Structural changes in male trapezius muscle with work-related myalgia

Area of Science:

• Occupational health
• Muscle physiology
• Biomedical science

Background:

• Work-related neck and shoulder myalgia is prevalent in certain occupations.
• Understanding the underlying muscular changes is crucial for prevention and treatment.

Purpose of the Study:

• To investigate muscular alterations in male forest machine operators experiencing work-related neck and shoulder myalgia.
• To compare muscle characteristics between myalgic operators, non-myalgic operators, and healthy controls.

Main Methods:

• Muscle biopsies were obtained from three groups: myalgic operators (M), non-myalgic operators (NM), and healthy controls (C).
• Enzyme cyto- and immunohistochemical analyses were performed on the muscle samples.

Main Results:

• The myalgic group (M) showed a significant increase in type IIA muscle fibers compared to controls (C), with a parallel increase in the capillary bed.
• Both myalgic (M) and non-myalgic (NM) groups exhibited increased fibers with disorganized mitochondrial patterns.
• Fibers lacking cytochrome c oxidase were observed in both M and NM groups, suggesting potential mitochondrial defects.

Conclusions:

• The observed muscle changes, including type IIA fiber hypertrophy and mitochondrial disorganization, are associated with work-related trapezius myalgia in forest machine operators.
• These alterations likely result from injury-regeneration cycles induced by occupational demands.
• The presence of mitochondrial defects warrants further investigation into their role in myalgia development.