How Does Increasing The Stimulus Amplitude Increase The Contraction Force

Increasing the stimulus amplitude will increase the contraction force. Due to two conditions being satisfied: (1) the strength of the contraction force is changed through varying the number of muscle cells utilized for the contraction and/or varying the frequency of the stimulus, and (2) there is a distribution of the stimulus amplitude necessary to cause an action potential in the muscle cells, increasing the stimulus amplitude makes it likely that a potentially larger number of muscle cells will reach the threshold necessary to contract.
Increasing the stretch of the muscle will cause a decrease in the contraction force. This is because the stretching may reduce the overlap of the actin and myosin filaments and thus result in less potential