Nutrition and Energy Sources for Athletic Performance

Introduction: Nutrition and Athletic Performance

One of the most important parts of an athlete's training regimen is nutrition, because of its central role in human performance. Athletes need to focus on nutrition because the failure to ingest adequate calories can contribute to a lack of vital macro and micronutrients. Nutrition is a crucial element in any athlete's training regimen given the influence of food on physical function. Throughout history, certain foods have been regarded as essential in preparation for strenuous physical activity or exercise. As part of their nutritional focus, athletes need to consider various factors that contribute to nutrition in relation to physical activity and exercise. Some of these important considerations include types of food and food sources that help in preparation for physical activity, health, fitness, and human performance.

Glycogen, Energy Expenditure, and Exercise

Glycogen can be simply defined as the storage form of carbohydrates and glucose in human beings and animals (Millan par. 8). In addition to being a large, multi-branched polymer of glucose, glycogen is stored in the form of glucose. This stored glucose is accumulated in response to insulin and broken down into glucose in response to glucagon. Generally, glycogen is largely stored in the muscles and liver and provides the body with a readily available energy source when blood glucose levels fall.

Glycogen is important in exercise because it is a preferred form of stored energy and serves as an energy source for the brain. Its significance during exercise lies in the ability of glucose to provide energy for cells when oxygen is absent — such as during anaerobic exercise. Therefore, glycogen provides a readily available source of energy for the body that is particularly useful during exercise.

While physical activity is the primary factor driving energy expenditure, certain activities represent high energy expenditure, including running, intense cycling, and weight-bearing activities. These activities expend more energy because they engage large muscle groups in a continuous, systematic way.

Energy utilized during exercise is supplied primarily from two major sources: fats and carbohydrates. Fat supplies energy stored throughout the body, while carbohydrates supply energy in the form of glycogen stored in the muscles. During exercise, an individual uses both energy sources: at high intensity, carbohydrate is the dominant energy source, while fat dominates at low intensity. Because the quantity of carbohydrate that can be stored in muscles is limited, high-intensity work cannot be maintained for long periods, whereas low-intensity work can be sustained for longer due to the large amount of fat stored in the body. Factors that influence the availability and use of energy sources during exercise include the duration of exercise, the intensity of exercise, initial levels of muscle glycogen, the level of exercise training, and carbohydrate intake during exercise.

Carbohydrates: Loading, Performance, and Prolonged Events

Carbohydrates are one of the most important sources of energy, especially for high-intensity work. Food sources of carbohydrates include vegetables, fruits, brown rice, oatmeal, and whole wheat products. Foods containing carbohydrates have been identified as having the most significant effect on exercise performance. Carbohydrates enhance sports performance with respect to event length by providing the energy necessary for ATP synthesis, which is critical because high exercise intensities associated with sports increase demand for ATP production. An example of a 30-gram carbohydrate snack includes a fruit and grain bar, one English muffin, a banana, animal crackers, 20 baked tortilla chips, one cup of sugar-free pudding, or six graham cracker squares.

Carbohydrate loading is a strategy used by some athletes to maximize energy or glycogen storage in the muscles. Athletes who benefit from carbohydrate loading are those involved in endurance sports such as marathon running. Beyond marathoners, other athletes who benefit include triathlon participants and football players. Conversely, athletes not involved in endurance sports or exercises do not benefit from carbohydrate loading.

The process of carbohydrate loading uses a regimen developed through research in the 1980s. This regimen, which removes the earlier depletion phase, entails increased carbohydrate intake and reduced training for at least three days before an event ("The Role of Carbohydrates in Exercise" par. 8). In some cases, carbohydrate loading involves following a normal diet combined with light training until the eve of the event.

Although carbohydrate and fat are both basic energy sources, carbohydrate acts as the body's principal source. Protein provides a minimal amount of energy under ordinary conditions. Prolonged athletic events typically involve low-intensity work that the body can sustain, rather than high-intensity efforts. The main energy source for prolonged athletic events is carbohydrate, which, though primarily associated with high-intensity exercise, is also utilized at low exercise intensities. Carbohydrate serves as the main energy source for prolonged events because fat cannot provide the required energy for ATP synthesis on its own. Trained athletes utilize carbohydrate fuel more effectively because their diets incorporate adequate carbohydrate intake, and their training regimens emphasize not only varied exercise but also proper dietary planning for carbohydrate consumption.

Carnitine plays an important role in fatty acid metabolism by transferring long-chain fatty acids into mitochondria for improved beta-oxidation (Heinonen, p. 109). In recent years, supplementary carnitine has been widely used to enhance fat metabolism and physical performance, despite the absence of conclusive scientific support. This means there is no strong scientific evidence for athletes or healthy individuals to use carnitine supplements to enhance exercise performance. Furthermore, athletes do not have an elevated need for carnitine, as they are not at risk of carnitine deficiency. While it is possible for individuals to enhance muscle carnitine content through diet, fat metabolism and physical performance are largely dependent on exercise intensity, which drives improved energy use and performance. Despite the lack of definitive scientific evidence, some still use carnitine supplements in the expectation of enhancing fat metabolism and performance.