Been there. But according to several studies, that's not so bad after all - in fact, the simple act of thinking about exercise can trick your body into thinking you've actually done it. Why did nobody tell us this sooner?
According to Jim Davies, professor of cognitive psychology at Carleton University in Canada, "mental practice is one of the few effective performance enhancing activities." "When you imagine exercising, your breath and heart rate actually increase," he writes in Nautilus. He cites numerous studies, from a recent paper in the June 2016 edition of Frontiers in Human Neuroscience to a 2014 study where researchers asked people whose arms were in casts to imagine flexing their wrists and found that once the casts came off, those people's muscles were twice as strong as others who hadn't imagined flexing.
How? Davies, and his colleagues, put it down to proprioception, which is the sense we all have of knowing where each of our body parts is and what each one is doing, without having to see it. "Because it's a sense, just like hearing and seeing, you can have mental imagery specific to it," Davies explains.
Just don't go cancelling that gym membership just yet: Davies is the first to caution that imaginary exercise isn't as good as the real deal. Instead, he says it's a supplement to actually working out, noting, "By just using our imagination, we can improve ourselves for real."