NMES for Shoulder Stability: External Rotators Are Superior
For improving shoulder stability and preventing pain, neuromuscular electrical stimulation should target the external rotators (lateral rotators) of the shoulder, not the internal rotators. This recommendation is based on high-quality guideline evidence demonstrating that external rotation range of motion is the most significant factor related to shoulder pain prevention and functional recovery 1.
Evidence-Based Rationale
External Rotator Stimulation Prevents Shoulder Pain
Electrical stimulation to improve shoulder lateral (external) rotation is specifically recommended by the American Heart Association/American Stroke Association guidelines for preventing shoulder pain in the involved upper extremity after stroke 1.
Price and Pandyan's Level I evidence demonstrated that patients receiving electrical stimulation had a significant treatment effect in favor of pain-free lateral rotation, even though pain intensity itself did not change compared to controls 1.
Bohannon et al. identified that range of lateral rotation was the factor that related most significantly to the onset/occurrence of shoulder pain 1.
Why External Rotators Matter More
Improving external rotation and abduction range of motion through stretching and mobilization is specifically recommended as a means of preventing frozen shoulder and shoulder-hand pain syndrome 1.
The 2016 AHA/ASA guidelines reiterate that gentle mobilization and stretching exercises should focus on increasing external rotation and abduction 1.
Loss of external rotation is a primary contributor to adhesive capsulitis and complex regional pain syndrome in the hemiplegic shoulder 1.
Internal Rotator Considerations
Internal rotators (subscapularis, pectoralis major) are more commonly associated with spasticity-related pain rather than instability 1.
Botulinum toxin injections into the subscapularis and pectoralis major are used to treat spasticity-related shoulder pain, not to improve stability 1.
Excessive internal rotation contributes to shoulder protraction and poor posture, which decreases vital capacity and increases work of breathing 1.
Clinical Implementation
NMES Parameters for External Rotators
Target the infraspinatus and teres minor muscles (primary external rotators) with surface or intramuscular electrodes 1.
Use tetanic frequencies (20-75 Hz) to produce fused contractions that maximize muscle tension and strength gains 1.
Apply high duty cycles (1:1 or 1:2 on:off ratio) with on-times of at least 2 seconds to evoke high muscle tension 1.
Position the shoulder in slight external rotation (not maximal) during initial sessions to avoid delayed onset muscle soreness, then progressively increase the lengthened position over weeks 1.
Implement 2-3 sessions per week for strength gains, allowing adequate recovery between sessions 1.
Common Pitfalls to Avoid
Do not use overhead pulleys, which encourage uncontrolled abduction and have the highest incidence of developing hemiplegic shoulder pain 1.
Avoid aggressive passive range of motion if done improperly, as it could cause more harm than good to the complex shoulder joint 1.
Do not neglect staff education to prevent trauma to the hemiplegic shoulder during transfers and positioning 1.
Start with lower stimulation intensity during first sessions to prevent muscle damage and gradually increase to maximum tolerable levels 1.
Supporting Evidence for NMES Efficacy
NMES is safe and well-tolerated with no serious adverse events reported and only low incidence of muscle soreness 2.
NMES produces statistically significant improvements in muscle strength (SMD 0.53,95% CI 0.19 to 0.87) and increases muscle mass 2.
Intramuscular NMES for 6 hours/day over 6 weeks showed pain differences remaining significant 12 months after treatment, particularly effective in less chronic stroke patients 1.