Latent period of muscle twitch is 10 s, contraction period is 40 s and the relaxation time is 50 s. Tetanising frequency would be:

For tetanus to occur, stimulus must fall repeatedly in the contraction phase that will cause the accumulation of Ca++ in myoplasm leading to sustained contraction. Tetanising frequency = 1 / time of contraction phase = 1/40 = 25 Hz