Impact of isometric and concentric resistance exercise on pain and fatigue in fibromyalgia

Purpose The aim of this study was to determine the local and systemic effects of isometric and concentric muscle contractions on experimental pain and performance fatigability in people with and without fibromyalgia. Methods Forty-seven fibromyalgia (FM: 51.3 +/- 12.3 year) and 47 control (CON: 52.5 +/- 14.7 year) participants performed submaximal isometric and concentric exercise for 10 min with the right elbow flexors. Assessments before and after exercise included pressure pain thresholds (PPT) of the biceps and quadriceps, central pain summation, self-reported exercising arm and whole-body pain, and maximal voluntary isometric contraction (MVIC) of the right elbow flexors and left handgrip. Results People with FM experienced greater reductions in local fatigue (right elbow flexor MVIC: CON: - 4.0 +/- 6.7%, FM: - 9.8 +/- 13.8%; p = 0.013) and similar reductions in systemic fatigue (left handgrip MVIC: - 6.5 +/- 10.2%; p < 0.001) as CON participants, which were not different by contraction type nor related to baseline clinical pain, perceived fatigue, or reported pain with exercise. Following exercise both groups reported an increase in PPTs at the biceps (pre: 205.5 +/- 100.3 kPa, post: 219.0 +/- 109.3 kPa, p = 0.004) only and a decrease in central pain summation (pre: 6.8 +/- 2.9, post: 6.5 +/- 2.9; p = 0.013). FM reported greater exercising arm pain following exercise (CON: 0.7 +/- 1.3, FM: 2.9 +/- 2.3; p < 0.001), and both groups reported greater arm pain following concentric (isometric: 1.4 +/- 2.0, concentric: 2.2 +/- 2.9; p = 0.001) than isometric exercise. Neither group reported an increase in whole-body pain following exercise. Conclusion People with FM experienced greater performance fatigability in the exercising muscle compared to CON that was not related to central mechanisms of fatigue or pain. These results suggest changes in performance fatigability in FM may be due to differences occurring at the muscular level.