Time is required to take up slack and stretch the noncontractile components, and while this is happening, the internal tension is already declining. So, in brief twitch contractions, the external tension is always less than the internal tension. However, when a muscle is stimulated rapidly, contractions are summed, becoming stronger and move vigorous and ultimately producing tetanus. During tetanic contractions more time is available to stretch the noncontractile components, and external tension approaches, the internal tension. So, the more rapidly a muscle is stimulated, the greater the force it exerts.