Luckily for us a group of American scientists from the City University of New York have done the honourable thing and dedicated their brains to working out exactly how much exercise is really worth doing.
And the results, published in the Current Biology journal, may surprise you.
According to the research, which measured the daily activity levels of 300 men and women, those gym bunnies who spend hours pumping iron every week are actually wasting their time.
The study shows that over time our bodies adapt to higher activity levels – so the more you do, the less affect it has on how many calories you burn.
Those who go to the gym twice a week were found to burn on average 200 more calories than their couch-potato peers.
However, those who passed the 'sweet spot' of twice a week were actually passing the threshold of productivity.
Sorry guys, that extra time on the treadmill might have caused a lot of sweat, but perhaps not a lot of slimming.
Lead scientist Dr Herman Pontzer said; 'The most physically active people expended the same amount of calories each day as people who were only moderately active.'
So there you have it – those with moderately active lifestyles were found to shed just as many calories as those hitting the gym all week long.
And just in case you're trying to work out whether your current exercise regime of chasing after the kids and running around Sainsbury's counts as 'moderate', Herman says; 'Moderate lifestyles involve walking or cycling to work, taking the stairs rather than the lift and a couple of bursts of exercise, such as gym trips during the week.'
This theory also explains why those trying to shape up might hit a 'plateau' in their weight loss caused by dieting and exercising – your body is adapting to the new lifestyle and it sadly has less impact on those wobbly areas.
We might spend tonight on the sofa then!