# Muscle Genes Linked to Natural Fitness Differ in Aging Rats Even Before Exercise

*Methylome-transcriptome integration reveals molecular signatures of intrinsic aerobic capacity in aged skeletal muscle.*

- **Evidence Level**: Preliminary
- **Why this grade**: Lab study in aged rats bred for high or low running capacity, with no duration stated and findings not yet tested in people.
- **Population**: Animal study
- **Publication Types**: Journal Article
- **Journal**: Journal of sport and health science
- **Sample Size**: Aged rats (23-24 months) bred for high or low running capacity, number not stated
- **Authors**: Zhou L, Mozaffaritabar S, Torma F, Koltai E, Kawamura T, Higuchi M, Zhong Z, Koch LG, Britton SL, Radák Z
- **Graded and published**: 2026-09-17
- **Last edited**: 2026-09-18
- **Topics**: exercise, epigenetics, muscle aging
- **DOI**: https://doi.org/10.1016/j.jshs.2026.101178
- **Original Source**: https://pubmed.ncbi.nlm.nih.gov/42754146/

## Summary

Rats born with high stamina carry a different chemical pattern on their muscle DNA as they age, before they ever run a wheel. In old rats bred for high or low running capacity, researchers mapped chemical tags on muscle DNA (methylation) and gene activity. The high-stamina rats also changed more genes after voluntary running, which may help explain why some people seem to get more out of training than others. This was rats only, and the candidate genes still need testing to see what they actually do.

## Practical Takeaway

This rat study suggests your baseline fitness may shape how your muscles respond to exercise.

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