Train-of-four stimulation

The train-of-four ratio (TOFR) is calculated as the ratio between the fourth twitch (T4) of the train-of-four (TOF) sequence and the first (T1).
(A) In the unblocked muscle the TOFR is 1.
(B) During a partial depolarizing block there is minimal, if any, fade such that the TOFR remains close to 1.
(C) During a partial non-depolarizing block, T4 decreases preferentially, followed by T3, then T2, and lastly, T1. The decrease in TOFR from the normal ratio of 1 is called "fade".
(D) A set of two TOF stimuli are recorded, followed by administration of rocuronium. Over the ensuing three sets of TOF stimuli, the TOFR remains at baseline (ie, TOFR 1), followed by progressive increase in fade (decrease in TOFR) from 0.81 to 0 during neuromuscular block onset.
(E) During recovery of block the TOFR increases progressively towards 1.
(F) During recovery from 1 mg/kg succinylcholine there is no significant fade in the train-of-four (TOF) response. At 8% recovery of T1 (the first twitch in the train-of-four), the TOFR was 0.89 and at 96% recovery of T1, the TOFR was 1.04.