How is energy stored and released during muscle movement?

Energy is stored in muscles as ATP and released during muscle contraction to facilitate movement.

Muscle movement is a complex process that involves the conversion of chemical energy into mechanical energy. This process is facilitated by a molecule known as adenosine triphosphate (ATP). ATP is often referred to as the 'energy currency' of the cell because it stores the energy we need to do just about everything.

In resting muscles, ATP is produced by aerobic respiration in the mitochondria and stored for future use. During muscle contraction, the stored ATP is broken down into adenosine diphosphate (ADP) and inorganic phosphate (Pi), a process which releases energy. This energy is used to power the sliding filament theory of muscle contraction, where the protein filaments actin and myosin slide past each other to shorten the muscle fibres.

The breakdown of ATP is catalysed by an enzyme called ATPase, which is found on the head of the myosin filament. When ATP is hydrolysed, the myosin head is energised and attaches to the actin filament, forming a cross-bridge. The release of energy causes the myosin head to change shape and pull the actin filament towards the centre of the sarcomere, causing the muscle to contract.

Once the energy has been used, the ADP and Pi are released, and the myosin head detaches from the actin filament. The ADP and Pi are then recombined to form ATP in a process called oxidative phosphorylation, which occurs in the mitochondria. This ATP is then available to be used again in the muscle contraction process.

In summary, energy is stored in the muscles as ATP and released during muscle contraction to facilitate movement. The energy from ATP is used to power the sliding filament theory of muscle contraction, and the ADP and Pi produced are then recombined to form ATP, ready for the next contraction. This cycle of energy storage and release is essential for all muscle movement.