The motion of contracted muscles happens when myosin head binds with actin and pulls it inward. This type of motion requires the use of energy that is provided by ATP. On the other hand, in order for the muscle to relax, it also needs the energy produced by ATP to break the break the bonds between the two. Without ATP, the muscles will remain contracted until ATP produces the energy that is needed to break the bonds.
ATP or adenosine triphosphate is considered the “molecular currency” of the energy that is transferred between our cells. This nucleotide provides the power that our body needs to perform different activities such as protein construction, muscle contraction, cell communication, and substrates transportation.