Figure 4. Effect of one tetanic stimulation period on subsequent twitch responses.

Each fibre was subjected to a 400 ms period of 50 Hz stimulation (20 pulses) and then the twitch response examined ∼3 s later and then successively at 2 s intervals. When Cl⁻ was present (A), the first twitch response after the 50 Hz train was only slightly reduced, but when Cl⁻ was absent (B) the twitch response initially was almost completely abolished and then recovered to the pre-stimulation level only after a total of ∼11 s. C, mean (±s.e.m.) of twitch size for the sequence of twitch stimuli following the 50 Hz stimulation, normalized by the twitch size beforehand, in 5 fibres with Cl⁻ present and 5 fibres with Cl⁻ absent, examined with fibres from contralateral muscles alternately.