Table 3. Evidence for Motor Unit Firing Frequency. Author Participants Vibration Method (type) Exercise Type Frequency(Hz) Amplitude (mm) Duration Results Bongiovanni and Hagbarth, 1990 5 H ♀ (♂, ♀ = NR) Direct vibration dorsiflexor muscles SS 150 1.5 20-25 s Vibration had no effect on firing frequency of non-fatiguing muscle, however vibration caused an increase in EMG, force and firing frequency during fatiguing isometric maximal voluntary contractions. Griffin et al., 2001 7 H (3♂, 4♀) Direct Vibration triceps & biceps brachii Isometric 110 3 2 s every 10 s The firing frequency of the triceps significantly increased when vibration was applied during 20% MVC = Healthy; = Static squat; = Maximal voluntary contraction