Muscle fiber type diversification during exercise and regeneration

• Skeletal muscle contains fiber types with varied structural and metabolic properties.
• Muscle fibers have markedly different responses to endurance and resistant exercises.
• ROS generated by the contracting muscle can modulate force and fatigue properties.
• An optimal level of ROS is required for maximal force production.
• Eccentric exercise-related injuries are more frequent in type II fibers.
• Therapeutic strategies for muscle wasting should focus on exercise interventions.

The plasticity of skeletal muscle can be traced down to extensive metabolic, structural and molecular remodeling at the single fiber level. Skeletal muscle is comprised of different fiber types that are the basis of muscle plasticity in response to various functional demands. Resistance and endurance exercises are two external stimuli that differ in their duration and intensity of contraction and elicit markedly different responses in muscles adaptation. Further, eccentric contractions that are associated with exercise-induced injuries, elicit varied muscle adaptation and regenerative responses. Most adaptive changes are fiber type-specific and are highly influenced by diverse structural, metabolic and functional characteristics of individual fiber types. Regulation of signaling pathways by reactive oxygen species (ROS) and oxidative stress also plays an important role in muscle fiber adaptation during exercise. This review focuses on cellular and molecular responses that regulate the adaptation of skeletal muscle to exercise and exercise-related injuries.