1 Chemically, ATP is an adenine nucleotide bound to three phosphates. 2  There is a lot of energy stored in the bond between the second and third phosphate groups that can be used to fuel chemical reactions. 3  When a cell needs energy, it breaks this bond to form adenosine diphosphate (ADP) and a free phosphate molecule.
calf muscle pump. calf muscle pump. an action of the calf (soleus) muscles in which the muscles contract and squeeze the popliteal and tibial veins, forcing the blood in those veins to move upward toward the heart. Also called soleus pump.
These chemical reactions produce adenosine triphosphate (ATP) molecules that are used to power the movement of the myosin heads. The term muscle is derived from the Latin musculus meaning little mouse perhaps because of the shape of certain muscles or because contracting muscles look like mice moving under the skin.