Background & Aims
Chronic shoulder pain is a relevant musculoskeletal condition. Physical therapy for the management of chronic shoulder pain encompasses a multimodal approach, where exercise plays a significant role. Exercise-induced hypoalgesia (EIH) is characterized by a diminished sensitivity to noxious stimulation or a decrease in pain perception as a result of exercise. Although isometric exercise has been associated with the EIH phenomenon, only a small amount of research has been conducted examining the role of isometric contraction (IC) on chronic shoulder pain. Indeed, the influence of the level of intensity of IC on symptoms and function for patients with this condition is still unclear. Therefore, this study aimed to evaluate the influence of the intensity of the IC of shoulder external rotators, comparing the effect of a high-level IC (80% maximal voluntary isometric contraction – MVIC) versus a low-level IC (20% MVIC) on pain intensity, pain thresholds, and function.
Methods
This was a single-blinded, randomized study. Eighty-two patients with chronic musculoskeletal shoulder pain were allocated to two groups. Patients in group 1 (n= 41) received a five-series IC of shoulder external rotators at 20% MVIC, while patients in group 2 (n= 41) received similar protocol but the intensity of contraction was set at 80% MVIC. In both cases, each series of IC was done until exhaustion or up to a maximum of 5 minutes. Patients received five sessions of treatment for two weeks. The outcome measures included pressure pain thresholds (PPT), pain intensity (PI-NRS), and shoulder function (Constant-Murley). For each group, PPTs were assessed in three different sites, the dominant trapezius muscle (local), the non-dominant trapezius muscle (contralateral), and the dominant gastrocnemius muscle (distal). All outcomes were taken at baseline and the end of the treatment. The outcome evaluator was blinded. Data analysis was performed using the intention to treat principle.
Results
Both groups were similar at baseline. The mean age of participants was 61 years old. The two-way MANOVA did not find statistically significant differences between groups in any variable. The within-groups analysis for the 20% MVIC group showed significant differences (before-after) in Gastrocnemius PPT (mean difference 1.038 kg/cm2, p = 0.03), pain intensity (mean difference 1.20 points, p= 0.00), and function (mean difference 13.84 points, p = 0.00). Also, significant (before-after) changes were obtained in the 80% MVIC group for PPT in the dominant trapezius (mean difference of 1.050 kg/cm2, P = 0.02), pain intensity (mean difference 1.50 points, p = 0.00), and function (mean difference 14.14 points, p = 0.00). A moderate (d= 0.49) effect size (ES) was found between groups for the non-dominant trapezius PPT measure. Most of the before-after differences in pain thresholds, pain intensity, and shoulder function were deemed to be clinically meaningful (ES ranging from 0.5 to 1.16).
Conclusions
The results of the study confirm the efficacy of isometric contractions in the management of chronic shoulder pain. This study reveals that intensity (MVIC %) might not play a critical role in the hypoalgesic effect of isometric contractions. Since similar favorable effects were obtained at both intensity levels, the selection of the type of contraction (high % MVIC, low % MVIC), when performing shoulder isometric exercise, may be based on the personal preferences of the patient, or in the agreement between the therapist and patient.
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Presenting Author
Jorge Fuentes
Poster Authors
Topics
- Treatment/Management: Interventional Therapies – Other