Rotator cuff tendinopathy (RC) is a common disorder of the shoulder complex, affecting approximately 24% of the Brazilian population over 20 years of age. One of the treatment strategies is conservative, including the use of therapeutic exercise. Most studies that evaluated the effect of exercise on this public have used isotonic exercises (which involve concentric and eccentric phases of muscle contraction), and few studies have demonstrated the effect of isometric exercise on individuals with RC tendinopathy. It is known that exercise, in general, has an analgesic effect described as exercise-induced analgesia. It has also been demonstrated that isometric exercise has the effect of decreasing pain summation. In addition, individuals with patellar tendinopathy showed a decrease in pain level immediately after using isometric exercise compared to isotonic exercise.

To compare the immediate and 6-week effects of isometric and isotonic exercise training on shoulder pain, function, and strength in individuals with RC tendinopathy.

This is a randomized clinical trial. 30 individuals with RC tendinopathy were included, randomly distributed in the isometric (IM = 14) and isotonic (IT = 16) groups and evaluated for pain during arm elevation using the numeric pain rating scale, function using the Penn Shoulder Score questionnaire and isometric strength through manual dynamometry. After the initial evaluation (EV1) individuals performed the first exercise session, then they were reassessed immediately after the intervention (EV2) and after 6 weeks of treatment (EV3). Individuals performed stretching and strengthening of the scapular musculature, in addition to specific exercise for the RC, being isometric or isotonic depending on the randomization, twice a week for 6 weeks. RC strengthening included shoulder flexion, external and internal rotation exercises with load reassessment and progression. Comparison between groups and the 3 assessments was performed using a linear mixed model using SPSS 22.0 software.

There was interaction between group and assessment for shoulder flexion strength (F = 5.31, p<0.05) and external rotation (F = 5.82, p<0.05). The IM showed a higher mean for flexion strength in EV3 compared to EV2 and greater rotation strength in EV3 compared to EV2 and EV1, in addition to being greater than the IT in EV3. Pain decreased and there was an improvement in function in EV3 in both groups (p>0.05).

Isometric exercise was not superior to isotonic for pain and function variables, but it was superior in terms of increasing shoulder elevation and external rotation strength.

In individuals with RC tendinopathy, the choice of exercise modality will not influence the improvement of pain or function, thus choosing the most tolerable one for the patient. However, in cases where there is a decrease in isometric strength, one can choose to use isometric exercise to increase strength gain.