For the sliding filament theory to take place the following needs to occur:
1. Calcium is released which allows the myosin head to bind with the actin.
2. The actin and myosin bind causing a cross-bridge.
3. The myosin heads pull on the actin causing the sarcomere to shorten and the muscle to contract.
4. When the muscle lengthens they return to the starting position ready to contract again.