Identical twins, 30 years apart in training
At 52, the endurance-trained twin had a higher VO₂max, less body fat and more slow-twitch fibres, but less muscle size and strength than his untrained brother.
What they studied
- Design
- Case study
- People
- One pair of identical male twins, age 52
- Contrast
- More than 30 years of endurance training vs no regular exercise
- Measures
- Blood, heart and lung health, muscle size, strength, power, biopsies
What they found
- The trained twin had a 12.4 ml/kg/min higher VO₂max and 8.6% lower body fat.
- He also had lower resting heart rate, blood pressure, cholesterol, triglycerides and blood glucose.
- His muscle had 55% more slow-twitch (type I) fibres and fewer fast-twitch IIa fibres.
- But his muscle size and strength were lower, and muscle quality poorer, than his untrained brother’s.
How strong is the evidence
Case study · 1 twin pair
What this design cannot tell us:
- One pair of twins: a vivid example, not proof that applies to everyone.
- The twins also differed in other habits that were not controlled.
What it means for your training
- Genes set the starting line, not the finish. Training reshaped heart, blood and muscle.
- Endurance alone did not protect muscle size or strength. Pair it with strength work to keep both.
Our summary of the published abstract. Read the original paper for full details.