Functional and structural changes after disuse of human muscle

Area of Science:

• Orthopedics
• Sports Medicine
• Physiology

Background:

• Unilateral leg fractures require immobilization, potentially leading to disuse atrophy.
• Recovery involves regaining function and muscle mass after cast removal.

Purpose of the Study:

• To quantify changes in leg volume, muscle fiber size, and oxygen uptake after unilateral leg fracture.
• To investigate the relationship between structural and functional deficits in the injured leg.

Main Methods:

• Anthropometric measurements of leg volume.
• One-leg cycling to assess maximum oxygen uptake.
• Percutaneous needle biopsy of vastus lateralis for muscle fiber analysis (myosin adenosine triphosphatase staining).

Main Results:

• Injured leg volume reduced by 12% compared to the uninjured leg.
• Maximum oxygen uptake decreased by approximately 17% in the injured leg.
• Muscle fiber cross-sectional area decreased by 42% in the vastus lateralis, affecting both Type I and Type II fibers.

Conclusions:

• Leg fracture and immobilization result in significant muscle atrophy and functional deficits.
• Discrepancies exist between gross functional/structural measurements and cellular-level changes.
• Further research is needed to understand the implications of these cellular changes on long-term recovery.