What are the stimulation parameters that affect the extent of twitch force potentiation in the adductor pollicis muscle?

Muscle force potentiation affects force output during electrical stimulation. Few studies have examined stimulation train parameters that influence potentiation such as pulse number, stimulation frequency, train duration, and force–time integral and peak force produced during the train. Pulse-matched trains (100 pulses) at 7.5, 15, 25, 30, 50, and 100 Hz, and trains of varying pulse number (50, 100, and 200 pulses) at 30 and 50 Hz were delivered to the ulnar nerve of 10 (5 male, 5 female; 23.4 ± 0.9 years), healthy individuals in random order. Single twitches of the adductor pollicis muscle were elicited before and after each train with a rest interval of at least 5 min between each train. No differences in potentiation occurred across the pulse-matched trains at frequencies of 15–50 Hz (38.9 ± 5.4–44.6 ± 5.5%). Twitch force potentiation following the highest (100 Hz) and lowest (7.5 Hz) frequency trains were not significantly different and were lower than the other 100 pulse-matched trains. As pulse number increased, potentiation increased for both the 30 and 50-Hz trains. There was a significant positive correlation between force potentiation and force–time integral produced by the stimulation train, r = 0.70. The results indicate that potentiation magnitude is dependent on the force–time integral produced during the test train and the number of pulses delivered, independent of stimulation frequency.