Effects of aging and BMI level on relationships between skeletal muscle fibers, capillaries, and mitochondria

This review focuses on body mass index (BMI) to clarify the characteristics of sarcopenic obesity from the perspective of muscle fibers (energy intake), capillaries (energy transport), and mitochondria (energy production). Fast-twitch muscle fibers are more susceptible to aging than slow-twitch fibers. The number of capillaries and mitochondrial function decrease as muscle atrophy progresses with age. However, these age-related changes are offset by changes in muscle fiber size. Interestingly, there is a proportional relationship between muscle fiber size and capillary number regardless of BMI level or age. There is a high degree of plasticity in mitochondrial structure and function in response to metabolic demands. Therefore, further research is needed to determine whether age-related mitochondrial changes are inevitable or can be prevented by exercise. In conclusion, while age-related atrophy and functional decline in fast-twitch muscle fibers maintain a balance with capillaries and mitochondria, BMI levels do not significantly affect this relationship. These findings suggest a need to re-evaluate our understanding of sarcopenic obesity, particularly the notion that excess fat exacerbates sarcopenia.