Coupling between skeletal muscle fiber size and capillarization is maintained during healthy aging

Area of Science:

• Exercise Physiology
• Skeletal Muscle Biology
• Aging Research

Background:

• Muscle capillarization is vital for oxidative capacity and muscle fiber size.
• Capillary rarefaction (reduction) may contribute to sarcopenia and functional decline in older adults.
• Understanding age-related changes in muscle capillarization is crucial for maintaining health in aging populations.

Purpose of the Study:

• To investigate how aging affects muscle capillarization.
• To examine the relationship between capillary supply, muscle fiber oxidative capacity, and fiber size in young and older adults.
• To assess capillary distribution and its determinants across the lifespan.

Main Methods:

• Muscle biopsies were obtained from healthy, recreationally active young (22 years) and older (74 years) individuals.
• Muscle capillarization and capillary domain distribution were analyzed.
• Oxidative capacity of muscle fibers was measured using succinate dehydrogenase (SDH) activity.

Main Results:

• No significant age-related reduction in muscle fiber oxidative capacity was observed.
• Older adults showed type II fiber atrophy (18%) and fewer capillaries per fiber (23%).
• Despite these changes, capillary distribution and maximal oxygen consumption per capillary did not differ significantly between age groups, with fiber size being the primary determinant of capillary supply.

Conclusions:

• Healthy aging preserves the quantitative and qualitative distribution of capillaries in skeletal muscle.
• Age-related capillary rarefaction occurs but maintains the coupling between muscle fiber size and capillarization.
• This coupling suggests preserved muscle function despite some age-related fiber atrophy.