Healthy Joint Decisions

Charles Ratzlaff
Charles Ratzlaff

A UBC researcher examines the impact of life-long physical activity on osteoarthritis risk

Being a top athlete is tough on the body. The hip and knee joints often pay the biggest price, suffering damage and leaving athletes at a higher risk of osteoarthritis (OA). But the Olympic medal contenders warming up in Vancouver may not be the only ones putting their joints at risk. With the help of funding from the Canadian Institutes of Health Research (CIHR), University of British Columbia PhD candidate Charles Ratzlaff is trying to find out if moderate exercise can cause similar damage in not-so-elite athletes and non-athletes.

"Certain labour-intensive occupations, such as farming, have been linked with hip and knee OA for some time," says Ratzlaff. "We also know that some types of sports injuries, such as a torn anterior cruciate ligament (ACL), can dramatically increase a person's risk of knee OA. I want to know if there is a similar risk for people who engage in moderate amounts of physical activity, such as running, over long periods of time."

What is joint load?
Each step you take, each stair you climb places weight on the joints in your body. “Joint load” is the measurement that scientists use to quantify the amount of weight that a joint experiences when you move. Joint load varies depending on your body weight and the type of activity you are doing.

High-load activities
Squatting
Kneeling
Stair climbing
Jumping

Low-load activities
Swimming
Cycling

To answer this question, Ratzlaff and his colleagues conducted an in-depth survey of 4,600 Canadian adults to determine the type and amount of exercise they had engaged in over their lifetime. They also constructed an index of the amount of weight the hip and knee carry during different types of exercise – a measurement known as "joint load". Using the survey results and the index, the researchers are analyzing the data to see if people whose joints carry more weight during their lives have a higher risk of OA in their later years.

"Interestingly, we found that the people with the highest levels of hip OA are on opposite ends of the spectrum – so having a very high joint load or a very low joint load over your lifetime may increase your risk of developing OA," explains Ratzlaff. "This suggests that the best place to be is somewhere in the middle."

Ratzlaff and his team also found that, while women are less likely than men to participate in sports, their hip and knee joints experience higher joint loads over their lifetime because they engage in higher levels of household activity. While it hasn't been studied yet, this finding may help explain why women have higher rates of hip and knee OA. Active girls and women are also about 5 times more likely than men to experience ACL tears, another factor that could contribute to higher knee OA rates.

Based on the research team's findings, it appears that for most people, sports-related wear-and-tear on joints is much lower than occupation-related joint stress. So lacing up your sneakers and spending your free time running around the park is not likely to increase your risk of OA.

"Keep walking, keep running and stay active," says Ratzlaff. "Take care of any physical injuries right away. Those would be my recommendations to people who are concerned about their joints."