Measuring low frequency fatigue with 2 Hertz stimulation. II. Muscle fatigue results

For pt.I see ibid., p.1207-8 (1995). The aim of this study was to use 2 Hz electrical stimulation of the muscle to determine whether low frequency fatigue (LFF) could be measured in the finger flexor muscles at brief, low levels of exertion. Six subjects exerted sub-maximal static contractions of 5%, 10%, and 15% MVC with their ring finger against a force transducer for durations of 5, 10 and 15 minutes (9 experimental conditions). Muscle twitch forces were measured before exercise; after exercise; and 30, 60, 120, 180, 240 minutes into the recovery period. LFF was considered to be present when twitch forces fell significantly below the initial, pre-exercise levels and subsequently recovered. Minimum twitch forces were typically measured between 30 and 60 minutes into the recovery period, not immediately after exercise. Twitch forces typically took at least 120 minutes to recover, a characteristic of LFF. Significant levels of LFF were measured in all the experimental conditions except for 5 minute contractions of 5% and 15% MVC. Two Hz stimulation can reliably be used to measure LFF in forearm muscles during brief, low level static contractions