If the stimulus frequency is so high that the relaxation phase disappears completely, contractions become continuous in a process called complete tetanus.
What is tetanic contraction?
When the motor neuron that innervates a skeletal muscle generates action potentials at an extremely rapid rate, a persistent muscular contraction known as a tetanic contraction is induced.
A motor unit has experienced its motor neuron's maximum stimulation during this state, which lasts for a while. This happens when several impulses with a high enough frequency excite the motor unit of a muscle.
Every trigger results in a twitch. A slow enough stimulus delivery will cause the muscular tension to release between each succeeding twitch. High frequency stimulation will cause the twitches to overlap, which will cause tetanic contraction.
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