Another one in five people said they would be out of breath running 100 metres, according to the British Heart Foundation study.
The survey also revealed that many people felt too unfit to join a gym and many had not run a mile in over a decade.
Gaynor Burton, the founder of FitFish a Christian fitness organisation says people shouldn't feel intimidated about getting in shape: "There's all kinds of fun classes out there dance classes and things like that, it's not just about running. Find something you enjoy, start small and celebrate small successes- then enjoy the improvement that brings."
She said baby steps are the key to success: "It really is just starting small and not worrying what people think, because a lot of people will look at your with respect. There are things like the couch to 5K programme that the NHS runs that just takes you step by step to build up to run a bit further."
Lucy Wilkinson a cardiac nurse with the British Heart Foundation said: "Your heart is a muscle and like any other muscle needs to be active to be healthy and strong. We know that physical activity can help maintain a healthy weight can help lower our blood pressure and lower our cholesterol which are risk factors for cardiovascular disease."
In the run up to the London Marathon, the BHF has launched the "My Marathon" challenge asking participants to run 26.2 miles during the month of May.