Figure 7: Reducing the frequency of the tcVNS sine wave reduces both muscle and vagus activation thresholds.

a) Schematic diagram of the three waveform frequencies. b) Higher stimulation frequencies require greater stimulation intensities to activate the neck muscles. c) Similarly, higher frequencies have a higher threshold for vagus nerve activation. d) The ratio of the vagus nerve and muscle activation threshold was unchanged. * denotes a difference between groups with p<0.05