuel their workouts, since most of us have ample stores available.
Protein: Fuel of Last Resort
Protein plays an important role in building muscle and connective tissue, but carbohydrates are your body's preferred fuel source. Inadequate carbohydrate consumption coupled with intense exercise can force you to use protein for energy by drawing amino acids from muscle tissue and converting them to glucose. Using protein for fuel wastes muscle tissue and may negatively impact physical performance. To rebuild and maintain lean muscle mass, athletic individuals should consume between 0.5 to 0.75 grams of protein per pound of body weight daily.
References
- Sports Fitness Advisor: Energy Systems in Sport and Exercise
- Peak Performance: Aerobic and Anaerobic Energy Systems
- Sports Medicine and Exercise Science Guide: Bioenergetics: How Humans Get the Energy to Move
- American College of Sports Medicine Fit Society Page: Nutrition: Who Needs It? If You're an Athlete, You Do!: Jane LeBlond, MS and Katherine Beals, PhD, Winter, 2007
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