Final answer:
The summation of force occurs in skeletal muscle because repeated stimuli are required to elevate calcium to peak levels. Wave summation, caused by high-frequency stimuli, leads to stronger muscle contractions. The release of more calcium ions during wave summation allows for greater muscle contraction and tension.
Step-by-step explanation:
Summation of force occurs in skeletal muscle because repeated stimuli are required to elevate calcium to peak levels. When a motor neuron fires action potentials at a high frequency, wave summation occurs, resulting in stronger muscle contractions.
The second stimulus triggers the release of more calcium ions, which activate additional sarcomeres while the muscle is still contracting from the first stimulus. This leads to greater muscle contraction and tension.