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Shah KM1, Safford D1, Cooper J2, Sweitzer B3, Karduna A2, McClure PW1
1Arcadia University, Physical Therapy, Glenside, United States, 2University of Oregon, Department of Human Physiology, Eugene, United States, 3Einstein Healthcare Network, East Norriton, United States
Background: Rotator cuff syndrome (tendinopathy, bursitis, tendinitis and small tears) is the most common cause of shoulder pain. Shoulder exercise and receiving a subacromial injection is the first line of treatment for these patients, and has shown to be effective in about 70% of patients. However, we currently have poor understanding of the mechanisms of how exercise leads to improvements.
Purpose: The purpose of this study is to determine the changes in rotator cuff voluntary activation (VA), i.e. central drive, after a subacromial injection, and following a 6-week exercise program, in patients with rotator cuff syndrome.
Methods: 14 patients with positive shoulder impingement tests were included in this on-going study (10F, mean age 35.1(12.5), Painful-5R). The ultimate goal is to recruit 45 patients. Patients were seated on a custom force testing apparatus. Electrodes were placed on the infraspinatus muscle to deliver a local electrical stimulation. Two isometric maximal voluntary contractions (MVCs) were collected during external rotation (ER). The patient then received the 1st brief, strong electrical impulse when they were contracting at 95% of their MVC, and a 2nd impulse at rest. The peak force from the voluntary portion of the isometric contraction, the force augmentation produced by the superimposed electrical stimulus, and the force produced by the stimulus applied to the relaxed muscle were measured and used to determine the VA (VA=1, indicates full activation of the muscle). VA data were collected at baseline (T1), after the subacromial injection (T2), and after the 6-week exercise program (T3), which included mobility, strengthening and stretching exercises. Pain rating with activity was collected at T1, T2 & T3, and self-report Penn Shoulder Score (PSS) was collected at T1 & T3.
Results: The VA increased (p=0.04) from T1 (0.23 (1.1)) to T2 (0.76 (0.52)) and remained unchanged at T3. ER peak force was not different across time points and averaged 83N (35.7) at T1 to 94.7N (46.2) at T3. Pain with activity, measured using numeric pain rating scale, was significantly reduced (p 0.01) from baseline (5 (2.1)) to after injection (2.5 (2.3)) and continued to decrease at T3 (1.6 (1.3)). The PSS changed from 61 (17.1) at baseline to 86 (13.3) at discharge.
Conclusion(s): As expected, VA was reduced at baseline and improved dramatically after the injection, suggesting that pain relief improves muscle activation. At 6-weeks post-exercise, pain with activity, and self-reported pain and function measures improved. The change in the PSS scores, 25 points, exceeded the previously published MCID of 11.4.
Implications: Understanding neural adaptations with exercise is critical to learning how to best modify the system and optimize current rehabilitation strategies, for example including exercises focused on motor-control training, biofeedback or neuromuscular electric stimulation. Next steps include examining changes with pain and exercise in the motor pattern and activation of the rotator cuff muscles using electromyography in submaximal exertion activities.
Keywords: tendinopathy, pain, rotator cuff
Funding acknowledgements: National Institute of Health, US - 1R01AR063713-01A1
Purpose: The purpose of this study is to determine the changes in rotator cuff voluntary activation (VA), i.e. central drive, after a subacromial injection, and following a 6-week exercise program, in patients with rotator cuff syndrome.
Methods: 14 patients with positive shoulder impingement tests were included in this on-going study (10F, mean age 35.1(12.5), Painful-5R). The ultimate goal is to recruit 45 patients. Patients were seated on a custom force testing apparatus. Electrodes were placed on the infraspinatus muscle to deliver a local electrical stimulation. Two isometric maximal voluntary contractions (MVCs) were collected during external rotation (ER). The patient then received the 1st brief, strong electrical impulse when they were contracting at 95% of their MVC, and a 2nd impulse at rest. The peak force from the voluntary portion of the isometric contraction, the force augmentation produced by the superimposed electrical stimulus, and the force produced by the stimulus applied to the relaxed muscle were measured and used to determine the VA (VA=1, indicates full activation of the muscle). VA data were collected at baseline (T1), after the subacromial injection (T2), and after the 6-week exercise program (T3), which included mobility, strengthening and stretching exercises. Pain rating with activity was collected at T1, T2 & T3, and self-report Penn Shoulder Score (PSS) was collected at T1 & T3.
Results: The VA increased (p=0.04) from T1 (0.23 (1.1)) to T2 (0.76 (0.52)) and remained unchanged at T3. ER peak force was not different across time points and averaged 83N (35.7) at T1 to 94.7N (46.2) at T3. Pain with activity, measured using numeric pain rating scale, was significantly reduced (p 0.01) from baseline (5 (2.1)) to after injection (2.5 (2.3)) and continued to decrease at T3 (1.6 (1.3)). The PSS changed from 61 (17.1) at baseline to 86 (13.3) at discharge.
Conclusion(s): As expected, VA was reduced at baseline and improved dramatically after the injection, suggesting that pain relief improves muscle activation. At 6-weeks post-exercise, pain with activity, and self-reported pain and function measures improved. The change in the PSS scores, 25 points, exceeded the previously published MCID of 11.4.
Implications: Understanding neural adaptations with exercise is critical to learning how to best modify the system and optimize current rehabilitation strategies, for example including exercises focused on motor-control training, biofeedback or neuromuscular electric stimulation. Next steps include examining changes with pain and exercise in the motor pattern and activation of the rotator cuff muscles using electromyography in submaximal exertion activities.
Keywords: tendinopathy, pain, rotator cuff
Funding acknowledgements: National Institute of Health, US - 1R01AR063713-01A1
Topic: Musculoskeletal: upper limb
Ethics approval required: Yes
Institution: Arcadia University
Ethics committee: Institutional Review Board
Ethics number: 11976
All authors, affiliations and abstracts have been published as submitted.
