Fitness gurus and blogs claiming these products are essential for peak performance, fat loss, and rapid muscle growth, along with complicated scientific-sounding names and labels, can trick you into thinking you can't exercise effectively without them. But do these supplements live up to the hype and are they necessary—or in some cases, safe? Like other nutritional supplements in the US, the Food and Drug Administration (FDA) does not review exercise supplements for safety or effectiveness before they are sold to consumers. It's a good idea to research their effects and ingredients and consult your doctor before adding them to your fitness routine.
What are the changes in the body during physical activity?
When we exercise, our body uses three main sources of fuel: carbohydrates, fats and proteins. Carbohydrates, stored in the liver and skeletal muscles in the form of glycogen, provide the most efficient source of energy during exercise. Glycogen is easily metabolized into glucose, which provides immediate energy to power the brain, nervous system, and muscles during exercise. The body's glycogen stores can provide enough fuel for 90-120 minutes of intense activity. Depletion of the body's glycogen stores creates a "hitting the wall" feeling during exercise. When glycogen stores are depleted, the body begins to break down fat to burn for fuel, especially during low- to moderate-intensity activity. In the final stages of prolonged exercise, when glycogen stores are at their lowest, the body begins to break down skeletal muscle protein to produce glucose. Physical activity can also cause muscle growth, also known as hypertrophy. Weight lifting and other resistance exercises are often used to increase skeletal muscle mass, but cardiovascular exercises such as running can also stimulate muscle growth. Physical activity causes damage to the structure of muscle fibers, especially when the muscles are stressed by many repetitions of heavy weight. The body's regenerative response involves combining broken muscle fibers to form new muscle protein fibers, which in turn increases muscle size. Several factors affect how quickly muscles grow during exercise, including the amount of weight lifted and the number of repetitions.
