Should exercises be painful or not? Effects on clinical and experimental pain in individuals with shoulder pain.

ABSTRACT Exercise can reduce pain, however the effect of painful versus non-painful exercises is uncertain. The primary aim of this randomized cross-over study was to compare the effect of painful versus non-painful isometric shoulder exercises on pain intensity after exercise in individuals with rotator cuff-related shoulder pain (RCRSP). Secondary exploratory aims were to describe the effects on pressure pain thresholds (PPTs), conditioned pain modulation (CPM) and muscle strength. On separate days, 35 individuals performed painful isometric shoulder exercises (external rotation; 20% above pain threshold), non-painful isometric shoulder exercises (external rotation; 20% below pain threshold), and a rest condition, in randomised order. Shoulder pain intensity (VAS), PPTs, CPM, and external rotation strength were assessed before, immediately after and 45 min after conditions. No significant differences were observed between painful and non-painful exercises. VAS-scores increased immediately after both painful and non-painful exercises compared with rest (P=0.047, partial ƞ2=0.07), but were similar to pre-exercise levels after 45 minutes. No changes in PPTs, CPM or muscle strength after exercises compared with rest were observed. Painful and non-painful isometric exercises caused a moderate but short-lasting increase in shoulder pain in individuals with RCRSP. Isometric exercises had no effect on pain sensitivity and shoulder muscle strength or CPM. Perspective: This study evaluated for the first time in individuals with rotator cuff-related shoulder pain (RCRSP) the effects of painful versus non-painful isometric exercises on different pain-related outcome measures. Both painful and non-painful isometric exercises caused a moderate but relatively short-lasting increase in shoulder pain in individuals with RCRSP. Trial registration number: (ClinicalTrials.gov) NCT03675399