What is the effect of increasing the frequency of electrical stimulation on muscle contraction?

Increasing the frequency of electrical stimulation typically leads to a stronger muscle contraction, a phenomenon often referred to as summation or tetanization. When stimulation occurs at a low frequency, individual muscle twitches are observed, and there is time for the muscle to relax between contractions. However, as the frequency increases, the muscle does not have adequate time to fully relax, resulting in a more sustained and forceful contraction. This build-up of tension occurs because the successive stimuli lead to increased calcium ion concentration in the muscle fibers, which engages more of the contractile elements within the muscle.

This effect is utilized in various therapeutic and training applications, where higher frequencies can be employed to maximize muscle engagement and strength. The physiological basis for this response lies in the mechanics of muscle fiber activation, where more frequent signals reinforce the contractile activity, fostering improved muscle performance.