Muscle Is Fueled Primarily by Carbohydrates + Fat
What fuels muscle activity?
Muscle contraction is fueled by ATP (adenosine triphosphate), which is generated by both anaerobic and aerobic energy metabolism. Because ATP is found in low concentrations in all cells of the body, these ATP-generating mechanisms must be increased with the onset of activity in an attempt to meet ATP demands of working muscle cells. This means that muscle cells need to stoke up those chemical reaction pathways that break down carbohydrate and fat for ATP generation as the low level of ATP at the onset of exercise is quickly exhausted (seconds). Muscle cells have a little stored carbohydrate (glycogen) and fat and also receive glucose and fatty acids from the blood. So increased blood delivery to the exercising muscle delivers not only needed O2 but also fuel. Stored muscle carbohydrate is a faster energy source than fat as well as blood sources. Meanwhile it will be the intensity and duration of exercise along will that will be the primarily the relative contribution of the different potential sources in general.
What is creatine?
Another power source for working muscle is creatine phosphate. Creatine is a substance found mostly in skeletal muscle cells, but it is also found in heart muscle cells and brain. When ATP is abundant in these cells, such as while muscle is not active (at rest), phosphate is transferred to creatine. This forms creatine phosphate, which is a rapid ATP-regenerating source. When ATP is used to power muscle contractions, the phosphate of creatine phosphate can be transferred to ADP to regenerate ATP. This involves only one chemical reaction and can happen very rapidly.
How does creatine power skeletal muscle efforts during exercise?
This regeneration of ATP from creatine phosphate is especially important for quick burst activities such as sprinting and weight training. However, this system is extremely limited and will last only a few seconds. Yet this function helps muscle cells bridge the gap between the rapid depletion of ATP at the onset of exercise and the point when a muscle cell’s other ATP-generating operations are appropriately stoked up. Then, when the muscle cell is resting (in between sets or between sprints) creatine phosphate is regenerated to prepare for the next exercise effort.