Physical activity metabolizes stored fat, which reduces the size of the fat stores, while increasing lean body mass. Both of these effects help the body to achieve and/or maintain a normal metabolic rate. Weight loss cannot be predicted or even guaranteed as a result of physical activity, but the metabolic effects of physical activity are important in preventing further fat gain and, in most people, will promote at least some fat losses.
In the first minutes of moderate exercise, before aerobic metabolism can fully power up, carbohydrates, creatine phosphate, and stored ATP (Adenosine triphpspahate) are used for fuel. After a few minutes, lipid oxidation progressively increases, gradually surpassing use of carbohydrate as an aerobic exercise fuel, as fatty acids are released from adipocytes. Lipids make their greatest contribution to metabolism during exercise at about 65% of maximal oxygen uptake.
People who engage in regular activity and improve their physical fitness use more lipids for fuel and begin burning fat earlier during exercise.
Lipids are not just used as fuel during exercise, they also make a substantial contribution to energy expenditure after exercise through excess postexercise oxygen
What are Lipids?
Lipids are fat like substances found in the blood stream or stored in the body. Lipids are derived from two main sources, exogenously from food and endogenously made in the liver. Lipids are essential for many functions such as building cell membranes, brain functioning and to synthesize hormones. If lipids are excessive these can stick to the blood vessel walls and form a buildup called plague, which can block the blood flow to the heart or brain and cause heart attack or stroke.
The two types of lipids are:
LDL or the bad cholesterol transports cholesterol to tissues and arteries where the cholesterol can create blockages and hence is bad.
HDL or the good cholesterol. This prevents the build up of cholesterol in the blood vessels; higher the HDL the better
Physical activity is essential for weight management because it burns fat and increases muscle mass- two conditions that are metabolically favorable for weight loss, weight maintenance, or prevention of weight regain. The effects of exercise on appetite are variable, with some eating more and others not. But even among those individuals who partially compensate for increased physical activity by eating more, if energy out is greater than energy in, weight loss can occur.