Energy and Metabolism
Energy releasing processes, ones that "generate" energy, are termed exergonic reactions. Reactions that require energy to initiate the reaction are known as endergonic reactions. All natural processes tend to proceed in such a direction that the disorder or randomness of the universe increases. The fact that energy expenditure is related to body weight and even more closely to fat-free mass is well recognized. Evidence also supports the independent contribution of fat mass to the variance in energy expenditure. Therefore, it is not surprising that changes in body weight and composition induce proportional changes in energy expenditure. Despite this, it is now becoming apparent that factors other than body composition can influence the changes in energy expenditure that occur in response to weight loss.
Skeletal muscle is important in the regulation of energy expenditure and constitutes an important site for the utilization of both carbohydrates and lipids. Because the synthesis and re-synthesis of ATP within skeletal muscle is the result of five energy-generating pathways, and because there are rate-limiting enzymes in each of these pathways, it could be speculated that these enzymes influence energy expenditure. Doucet et al. hypothesized that inter-individual differences in the decrease in key enzymes involved in energy expenditure might be partly responsible for the changes in energy metabolism that occur in response to weight loss. This current study performed by some Canadian researchers investigated the relation between skeletal muscle enzymes and 24-hour energy metabolism in obese persons before and after weight loss.
Potential energy is stored energy, whereas kinetic energy is energy of motion: laws of thermodynamics govern movement of energy; according to the first law of thermodynamics, energy cannot be created or destroyed, although it can be transferred or changed from one form to another; total energy in universe has remained constant, but it is continuously becoming more diffuse through the universe.
The second law of thermodynamics states that when energy is converted from one form to another, some usable energy, some is degraded into a less usable form, i.e. heat.
It should be mentioned that entropy is a measure of disorder or randomness, it is organized, usable energy has low entropy, whereas disorganized entropy such as heat has high entropy. All energy conversions have efficiencies