When the body requires energy, it can utilize different fuel sources, including fats and carbohydrates. Muscles rely on stored energy during exercise or physical activity to perform work. Here's a simplified explanation of how muscles use fat for fuel:
Energy availability: When the body needs energy, it initially uses readily available sources like glucose (carbohydrates) circulating in the bloodstream. Glucose provides quick energy but is limited in supply.
Glycogen stores: As the body's demand for energy continues, it taps into glycogen stores. Glycogen is a complex carbohydrate stored in the liver and muscles. It can be quickly broken down into glucose and used as an energy source.
Fat mobilization: If exercise or activity persists beyond the immediate availability of glucose and glycogen, the body starts mobilizing stored fat as an energy source. Fat is stored in adipose tissue throughout the body.
Lipolysis: Breaking down stored fat into fatty acids and glycerol is called lipolysis. It occurs in specialized cells called adipocytes. Hormones like epinephrine and norepinephrine, released during exercise, stimulate lipolysis.
Fatty acid oxidation: Fatty acids released from adipose tissue travel through the bloodstream and reach the muscles. Inside the muscle cells, fatty acids undergo a series of chemical reactions called beta-oxidation. This process breaks down the fatty acids into acetyl-CoA molecules.
Acetyl-CoA metabolism: Acetyl-CoA enters the Krebs cycle (also known as the citric acid cycle or TCA cycle) in the mitochondria of muscle cells. Through a series of reactions, acetyl-CoA is further broken down, generating energy-rich molecules like ATP (adenosine triphosphate).
Energy production: The ATP generated through the breakdown of fatty acids provides energy for muscle contraction and other cellular processes required during exercise or physical activity.
It's important to note that fat is an abundant energy source, but it takes longer to mobilize and metabolize than glucose. The intensity and duration of exercise and individual factors such as fitness level and metabolic rate influence the proportion of energy derived from fat. In low-intensity activities or endurance exercises, the body tends to rely more on fat as a fuel source. However, during high-intensity exercises, carbohydrates become the primary energy source.
