Biological effects of aerobic exercise: Fat oxidation mobilization mechanisms and four basic principles for choosing fat loss programs

The mechanical energy used for work during human movement is converted from the body's bioenergy. There are three pathways for bioenergy production: the phosphagen system, the lactic acid system, and the aerobic oxidation system. Fat breakdown in the body can only occur through the aerobic oxidation pathway; that is, only aerobic exercise can utilize body fat for energy. Therefore, only aerobic exercise can maximize weight loss.

Aerobic exercise is characterized by low intensity and long duration. Most long-duration, full-body exercises are aerobic. When the intensity exceeds the anaerobic threshold, lactic acid begins to be produced in large quantities. Lactic acid lowers the pH value inside muscle cells, thereby inhibiting the activity of enzymes in the fat oxidation system. Lactic acid production is not allowed during exercise for weight loss.

"Pure" aerobic exercise involves exerting 20% ​​to 40% of your heart rate reserve for at least 30 minutes. Exercise intensity is key to effectiveness; higher intensity does not necessarily mean better results. Protein is generally not a primary energy source. Carbohydrates and fats are the main energy-providing substances. However, the energy-producing ratio of these two substances varies at different intensities.

Fat is burned most efficiently at low to moderate intensity. Too low an intensity results in a small absolute amount of fat burned, while too high an intensity also results in minimal fat loss; both are ineffective. For weight loss through exercise, it's best to maximize the proportion of energy derived from fat. Effective fat-burning exercise requires consistent duration, a crucial factor being that it must be sustained for a certain period.

Just as cars need gasoline to run, humans need nutrients to "burn" during exercise. Carbohydrates are a direct energy source, while fats are energy storage substances. Carbohydrate oxidation is a simple and rapid process. Fat oxidation involves a complex enzyme system and many steps. Skeletal muscle energy supply follows a "proximity principle," primarily utilizing the oxidation and breakdown of muscle glycogen.

Fatty acid oxidation and breakdown occurs very slowly. Recent research shows that it generally takes 20-30 minutes for mobilization. There are also gender differences, with women taking longer to mobilize. In most cases, fat burning only begins after more than 30 minutes of continuous exercise. This is why exercise lasting less than 20 minutes has little effect.

During high-intensity exercise, the body primarily uses the phosphagen system and anaerobic glycolysis for energy. The metabolic product of anaerobic glycolysis of muscle glycogen is lactic acid, which inhibits fat oxidation and breakdown. During sustained high-intensity exercise, glucose becomes the main energy source. This significant glucose depletion leads to a pronounced feeling of hunger. High-intensity exercise often results in a phenomenon where the more you exercise, the more likely you are to gain weight.

During moderate-intensity sustained exercise, the proportion of energy supplied by fat oxidation begins to increase after 20-30 minutes. After about 3 hours of exercise, almost all energy is provided by fat. For weight loss, exercise should be low to moderate intensity for extended periods. Later in the exercise program, to increase skeletal muscle mass, it is necessary to supplement with higher intensity exercises to boost the body's metabolic rate.

The basic principles for choosing a weight loss exercise program are: full-body exercise; sustainable long-duration aerobic exercise; exercise that you enjoy; and exercise that is safe. Full-body aerobic exercise provides energy through fat breakdown. However, the downside is that it can easily become monotonous, so choosing something you like and are interested in will help you stick to it long-term.

Safety must be emphasized. Because obese patients are overweight and have limited mobility, safety requirements are even more stringent. Avoid activities that easily cause joint damage or are difficult to control in intensity. Exercises that violate these principles, such as sprinting, skipping rope, or rapid push-ups, not only easily cause injury but also are unlikely to yield good results.