The Study
Effects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscle: A Systematic Review and Meta-Regression
This study is like a big summary of many smaller studies that watched people who exercised. It shows that certain types of exercise are linked to improvements in muscle energy factories and blood supply, but it can't prove that the exercise definitely caused those changes because people weren't randomly assigned to groups.
Analysis score
Maximum 100 for a systematic review with meta-analysis.
Where the score came from
This study looked at how different types of exercise help grow tiny energy factories and tiny blood vessels in muscles.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 552 / 100
Quality score
The highest quality evidence. Systematic reviews and meta-analyses that pool randomized controlled trials, giving the most reliable summary of experimental evidence.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes, this matters—better mitochondria and blood flow mean more energy, better stamina, and lower disease risk, especially for people starting from low fitness.
- 2All types of exercise—longer slow runs, fast intervals, and all-out sprints—boosted muscle energy factories by about 23–27%.
- 3Sprints gave the same boost in much less time—3.9 times more efficient than slow runs.
- 4Blood vessel number per muscle fiber went up 10–15% with all types, but only slow runs increased density because muscles didn’t get bigger.
- 5Most blood vessel growth happened in the first 4 weeks.
- 6People starting with lower fitness improved the most.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Sports Medicine (Auckland, N.z.)
Year
2024
Authors
Knut Sindre Mølmen, N. Almquist, Ø. Skattebo
Related Content
Claims (6)
Doing light, steady exercise—like a brisk walk—can boost the energy powerhouses in your muscles.
For people who aren't super fit to start with, different types of workouts—like steady cardio, intense interval training, and short sprints—boost the energy powerhouses in their muscles by about the same amount, around 23–27%.
If you're just starting to get fit, different types of workouts like steady jogging, intense intervals, and all-out sprints all help grow similar numbers of tiny blood vessels per muscle fiber. But jogging-style workouts boost blood vessel density more because they don’t make your muscles grow as much, so the vessels aren’t stretched thinner.
People who start out less fit tend to see bigger improvements in their stamina and muscle health when they begin exercising, no matter their age or gender — the lower your starting fitness, the more you gain.
Sprint workouts might boost your muscle energy factories way faster per minute than other types of exercise — about 2-4 times more efficiently than harder or longer workouts, especially if you're just starting out or somewhat active.
When people who aren't very fit start exercising, their muscles grow new blood vessels quickly in the first month, but after that, even if they keep working out, they don’t get many more new blood vessels.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.