A small but significant study of identical twins* who did the same levels of activity as kids, but developed different exercise habits later in life, has provided interesting insights into the effects that exercise has on people’s health.

Twins are valuable for research as they share the same DNA – and it’s our genes that determine our capacity and willingness to work out, as well as how our bodies react. In this case, the twins also had a similar upbringing.

FitFatTwin study
The so-called ‘FitFatTwin’ study, by the University of Jyväskylä in Finland, was based on 10 pairs of identical twin men aged 32–36. One twin exercised two or more times a week, while his brother only exercised two times a month or less. But both still had similar diets.

Over the course of three years, extensive physical measurements were recorded in the twins, including fitness levels, body composition and glucose levels/insulin sensitivity.

Brain scans were also conduced – a novel aim of the study was to analyse the difference in grey matter.

Active vs non-active
As expected, the study found the active twins had better cardiovascular fitness. Similar associations were not found for muscular strength, however, which was put down to the fact that participants mostly took part in aerobic sport.

Although the inactive twins weighed only slightly more, their percentage of body fat was “markedly higher”.

So far so unsurprising, but the university researchers also found insulin and glucose biomarkers which suggested the inactive twins had a greater risk of developing type 2 diabetes later in life.

When analysing the brain scans, the researchers also found an “extensive difference” in the volume of grey matter in favour of the physically active. The parts of the brain associated with co-ordination, motor control and cognitive function were particularly affected, the study showed.

*Kujala UM et al. Physical activity, fitness, glucose homeostasis, and brain morphology in twins. Medicine & Science in Sports & Exercise. March 2015