Effect of Two Contrasting Interventions on Upper Limb Chronic Pain and Disability: A Randomized Controlled Trial

Background: Chronic pain and disability of the arm, shoulder, and hand severely affect labor market participation. Ergonomic training and education is the default strategy to reduce physical exposure and thereby prevent aggravation of pain. An alternative strategy could be to increase physical capacity of the worker by physical conditioning. Objectives: To investigate the effect of 2 contrasting interventions, conventional ergonomic training (usual care) versus resistance training, on pain and disability in individuals with upper limb chronic pain exposed to highly repetitive and forceful manual work. Study Design: Examiner-blinded, parallel-group randomized controlled trial with allocation concealment. Setting: Slaughterhouses located in Denmark, Europe. Methods: Sixty-six adults with chronic pain in the shoulder, elbow/forearm, or hand/wrist and work disability were randomly allocated to 10 weeks of specific resistance training for the shoulder, arm, and hand muscles for 3 x 10 minutes per week, or ergonomic training and education (usual care control group). Pain intensity (average of shoulder, arm, and hand, scale 0 – 10) was the primary outcome, and disability (Work module of DASH questionnaire) as well as isometric shoulder and wrist muscle strength were secondary outcomes. Results: Pain intensity, disability, and muscle strength improved more following resistance training than usual care (P < 0.001, P = 0.05, P < 0.0001, respectively). Pain intensity decreased by 1.5 points (95% confidence interval -2.0 to -0.9) following resistance training compared with usual care, corresponding to an effect size of 0.91 (Cohen’s d). Limitations: Blinding of participants is not possible in behavioral interventions. However, at baseline outcome expectations of the 2 interventions were similar. Conclusion: Resistance training at the workplace results in clinical relevant improvements in pain, disability, and muscle strength in adults with upper limb chronic pain exposed to highly repetitive and forceful manual work. Trial registration: NCT01671267. Key words: Musculoskeletal pain, workability, shoulder pain, elbow pain, tennis elbow, wrist pain