An investigation of the effect of electrode size and electrode location on comfort during stimulation of the gastrocnemius muscle

The use of surface neuromuscular electrical stimulation (SNMES) in medicine is well established. However, discomfort has been identified as limiting the use of SNMES in these applications. This pilot study investigated the influence of various electrode sizes and their positioning on perceived pain and discomfort during neuromuscular electrical stimulation (NMES) of the gastrocnemius muscle using surface electrodes. This study formed part of a research project to develop a therapeutic device for calf muscle blood flow assist applications. Twelve healthy subjects (n=12) participated in this pilot study. Each participant attended the trial centre for testing which consisted of SNMES to four different electrode stimulation sites using two electrode sizes (round with areas 19.63 and 38.48 cm²). Comfort was assessed by asking the subjects to indicate the stimulation amplitude corresponding to the onset of discomfort (pain threshold) and the amplitude at which the discomfort became unbearable (pain tolerance). Of the four stimulation sites tested, two were deemed unsuccessful as it was very difficult to obtain a muscle contraction using these sites, while the remaining two sites elicited good muscle contraction. The most comfortable stimulation was achieved by placing the cathode electrode high on the calf, below the proximal end of the muscle heads and the anode electrode towards the end of the muscle belly and when the 19.63 cm² electrodes were used at these sites (p=<0.001).