Due to the fact that one of the two ways to increase the strength of a muscle contraction is to increase the frequency at which the motor units fire in order to create a summed effect, it is expected that the shorter the time interval between consecutive stimuli, the greater the force of contraction. If there is a greater amount of time between the stimuli, the muscle would be able to relax before the next stimulus is fired. However, as that time decreases, the individual twitches begin to overlap and produce a stronger contraction. If a skeletal muscle is stimulated before it is able to fully relax, the sarcoplasmic reticulum will continue to release more calcium ions, more cross-bridges will form, and the muscle will contract again under
