Walking can help protect people who have osteoarthritis, or are at risk of developing the condition, from functional limitation, such as difficulty walking up stairs or getting up, the study found.
Researchers said it was an inexpensive intervention that could avoid the disabling effects of mobility problems within just a few years.
The team from Boston University in Massachusetts measured daily step counts for 1,788 patients with or at risk of knee osteoarthritis taking part in the Multicenter Osteoarthritis Study.
Patients used a monitor for a week to log their steps. Researchers compared these to levels of functional limitation in patients two years later.
They found that each additional 1,000 steps walked per day was associated with a 16-18% reduction in functional limitation. Analysis showed 6,000 steps a day was needed to protect most people against mobility problems.
Study lead Dr Daniel White from Boston University said: 'Walking is an inexpensive activity and despite the common popular goal of walking 10,000 steps per day, our study finds only 6,000 steps are necessary to realise benefits.
'We encourage those with or at risk of knee osteoarthritis to walk at least 3,000 or more steps each day, and ultimately progress to 6,000 steps daily to minimise the risk of developing difficulty with mobility.'