An alien visitor to our planet would be perplexed by modern human life, not least our relationship with physical exertion. After 6 million years of hunter-gatherer existence, humans can be observed sheltering in warm rooms, counteracting the tiresome effects of earth’s gravity by slouching on comfortable seats in front of glowing screens, being whisked effortlessly between floors aboard mechanical staircases, even soaring across continents while seated in warm moving boxes. Confusingly, however, a proportion of these same humans could later be spied spending their ‘free time’ running around outside in all weathers for no apparent reason or, stranger still, handing over money to an institution called ‘the gym’ to pass time repeatedly picking up and putting down heavy objects or running on a revolving mat until they were red and sweaty.
How would we explain this peculiarly binary behaviour to our inter-planetary visitor? We might start by describing the ‘globesity’ pandemic where inactivity is estimated to cause 9% of premature mortality worldwide.1 We could extol the virtues of exercise, …