Your leg size may predict your risk of knee osteoarthritis

If you’re a runner, your well meaning, non-running friends have probably told you more times than you can countthat your sport is hard on your knees. While a growing body of research shows that running actually strengthens our joints, a recent study suggests that runners with lower levels of lower-limb muscle (i.e., skinnier legs) are more likely to suffer osteoarthritis related to their activities.

The study

Researchers out of the Erasmus Medical Centre in Denmark analyzed the data from an earlier project, The Rotterdam Study, looking for information on the impact of weight-bearing activities on the risk of knee osteoarthritis (OA). They discovered a significant association between engaging in activities such as walking, running and weight-bearing sports and an increased likelihood of developing OA; but this link was only pronounced in individuals with lower levels of lower-limb muscle mass–i.e., people with skinnier legs.

Should female runners lift heavy weights?

The study used DXA scans (an imaging test used to measure bone density and body composition) to assess the lower-limb muscle mass of more than 5,000 participants, and then divided them into three groups, according to the results. During the following six years, 8.4 per cent of the 5,003 participants developed new-onset knee OA. Individuals who reported regular participation in weight-bearing activities, and who were also in the subgroup of having the lowest third of lower-limb muscle mass, had as much as 50 per cent increased risk of developing knee OA. Participants in the middle and upper rankings for lower-limb muscle mass showed no relationship between their level of exercise and knee OA risk.

The study found that non-weight-bearing exercises like swimming or cycling showed no correlation with knee OA risk. This suggests that how physical activity impacts joint health may vary depending on the type of exercise performed. Lead researcher Joyce B.J.van Meurs emphasizes the need for caution, especially among individuals with low muscle mass engaging in weight-bearing activities.

But doesn’t running make our joints stronger?

This study contrasts some of the leading research about joint health and the importance of weight-bearing activities as athletes age. The researchers acknowledge that past studies looking for a connection between impact-bearing activities and knee OA have failed to show any association. A recent, large meta-analysis found “no association of total physical activity with increased risk for knee osteoarthritis.”

While shedding light on the intricate relationship between physical activity and knee OA risk, the study acknowledges its limitations, and further research, including larger sample sizes and diverse methodologies such as randomized clinical trials, is essential to validate these findings and provide more definitive insights.