Nearly half of UK adults admit getting out of breath when running for a bus, according to a new poll.
Research by the British Heart Foundation (BHF) found some 48% of women and 42% of men confessed to feeling so unfit they would get short of breath if they had to run to catch public transport.
The survey also found 47% felt they could run up to just half a mile, while one in five said they could only manage 100 metres.
Even of those who believed they could run a mile, three in 10 (29%) said they had last done so more than a decade ago, the survey of 2,000 adults by One Poll showed.
Almost two-fifths (38%) said they did not feel fit enough to join a gym and 28% thought running was for those who are already fit and healthy.
The BHF called the figures "worrying", warning heart and circulatory disease affects around seven million people in the UK and is responsible for around 155,000 deaths each year - an average of one person every three minutes.
The charity has launched a new fundraising campaign called MyMarathon, which urges the public to run the marathon distance of 26.2 miles over the course of a month.
Christopher Allen, senior cardiac nurse at the BHF, said: "These statistics are concerning, and paint a worrying picture about the nation's fitness levels.
"Heart disease can affect anyone at any age, but keeping physically active is one of the best ways to help build a strong and healthy heart so we shouldn't ignore the benefits.
"Running a marathon is no easy feat, but with the MyMarathon challenge you decide the place and the pace, so it's a great way for people of all fitness levels to get active and help support our vital research. Now everyone can say they've run a marathon this May!"
Funds raised by the challenge, which starts in May, will go towards research, the charity said. To sign up, visit www.bhf.org.uk/mymarathon.