The Sedentary Twins Had "Lower Endurance Capacities, Higher Body Fat Percentages, and Signs of Insulin Resistance, Signaling the Onset of Metabolic Problems."

Identical twins in Finland who shared the same sports and other physical activities as youngsters but different exercise habits as adults soon developed quite different bodies and brains, according to a fascinating new study that highlights the extent to which exercise shapes our health, even in people who have identical genes and nurturing.

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It turned out that these genetically identical twins looked surprisingly different beneath the skin and skull. The sedentary twins had lower endurance capacities, higher body fat percentages, and signs of insulin resistance, signaling the onset of metabolic problems. (Interestingly, the twins tended to have very similar diets, whatever their workout routines, so food choices were unlikely to have contributed to health differences.)

The twins’ brains also were unalike. The active twins had significantly more grey matter than the sedentary twins, especially in areas of the brain involved in motor control and coordination.

-from "One Twin Exercises, the Other Doesn't" in the March 4, 2014 digital edition of the NYT.

The study is published in the March 2015 Medical & Science in Sports & Exercise Journal.  The abstract is here.

I like the reference to more  "grey matter."  I need all of that I can get.  And I'm hoping this also applies to people who exercise but don't have a sedentary twin.

Hard Physical Effort a Condition of Normalcy and a Demand of Design

Over and above any consideration of performance for sports, exercise is the stimulus that returns our bodies to the conditions for which they were designed.  Humans are not physically normal in the absence of hard physical effort.

-Mark Rippetoe in Starting Strength - Basic Barbell Training (3rd Ed. 2013),  p. 1.