Older people who watch more than five hours of television a day and indulge in three or lesser hours of physical activity in a week were at more than three-fold higher risk of being unable to walk or having difficulty walking, researchers warned.
The findings showed that people who watched five or more hours of television per day had a 65 per cent greater risk of reporting a mobility disability, compared with those who watched television for less than two hours per day.
Television viewing in the evening may be especially detrimental to health because it is not broken up with short bouts of activity, compared with sitting during the day.
"Television viewing is a very potent risk factor for disability in older age," said lead author Loretta DiPietro from the George Washington University.
Younger people might be able to get away with sitting for long periods because they are physiologically more robust.
But after age 50, prolonged sitting, and especially prolonged television viewing, becomes particularly hazardous, DiPietro said.
"We've engineered physical activity out of our modern life with commuting, elevators, the internet, mobile phones and a lifestyle that often includes 14 hours of sitting per day," DiPietro said.
"Our findings suggest that older people who want to remain fit must ramp up their daily physical activity and reduce the amount of time they spend sitting," DiPietro added.
For the study, published in the Journal of Gerontology: Medical Sciences, the team analysed data which kept track of men and women aged 50 to 71 from six states and two metropolitan areas, nearly 30 per cent of the previously healthy participants reported a mobility disability-having difficulty walking or being unable to walk at all.
"To stay active and healthy as you age, move more and sit less -- throughout the day -- every day," DiPietro added.