Cortical Somatosensory Excitability Is Modulated in Response to Several Days of Muscle Soreness

Changes in excitability of the sensorimotor cortex have been demonstrated in clinical musculoskeletal pain, although the timing is unknown. Eccentric exercise provokes delayed-onset muscle soreness providing a model to study the temporal profile of sensorimotor cortical plasticity during progressively developing muscle soreness. Twelve healthy participants performed eccentric exercise of the wrist extensors. Likert pain scores, pressure pain thresholds at the extensor carpi radialis (ECR) muscle, somatosensory evoked potentials from electrical stimulation of the radial nerve, maximal wrist extension force, and ECR motor evoked potentials to transcranial magnetic stimulation were recorded before (baseline) and at 2 hours (2-h post), 2 days (day 2), and 6 days (day 6) after exercise. Compared with baseline, 1) the Likert pain score was increased at 2-h post and increased further at day 2 (P < .01); 2) the ECR pressure pain thresholds were decreased at day 2 (P < .001); 3) the P45 amplitude of the somatosensory evoked potential from central-parietal recording sites was increased at day 2 (P < .001); 4) maximal wrist extension force was reduced 2-h post and at day 2 (P < .002); and 5) the cortical area from which ECR motor evoked potentials could be elicited was reduced at 2-h post and at day 2 (P < .03). A decrease in the ECR pressure pain thresholds was correlated (P < .027) with an increase in the P45 amplitude at a centroparietal recording site.

Perspective

These novel data demonstrate that the somatosensory cortical excitability may be affected by muscle soreness developing over days in parallel with a deficit in the motor system. Cortical neuroplasticity may thus develop in the subacute phase and be relevant for understanding neural adaptation in the transition from acute to persistent pain.