Changing the Position of the Stimulating Electrode Reduces the Pain of Recording F-Waves from the Vastus Lateralis Muscle

Repetitive electrical stimulation of the femoral nerve to record F-waves from the vastus lateralis (VL) muscle can cause significant pain in some participants. This study aimed to develop a method for recording F-waves from the VL with minimal discomfort by adjusting the position of the stimulating electrode. Fifteen healthy participants were recruited. The cathode was positioned at two locations: one at the center of the thigh and the other slightly lateral to it, targeting the physiological motor point of the distal VL. The anode was placed on the lateral thigh, and the recording electrode was placed on the distal VL. F-waves were elicited at each site, with the stimulus intensity set at 1.2 times the level required to elicit the maximum M-wave amplitude. Stimulus duration was 0.2 ms, frequency was 0.2 Hz, and 30 stimuli were delivered per trial. Pain levels were immediately assessed using a visual analogue scale (VAS). The following parameters were analyzed: stimulus intensity, VAS scores, M-wave amplitude, F-wave persistence, F-wave mean latency, F-wave mean amplitude, and F/M amplitude ratio. Stimulation at the lateral site resulted in reduced stimulus intensity, VAS scores, M-wave amplitude, and F-wave persistence compared to the center site. F-wave mean amplitude and the F/M amplitude ratio were higher, while F-wave latency remained unchanged. Shifting the cathode slightly lateral to the center of the thigh enabled F-wave recordings from the VL with lower stimulation intensity and reduced pain. However, changes in M-wave and F-wave parameters were observed.