Figure 6. Group data showing normalized EMG responses in biceps and triceps during elbow flexion or elbow extension to an EMG target.

Responses are shown before (baseline), during (pain) and after (recovery) activation of group III and IV muscle afferents produced by infusion of hypertonic saline. All responses were evoked during contractions performed to EMG targets corresponding with the EMG produced during contractions of 20% MVC in either flexion or extension for each subject. Mean area (±s.e.m.) of responses to stimulation of the motor cortex (MEP, ○) and the corticospinal tract (CMEP, •), expressed as a proportion of the mean response prior to the infusion (i.e. at baseline). The ratio of the MEP to the CMEP is also shown (▵). Upper and lower panels are responses during flexion and extension, respectively. A and B, MEPs and CMEPs in biceps and triceps during elbow flexion (n = 6). C and D, responses in biceps (n = 5) and triceps (n = 6) during elbow extension. An infusion of hypertonic saline (○, •, ▵ and continuous lines) produced a mean pain intensity rating of 4 out of 10 (‘moderate’ pain) which returned to 0 before the recovery sets. A control infusion of isotonic saline (n = 6; □, ▪ and dashed lines) produced no perceived pain and did not alter MEPs or CMEPs. *P < 0.05, MEPs different to baseline. #P < 0.05, CMEPs different to baseline. ‡P < 0.05, MEPs/CMEPs different to baseline.