Every runner has heard of it, most of us believe in it, and some of the lucky ones have experienced it. A new study published by Cell Press has revealed that the europhic feeling we get at the midway mark of our workout has less to do with feeling excited that we’ve almost made it and more to do with our primal instincts. The happy feeling, referred to as the runner’s high, is a response to lowered levels of the hormone leptin. Leptin is the hormone responsible for signalling to our brain that we feel satiated.

We’ve always thought that exercising on an empty stomach was cruel and unusual punishment but according to the study lowered levels of leptin, associated with being hungrier, increases our motivation for physical activity. This makes sense considering, when our ancestor’s started to feel hungry it was time for them to go hunt. Falling leptin levels send a hunger signal to the brain’s pleasure centre to generate the rewarding effects of exercising.

Previous studies have also linked low leptin levels to improved marathon times, greater running speed and also, exercise addiction. Does this mean we should start training on an empty stomach? Not quite though the study would suggest that we eat well in advance of our workout for the best results.