Differences in Trapezius Muscle H-Reflex between Asymptomatic Subjects and Symptomatic Shoulder Pain Subjects

Area of Science:

• Neuroscience
• Musculoskeletal Rehabilitation
• Biomedical Engineering

Background:

• Chronic shoulder pain is linked to nervous system adaptations, potentially affecting motoneuron excitability.
• These neural changes may impair scapular muscles, perpetuate pain, and hinder rehabilitation outcomes.

Purpose of the Study:

• To compare trapezius neural excitability between individuals with and without chronic shoulder pain.
• To investigate differences in H reflex parameters as indicators of neuromuscular control.

Main Methods:

• A cross-sectional study involving 12 symptomatic and 12 asymptomatic participants.
• Evoked H reflexes and M-waves in trapezius muscle parts via C3/4 and accessory nerve stimulation.
• Calculated H reflex latency, amplitude, M-wave characteristics, and their ratio.

Main Results:

• H reflexes were elicited less frequently in symptomatic (42-58%) versus asymptomatic (58-75%) groups.
• Symptomatic group showed a smaller H reflex/M-wave ratio in the upper trapezius.
• Longer H reflex latency was observed in the lower trapezius of the symptomatic group (p < 0.05).

Conclusions:

• Chronic shoulder pain is associated with altered trapezius H reflex parameters.
• These findings underscore the importance of considering trapezius neuromuscular control in rehabilitation strategies for shoulder pain.