Concerns were raised by almost two-thirds of 2,000 adults surveyed by the Chartered Society of Physiotherapy (CSP), which is encouraging people to take more physical exercise.
Hundreds of physiotherapists will visit workplaces to urge employers to help their staff lead healthier lives.
The poll also showed that most adults were worried about having to work later in life so they can have enough money in their retirement.
Almost a third of 18 to 24-year-olds believed they would have to work into their 70s before they can retire and draw a pension.
Seven out of 10 people surveyed admitted they were exercising for less than the two-and-a-half hours a week recommended by medical officers.
CSP said its study showed that not enough employers were looking after the wellbeing of their staff, with fewer than one in five adults surveyed saying their boss encouraged them to take proper breaks, or even annual leave.
Phil Gray, chief executive of the CSP, said: "We completely understand the fears people have about working longer.
"Clearly these are tough times for employers, but it's in everyone's interest for staff to be healthy and productive. Research shows that looking after your workforce actually saves money so it is important that employers recognise these benefits."