Relationship between changes in neuromuscular factors and disability outcomes following a resistance exercise intervention in rotator cuff tendinopathy.

BACKGROUND

Exercise is a first-line treatment for rotator cuff (RC) tendinopathy, but responses are variable. Defining mechanisms underlying patient improvement is necessary. This study investigated the relationship between neuromuscular factors-specifically peak force, rate of force development (RFD), and muscle activation onset-and patient-reported disability outcomes during an 8-week resistance exercise program.

METHODS

51 participants with RC tendinopathy underwent assessments of peak force, RFD, and EMG muscle activation onset at baseline, 2, 4, and 8 weeks. Penn Shoulder Score measured patient-reported disability. Linear mixed-effects models assessed changes over time and the association between variables.

RESULTS

Penn scores improved from baseline through weeks 2, 4, and 8. RFD increased in external rotation and abduction and peak force in external rotation and earlier EMG onset of deltoid and RC muscles. Baseline Penn score, increase in isometric abduction peak force from week 0 to week 2 and from week 2 to week 4 were associated with improved disability outcomes after controlling for pain during the task.

CONCLUSION

Several force and muscle activation variables changed after the exercise intervention, but only abduction peak force was related to patient-reported disability outcomes. This may offer added insight into individual recovery mechanisms beyond patient-reported outcomes alone.