unfused tetanus

Unfused tetanus occurs when a muscle receives repeated electrical stimuli at a rate that causes tension to rise in waves, rather than a constant, sustained contraction. This happens because each stimulus triggers a muscle contraction, but there's a brief refractory period after each action potential during which the muscle cannot respond to further stimulation. If the stimuli are spaced too far apart (more than 300 milliseconds in a frog sartorius muscle at 0°C), the muscle begins to relax between contractions, resulting in an unfused tetanus. This is a form of temporal summation, where successive stimuli add up to generate a response. The maximum tension achieved during unfused tetanus is typically higher than that of a single twitch but lower than that of a fused tetanus.12