healthHealth and Medicinehealthhealth

Identical Twins – A Truck Driver And A Triathlete – Answer Part Of The Nature-Nurture Debate


Tom Hale

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

Senior Journalist

The moral of this story: "[Y]our genes aren't a cop-out," said study author Jimmy Bagley. skeeze/Pixabay (CC0 1.0)

Two identical twins have led two extremely different lives. Thanks to the fact this odd couple share over 99 percent of their DNA, their bodies are giving scientists a massive insight into the relationship between genetics and health, all while helping to answer the old-age question of whether nature or nurture is more important to our fitness.

The new study, published in the European Journal of Applied Physiology, tells the story of two 52-year-old males. One had spent the past 30 years training as an Ironman triathlete, but the other chose the much more sedentary lifestyle of a truck driver.


Scientists led by the San Francisco State University studied their physiques, blood profiles, cardiovascular and pulmonary health, skeletal muscle size, strength and power, and muscle health.

So, what's the moral of this story?

"It shows your genes aren't a cop-out," study author Jimmy Bagley, an assistant professor of kinesiology, explained in a statement.

"If your parents are overweight, for example, it might be harder for you to get fit, but this study shows that it's not impossible."


Unsurprisingly, the athletic twin exhibited much better overall health: lower body fat, lower resting heart rate and blood pressure, lower cholesterol, triglycerides, and blood sugar, and greater aerobic capacity and endurance. However, unexpectedly, the truck driver twin did appear to have considerably larger and stronger leg muscles.

“The untrained twin had been carrying around more weight his whole life, which can build bigger muscles,” said Bagley.

One of the clearest indicators of overall health is the VO2 max, the measurement of the maximum amount of oxygen that an individual can utilize during an intense workout, which accounts for cardiovascular health, pulmonary health, and muscle efficiency.

The truck driver twin's VO2 max was more-or-less typical for a man in his 50s. On the other hand, the athletic twin's VO2 max was equal to that of a 30-year-old.


“VO2 max starts to drop off at age 65 or 70, and when it hits a certain low you are probably going to become dependent on someone else," added Bagley. "As people get older, we try to keep them over that dependency limit."

On top of all that, the super-active twin had 55 percent more "slow-twitch" muscle fibers that help with endurance activities like long distance running, cycling, and swimming. In the words of the researchers, “he was like a machine.”

You’ll be pleased to hear that the research has led the truck driver to start walking as a hobby. The scientists will continue to study this unlikely duo every five years as they age to gain deeper insights into the slippery nature of genetics, lifestyle, health, and fitness.


healthHealth and Medicinehealthhealth
  • tag
  • muscle,

  • nature,

  • fitness,

  • health,

  • twin,

  • nurture,

  • twin study,

  • identical twin