It sounds too good to be true: instead of exercising, we can get fit by watching sport on television. A new study in Frontiers in Neuroscience says watching sport doesn't equate to a workout, but does raise your heart and breathing rates and increases blood flow to the skin – just like the real thing. In exercise these effects are stimulated by sympathetic nervous system activity controlling how we respond to exciting events. This response is triggered by muscles contracting in exercise or by a central response in the brain that occurs when watching it. So if watching sport is healthy, are you doing it enough?

The solution

The study, from the University of Western Sydney, was small. This may be because volunteers had fine needles stuck into nerves to measure the activity within and its impact on blood pressure and other sympathetic system effects. The nine volunteers in the study didn't show any response when watching a static screen but their heart rates and breathing increased when they saw someone running. None of the volunteers felt different and the increases, while statistically significant, were small. They were not sufficient to increase blood pressure, a measure of real physical activity.

This study does, however, support other research in suggesting that sitting is not always a wholly passive event. A study in the European Journal of Applied Physiology took four groups of volunteers ranging from competitive rowers to people aged between 50 and 60. Each was asked to imagine a rowing race while their breathing and heat rate were measured. All the groups showed increases in heart rates from 12 beats per minute in rowers to five beats in the 50 to 60 group. Competitive rowers showed the biggest difference – presumably because they could better imagine the effects.

That watching sport affects the heart is more dramatically seen from a larger, older, German study in the New England Journal of Medicine. It shows that during the 2006 World Cup finals heart attacks increased significantly among Germans watching their own team play. A match involving a penalty shoot out caused more heart attacks than games in the group stages.

So watching sport is not a passive activity – but the changes in heart rate are small and the energy expended tiny compared to moderate exercise. And other studies show increases in all causes of death from watching too much television: a BMJ Open paper suggests reducing TV watching to less than two hours a day would increase someone's life expectancy by two years. You could combine housework or gardening with imagining rowing, but even that isn't as good as turning the TV off and going for a jog or swim.