Differences in shoulder muscle activity between patients with generalized joint laxity and normal controls

Area of Science:

• Biomechanics
• Musculoskeletal Research
• Sports Medicine

Background:

• Generalized joint laxity is associated with shoulder instability.
• Understanding the neuromuscular control of the shoulder is crucial for managing instability.

Purpose of the Study:

• To analyze shoulder muscle electromyographic (EMG) activity in patients with generalized joint laxity and shoulder instability.
• To compare this activity with that of healthy individuals.
• To elucidate the neuromuscular mechanisms underlying shoulder instability in this population.

Main Methods:

• Surface and intramuscular fine-wire electrodes were used to record EMG activity from eight shoulder muscles in six patients.
• Muscles recorded included subscapularis, supraspinatus, infraspinatus, pectoralis major, deltoid (anterior, middle, posterior), and latissimus dorsi.
• EMG signals underwent low-pass filtering, full-wave rectification, time-averaging, and normalization for comparative analysis.

Main Results:

• Patients exhibited significantly decreased muscle activity in the anterior and middle deltoid during abduction and flexion.
• Increased subscapularis activity was observed during internal rotation in patients.
• Co-contraction of agonist and antagonist muscles was present in patients, similar to healthy subjects.

Conclusions:

• Altered shoulder muscle activity patterns are evident in individuals with generalized joint laxity and shoulder instability.
• These findings provide a foundation for understanding the biomechanical basis of shoulder instability.
• The results support the development of targeted physical training programs for patients with generalized joint laxity and shoulder instability.