Effects of prolonged and acute muscle pain on the force control strategy during isometric contractions

Musculoskeletal pain is associated with multiple adaptions in movement control. This study aimed to determine whether changes in movement control acquired during acute pain are maintained over days of pain exposure. On day-0, the extensor carpi radialis brevis (ECRB) muscle of healthy participants was injected with nerve growth factor (NGF) to induce persistent movement-evoked pain (N=13) or isotonic saline as a control (N=13). On day-2, short-lasting pain was induced by injection of hypertonic saline into ECRB muscles of all participants. Three-dimensional force components were recorded during submaximal isometric wrist extensions on day-0, day-4, and before, during, and after saline-induced pain on day-2. Standard deviation (variation of task-related force) and total excursion of center of pressure (variation of force direction) were assessed. Maximal movement-evoked pain was 3.3±0.4 (0-10 numeric scale) in the NGF-group on day-2 whereas maximum saline-induced pain was 6.8±0.3 cm (10-cm visual analogue scale). The difference in centroid position of force direction relative to day-0 was greater in the NGF-group than controls (P<0.05) on day-2 (before saline-induced pain) and day-4, reflecting changes in tangential force direction used to achieve the task. During saline-induced pain in both groups, tangential and task-related force variation was greater than before and after saline-induced pain (P<0.05).