Does isometric exercise result in exercise induced hypoalgesia in people with local musculoskeletal pain? A systematic review.

Objective To investigate the presence or absence of exercise induced hypoalgesia (EIH) following isometric exercise in people with local musculoskeletal symptoms. Methods Four electronic databases were searched to April 2020. Randomised controlled and crossover trials measuring effects of isometric exercise during and up to 2-hours after exercise were included. Other inclusion criteria included comparison to another intervention or healthy controls. Primary outcomes were experimentally induced pain thresholds and secondary outcomes included pain sensitivity from clinical testing. Results 13 studies with data from 346 participants were included. EIH was reported in some upper and lower limb studies but there were no consistent data to show isometric exercises were superior to comparison interventions. Only protocols that involved the quadriceps and were over 3-minutes total duration resulted in any effect on pressure pain thresholds (PPTs) or pain. Conclusions There was no consistent evidence for EIH following isometric exercise. Findings contrast healthy populations as well as conditions such as fibromyalgia with widespread symptoms. Although well tolerated, isometric exercise cannot be prescribed with certainty to induce EIH. Dose, location and intensity of protocols in this review may explain inconsistent findings, and further work is needed to determine how endogenous analgesia is affected in musculoskeletal conditions.