Most of the tissues in the human body respond to the demands placed on them. For example, the weightlessness of space travel weakens soft tissues. Lifting weights improves muscle tone. Walking and other weight-bearing exercise can improve bone strength. But cartilage in the knees of triathletes doesn’t seem to get thicker from their heavy schedules of training and competition.
This was an unexpected finding in a recent study that compared the knee joint cartilage of nine triathletes and nine inactive volunteers. To be included in the study, the triathletes had to have been active throughout life and training for at least 10 hours per week over the past three years. The inactive group included people who had never done more than one hour per week of any type of sport or heavy work at any time in life.
Using magnetic resonance imaging (MRI) and three-dimensional imaging technology, the authors calculated cartilage thickness of the right knee joint of each participant. In general, the results showed wide differences in the cartilage thickness between participants. Although there were parts of the knee that tended to have slightly more cartilage in triathletes, there were some areas that had less. The conclusion drawn by the authors is that the cartilage was generally not thicker in the knee joints of triathletes. “These results are unexpected,” say the authors, “in view of the functional adaptation observed in other musculoskeletal tissues.”
Past animal studies that measured the effect of activity on cartilage have shown varied results. No other studies have been done measuring the effect of physical activity on cartilage thickness in the human knee. Even though the cartilage didn’t look thicker on MRI, the authors caution that these types of images don’t show whether the chemical makeup is different, since MRI can’t detect these kinds of changes.