The effect of isometric exercise on pain in individuals with plantar fasciopathy: A randomized crossover trial

Isometric exercise is commonly recommended for immediate pain relief in individuals suffering from lower limb tendinopathies, despite the limited evidence supporting its analgesic effect. Due to the similarities between plantar fasciopathy and tendinopathies, the aim of this trial was to investigate the acute effect of isometric exercise on pain, compared to isotonic exercise, or walking, in individuals with plantar fasciopathy. We recruited 20 individuals with plantar fasciopathy for this prospectively-registered, participant-blinded, randomized, superiority crossover trial (ClinicalTrials.gov: NCT03264729). Participants attended three exercise sessions (isometric, isotonic, or walking) in a randomized order, within a 2-week period. Both isometric and isotonic exercises were performed standing with the forefoot on a step bench, while walking was performed barefoot. The primary outcome was pain (measured on a 0-100-mm VAS) during a pain-aggravating activity. Secondary outcomes included pressure pain threshold (PPT) under the heel, and plantar fascia thickness (PFT). All outcomes were measured before and after each exercise session. There were no significant differences between the three exercises on pain (P = 0.753), PPTs (P = 0.837), or PFT (P = 0.718). Further, there was no change in pain from before to after any of the exercises (isometric exercise 2.7 mm [95% CI: -12.2; 6.8], isotonic exercise -3.4 mm [95% CI: -5.0; 11.8], or walking 1.6 mm [95% CI: -16.1; 12.9]). Contrary to expectations, isometric exercise was no better than isotonic exercise or walking at reducing pain in individuals with plantar fasciopathy. None of the exercises induced any systematic analgesic effect.