Moderate Exercisers Have Strikingly Lower Knee Osteoarthritis Risks

Badley E. Editorial: Inactivity, disability, and death are all interlinked. British Medical Journal (2014) doi: http://dx.doi.org/10.1136/bmj.g2804 (Published online April 29, 2014)

Dunlop DD, Song J, Semanik PA, et al. Research: Relation of physical activity time to incident disability in community dwelling adults with or at risk of knee arthritis: prospective cohort study. British Medical Journal (2014) doi: http://dx.doi.org/10.1136/bmj.g2472 (Published online April 29, 2014)

Cooper R, Strand BH, Hardy R, et al.Research: Physical capability in mid-life and survival over 13 years of follow-up: British birth cohort study. British Medical Journal (2014)  doi: http://dx.doi.org/10.1136/bmj.g2219 (Published online April 29, 2014)

Even a small increase in the duration of light physical activity may reduce the incidence of knee osteoarthritis (KOA) in adults with risk factors for KOA. It may also reduce the progression of KOA in adults who already have KOA.

An editorial noted that about an hour a day “might do the trick” – and people who watch a lot of television might do this by moving around during commercials. In round numbers, people who spent four hours rather than three hours on light activity had a one-third lower incidence of disability.

The significant word is “might.” Randomized controlled trials have shown that physical activity reduces disability. The authors note that this is an observational study, and association does not mean causation. However, they tried to correct for confounding factors in several ways, such as controlling for baseline gait speed.

The study by Dunlop and colleagues followed 1,814 participants with or at risk of KOA in four US cities for two years. The primary outcome was incident disability. The secondary outcome was progression to a more severe level of disability. They assessed the physical activity of each patient at baseline by seven-day monitoring with an accelerometer that measured minutes spent on activity that was sedentary or of light or moderate to vigorous intensity. Increasing time was associated with better outcomes, but the most striking difference was that between the lowest and second-lowest quartile of time spent on light activity.  

Among subjects in the most sedentary quartile, almost 15% developed disability over two years.

In the British birth cohort study, physical capability at age 53 predicted survival 13 years later. Those who scored in the lowest quintile on a three-part test had a death rate four times higher than those in the highest quintile. Those who were unable to perform any of the three parts had a death rate eight times higher.

Cooper and colleagues followed a cohort of 5,362 March 1946 births  from the Medical Research Council National Survey of Health and Development. In 1999, 2,984 were assessed with home visits by a trained nurse. This is a younger population than iin previous studies.

Physical capability was measured by grip strength, chair rise speed, and standing balance time. Participants were divided into five groups by performance, on each test and in a composite of three tests, and into a separate group for those who were unable to do the tests at all.

In the main sample of 2.984 participants, physical capability scores were associated with cardiovascular disease, diabetes, and severe respiratory symptoms (as well as witih socioeconomic position and generally healthy lifestyles). Deaths from cancer (n=88) and cardiovascular disease (n=47) were more common than from all other causes (n=42) between ages 53 and 66.

The authors conclude that these simple, inexpensive tests can identify vulnerable target groups for intervention – although whether interventions improve survival rates requires further research. In the US, the Lifestyle Interventions and Independence for Elders Study is examining the impact of physical activity.