Adenosine Triphosphate (ATP) – The Necessary Fuel – Part 1

The human body has always fascinated me and as I have sat in the Anatomy and Physiology class the last few months, I have had several ‘aha’ moments. The co-dependence of the different systems of the body to regulate and maintain the body’s proper functioning that extends to the cellular level of the body has completely amazed me.  It is hence not hard to conclude that no man-made system can be compared to the human body in its inherent complexity and perfection.

When we exercise for instance, there are physiological changes that occur in the heart, the blood vessels, the respiratory system and the muscle tissue all at the same time.

For the purpose of this paper however, I will like to focus on how the body responds to exercise at the muscle tissue level and specifically discuss how we get energy.

When we exercise, the muscles act something like electric motors that uses electricity to supply its energy. Our muscles are biochemical motors, and they use a chemical called adenosine triphosphate (ATP) for their energy source (Freudenrich, Ph.D., 2010). The primary function of ATP is the transfer of energy from one location to another rather than the long-term storage of energy (Martini, 2008). When the muscles are in a relaxed state, they use only a modest amount of ATP and as the muscle activity increases, the muscles begin contracting and extending and the use of ATP increases at a rapid pace.  The ATP present inside the muscle fibers is enough for power contractions that last only a few seconds and as the duration of physical exercise increases, additional ATP must be synthesized. This contraction and extension of the muscles fibers that facilitates ATP production is known as the sliding filament mechanism. Here the thin filaments at both ends of the sarcomere are pulled to center by the myosin head activity and the Z discs come closer together that leads to shortening of the sacromere (Jenkins et all, 2007). The stimulation of the fiber prompts the formation of tiny cross-bridges that extend from the myosin filament and attach to active sites on the actin filament.  The release of calcium ions within the muscle fiber exposes these active sites, facilitating the attachment of the two kinds of fiber to one another.  Each cross-bridge exerts a pull on the actin filament, causing the actin and myosin filaments to slide past one another.  Under the influence of chemical substances released in the binding process, each cross-bridge is then disconnected from its binding site on the actin filament and moves to a neighboring site.  Since the process happens simultaneously in all of the cells of muscle, the entire muscle contracts. The ATP fuels actin and myosin interaction and this leads to muscle contraction (Feinberg, 1991).

During the process of “burning” ATP, our muscles need three things:

• They need oxygen, because chemical reactions require ATP and oxygen is consumed to produce ATP.
• They need to eliminate metabolic wastes (carbon dioxide, lactic acid) that the chemical reactions generate.
• They need to get rid of heat. Just like an electric motor, a working muscle generates heat that it needs to get rid of. (Freudenrich, Ph.D., 2010)