MELBOURNE, Australia—Breaking a sweat while exercising at least once a week for around 20 minutes may stave off the development of knee osteoarthritis (OA), according to a new report in the October 15 issue of Arthritis Care & Research.¹
"Both intensity and duration of physical activity were significant, but the amount of physical activity required for joint health remains unclear. Our data suggest that at least 20 minutes once per week of activity to result in sweating or some shortness of breath might be adequate," write researchers led by Tina L. Racunica, BPHARM, MBBS, of Monash University, Alfred Hospital in Melbourne, Australia.

The new study comprised 257 healthy adults between the ages of 50 and 79 with no history of knee injury or OA who were recruited from the Melbourne collaborative cohort study. All subjects underwent magnetic resonance imaging (MRI) exams on the tibia bone and tibiofemoral joint of their dominant knee. Study subjects also answered questions regarding their exercise and walking habits as well as their routine activity at home and work. Researchers used data on weight, height, body mass index, and physical activity from questionnaires completed between 1990 and 1994 to serve as the baseline.  

Vigorous activity boosts tibial cartilage volume

Both baseline and current levels of vigorous physical activity were associated with an increase in tibial cartilage volume that was free from cartilage defects. Moreover, tibial cartilage volume increased with frequency (P = .01) and duration (P = .001) of vigorous activity. Recent weight-bearing exercise was also linked to increased tibial cartilage volume (P = .02) and reduced cartilage defects (P = .02), the study showed. Moderate physical activity, including walking, was associated with a lower incidence of bone marrow lesions in the new study (P = .04). 

"These results suggest a beneficial effect of vigorous physical activity on tibial cartilage," the researchers write. "In the subgroup of subjects who undertook less vigorous physical activity, although there was no evidence for a direct effect on cartilage, a possible beneficial effect of walking on reduced risk of bone marrow lesions was demonstrated."

No evidence that more cartilage volume protects against OA

The new study "suggests that in persons without OA, cartilage volume increases in those exercising more," said David Felson, MD, professor of medicine and epidemiology and chief of the clinical epidemiology unit at Boston University School of Medicine in Massachusetts.

"This may represent the trophic effect of exercise on cartilage and it may be healthy although there is no evidence that more cartilage volume protects in anyway from OA," he said. Still "this does suggest that physical activity's effect on weight-bearing joints can be detected and in normal knees, may be healthy," Dr. Felson concluded.

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