Response of group III and IV muscle afferents to sinusoidal mechanical stimuli at different frequencies in rats. Each spot in the illustration represents the receptive field of a group III and IV muscle afferent. A: shading illustrates the tendinous area. B: representative raw recording of individual group IV fiber activity in response to a 137-mN sinusoidal mechanical stimulus at different frequencies (0.01, 0.05, 0.10, 0.20, and 0.25 Hz). C: average number of spikes evoked by a 137-mN sinusoidal mechanical stimulus at different frequencies in group III (○, n = 1) and IV (●, n = 11) fibers. D: average number of spikes per second to a 137-mN sinusoidal mechanical stimulus at different frequencies in group III (○, n = 1) and IV (●, n = 11) fibers. *P < 0.05; **P < 0.01. All data analyzed by one-way repeated-measures ANOVA followed by post hoc Fisher’s least significant difference (LSD).