Atrophy of calf muscles by unloading results in an increase of tissue sodium concentration and fat fraction decrease:...

Area of Science:

• Musculoskeletal research
• Medical imaging
• Physiology

Background:

• ²³Na MRI reveals elevated tissue sodium concentrations in various pathologies.
• Muscle atrophy, caused by unloading, may alter extracellular volume and sodium levels.

Purpose of the Study:

• To investigate the effect of calf muscle unloading on muscle volume and tissue sodium concentration.
• To test the hypothesis that unloading leads to decreased muscle volume and increased sodium concentration.

Main Methods:

• 12 healthy males underwent 60-day lower leg unloading using an orthosis.
• ²³Na MRI and 2D PD-weighted Dixon turbo spin echo were performed on both legs.
• Sodium reference phantoms with varying NaCl concentrations were used for quantification.

Main Results:

• Unloading significantly increased tissue sodium concentration (TSC) in multiple calf muscles (10-17.4%).
• Muscle volume decreased in the medial gastrocnemius (-5.4%) and soleus (-7.8%) muscles.
• No significant changes in TSC were observed in the control leg.

Conclusions:

• Muscle unloading atrophy is linked to increased muscle sodium concentration.
• ²³Na MRI is effective in detecting subtle changes in muscle sodium concentration.