The sliding filament theory is the term for the process that describes how a thin filament slides across a thick filament to generate a muscle contraction. A series of steps take place so that the muscle can generate the tension required to contract.
A nerve impulse triggers the release of a chemical that causes calcium to be released from the endoplasmic reticulum. The calcium then binds with troponin. This molecule is now able to able to connect to actin. Energy from adenosine triphosphate, or ATP, permits the tropinin/calcium/actin molecule to pull the actin filaments so that the thin filament glides across the thick filament and causes the muscle to contract. The length of the contraction depends on how much ATP and calcium are present.