What is the function of mitochondria in muscle fibers?

During strenuous exercise, the rate of energy use in skeletal muscles can increase by more than 100-fold almost instantly. To meet this energy demand, muscle cells contain mitochondria. These organelles, commonly referred to as the cell's “power plants,” convert nutrients into the molecule ATP, which stores energy.

enzyme speed up the reactions

the electromagnetic energy from the sun arrives in the form of visible and invisible light.