physical activity decreases knee arthritis disability

bmj article found that there was a relationship between greater physical activity and reduced risk of disability in adults with either known DJD or at high risk (see physical activity dec knee arth bmj 2014 in dropbox, or doi: 10.1136/bmj.g2472). prospective multisite cohort study of 1680 community dwelling adults aged >49yo with known knee DJD (symptoms in at least one knee with osteophyte and pain, aching or stiffness on most days for at least one month in the prior 12 months) or risk factors for developing DJD (knee symptoms in the prior 12 months, overwt, knee injury causing difficulty walking for at least one week, fam hx of total knee replacemetn for DJD, Heberden's nodes and age 70-79). primary outcome of development of disability (defined as difficulty in carrying out activities essential to independent living) at 2 year followup in those free of baseline disability. also followed a cohort of 1814 adults to assess disability progression as a secondary outcome (this group was free of severe baseline disability in basic activities of daily life). this study assessed the intensity of physical activity (moderate-vigorous vs light intensity), using an accelerometer for 7 consecutive days (which measures the weighted sum of accelerations over one minute, weighted by the magnitude of acceleration) to verify. the patients were stratified into quartiles of either light or moderate-vigorous activity. results:

    --149 cases of new disability identified, 

    --these 149 people averaged 302 minutes/day of non-sedentary activity, 284 minutes being light intensity activities (ie, not a lot of moderate-vigorous activity)

    --primary outcome: light intensity activity had strong inverse relation with development of disability for men, women, and adults with or without baseline knee DJD. similar strong inverse relation with moderate-vigorous exercise, but of note the benefit of light intensity activity was independent of doing more vigorous activity

    --as an example of the protection: average person in 2nd quartile of light activity (mean 255 min/d) had 43% decrease in age-adjusted hazard for developing disability (vs patient in quartile with least time, at 192 min/d). and, average person in 2nd quartile of mod-vigorous activity (18 min/d) had 53% reduced risk of developing disability as those in lowest quartile (12 min/d).

    --secondary outcome: greatest disability progression in those who spent the least time in light or moderate-vigorous activity

this was an observational study. concern is always that of reverse causation (eg, unmeasured baseline disability which decreased the likelihood a person would exercise and itself increased likelihood of defined disability later). to minimize this possibility, they did start with patients who were free of disability at baseline and controlled for baseline gait speed as well as potential confounders of chronic medial conditions, socioeconomic factors, obesity, depression, pain. (turns out that depression and pain were independently assoc with developing disability).  this study adds to prior studies (including RCTs) also finding that exercise reduces disability. these results, perhaps not so surprising, reinforce that even light physical activity appears to protect against disability. similar to small amounts of weight loss (5% range) is associated with pretty striking effects on insulin sensitivity and diabetes control.  bottom line, i think, is that we as medical providers can advocate for small incremental changes with patients, and that these are actually very helpful -- patients do not need to run marathons or revert to their ideal body weight to get significant benefit of lifestyle changes.