This can lead to sustained or tetanic contraction. Phase 1 block does not show fade under tetanic stimulation. In some cases, depression can be observed instead of potentiation following the tetanic stimulus. If stimuli are delivered at high frequency, the twitches will overlap, resulting in tetanic contraction. During tetanic contractions, muscles can shorten, lengthen or remain constant length. In some cases, diarrhea is very severe, and at times the convulsions are markedly tetanic. A fused tetanic contraction is the strongest single-unit twitch in contraction. The average tetanic tension after applying calciseptine was slightly higher than the control value. A tetanic contraction can be either unfused (incomplete) or fused (complete). Tetanic contraction is usually normal (such as when holding up a heavy box).