Run while you're young

Rather than extrapolate data from ex vivo and animal studies, researchers can use MR imaging directly on humans to measure T2 changes in knee cartilage caused by running, according to a study presented at the International Society for Magnetic Resonance in Medicine meeting in Japan.

Healthy collagen, which has a short T2 relaxation time, is a highly organized, anisotropic structure that restricts the flow of water. The resulting cushion of water is used by the body to absorb shock. Running compresses the cartilage, disrupting its anisotropic structure and lengthening its T2. Severely damaged collagen allows water to flow freely, thereby destroying its shock-absorbing properties.

Dr. Timothy J. Mosher, chief of musculoskeletal imaging, MRI, and radiology research at Penn State University, and colleagues obtained quantitative T2 maps of the femoral tibial joint of trained marathon runners. They found a decrease in T2 in the outer 70% of cartilage of the older runners. This could not be attributed to a loss of anisotropy because the T2 would have increased. They theorized that the long-term effects of age and running may have caused preclinical damage to the collagen matrix, allowing water to move freely. Mosher had previously demonstrated age-related collagen damage over time (Radiology 2000;214:259-266).

"We all need weight-bearing exercise, but it might be prudent for some of us as we age to include more swimming and less running, to reduce the stress on cartilage," he said.