Ageing leads to selective type II myofibre deterioration and denervation independent of reinnervative capacity in human skeletal muscle.
Level 4 - case-series / case-control
Cross-sectional observational comparison between two age cohorts
PubMed 39466960 · doi:10.1113/EP092222
What was done
Skeletal muscle biopsies were obtained from 10 healthy, lean, recreationally active young men (22 ± 3 years) and 11 older men (69 ± 3 years) matched for health status, activity level, and body mass index. Immunofluorescence was used to evaluate myofibre composition, morphology (size and shape), capillarization, satellite cell and myonuclear content, spatial relationships between satellite cells and capillaries, denervation, and myofibre grouping.
What was found
Compared with young muscle, aged muscle contained 53% more type I myofibres, and type II myofibres were 32% smaller and 3% misshapen (P < 0.05). Aged muscle exhibited 29% fewer capillaries and 38% fewer satellite cells surrounding type II myofibres (P < 0.05), while the spatial relationship between satellite cells and capillaries remained intact. Denervated myofibres were ~2.6-fold higher in older muscle (P < 0.05). Grouped type I myofibres were ~18-fold higher in aged muscle (P < 0.05), driven primarily by increased size of existing groups rather than group frequency.
Why it matters
By controlling for the confounding effects of inactivity and adiposity, these findings show that primary human ageing drives selective type II myofibre deterioration and denervation. This clarifies cellular targets for interventions aiming to counter age-related sarcopenia.
Limits
The sample size is very small (n = 21) and restricted entirely to recreationally active, healthy males, limiting generalizability to females and less healthy or sedentary populations. The cross-sectional design cannot establish longitudinal trajectory or direct causality, and functional muscle strength measures were not reported in the abstract.
Cited by
- supports There is a progressive loss of fast-twitch muscle fibers with aging, primarily due to the inherent aging process.