How many steps per day protects against knee OA?

Moderate levels of walking prevent development and progression of knee OA – but not the 10,000 steps a day threshold often recommended as the minimum daily ‘dose’ of activity, Tasmanian researchers have found.

Walking between 7500-10,000 steps per day appears to be the ‘sweet spot’ for preventing progression of OA, according to one of the first studies to use objective measures of physical activity (pedometers) and knee OA (MRI-detected osteophytes).

After following up 408 adults aged 51-81 for an average of 2.7 years, the researchers from the Menzies Institute for Medical Research, Hobart, found that being moderately active was protective against an increase in MRI-detected osteophytes. However the findings were only significant for women, people with radiographic OA, obese people and those who with a history of knee injury.

MRI evaluation of knee osteophytes was used as a marker of OA because osteophytes are a fundamental sign of disease progression, having previously been shown to be predictors of cartilage defects, bone marrow lesions and knee pain scores.

Among participants in the study, being moderately active (7500-10,000 steps per day) was associated with a significant protective effect against increases in MRI-detected osteophytes in females, with a relative risk (RR) of 0.42 compared to being less active (<7500 steps per day). Similarly, being moderately active was protective against osteophyte increases for obese subjects (RR 0.50), those with radiographic OA (RR 0.68) and those with a history of knee injury (RR 0.27).

Being highly active (more than 10,000 steps per day) was neither protective nor deleterious towards increases in osteophytes in any patient group. The researchers noted that previous studies had shown detrimental effects on OA knee changes from walking more than 10,000 steps a day.

“So far, there is no guideline on the amount of physical activity required to prevent OA progression, and it is still uncertain what level of [walking] should be promoted to individuals with certain knee OA risk factors,” they wrote in the journal Osteoarthritis and Cartilage.

The lack of a protective effect of walking against OA progression in males might be related to gender differences in knee loading, the researchers postulated.

“These findings would be clinically relevant, and clinical practitioners could encourage moderate [ambulatory activity] particularly among OA susceptible groups such as women, obese people and those who had knee injury history and radiographic OA,” they concluded.

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