Muscle after spinal cord injury

Area of Science:

• Muscle Physiology
• Neuroscience
• Rehabilitation Science

Background:

• Spinal cord injury (SCI) profoundly impacts skeletal muscle morphology and function below the lesion level.
• Muscle adaptation post-SCI involves significant fiber-type transformation and altered contractile properties.

Purpose of the Study:

• To characterize the temporal changes in skeletal muscle fiber type, myosin heavy chain (MHC) isoforms, and oxidative capacity after SCI.
• To investigate the functional consequences of these adaptations on muscle contractile properties and fatigue resistance.

Main Methods:

• Analysis of muscle biopsies from humans and animals at various time points post-SCI.
• Assessment of myosin heavy chain (MHC) isoform expression and oxidative enzymatic activity.
• Evaluation of muscle contractile properties and fatigue resistance.

Main Results:

• A shift from slow Type I to fast glycolytic IIX fibers occurs 4-7 months post-SCI, reaching a steady state years later.
• Progressive decrease in slow MHC isoforms and increase in coexpressing fast/slow MHC isoforms observed.
• Decline in oxidative enzymatic activity and reduced muscle fatigue resistance, with faster contractile properties.

Conclusions:

• SCI induces significant, long-term skeletal muscle adaptations, including fiber-type switching and reduced oxidative capacity.
• These changes result in muscles that are faster but less fatigue-resistant.
• Longitudinal studies are crucial to establish optimal training strategies for skeletal muscle maintenance after paralysis.