What In Vitro and Animal Studies Show About Loading and Cartilage

Cartilage has no blood vessels, so it relies on mechanical loading to stay healthy. In vitro studies apply load to samples of cartilage in a machine. The process is summarized in three steps: load is applied, chondrocytes begin to communicate, and a cellular response follows. Very high loads and unloading both trigger a catabolic response with inflammation and aggrecan loss, while moderate loading between these extremes appears beneficial. Alessio then presents his systematic review of exercise in healthy animals, comparing low, moderate and high doses with non-exercising controls on aggrecan, collagen and cartilage thickness. High doses reached up to a marathon a day for a year. Low-dose results were mixed and inconclusive. No moderate-dose study showed harm, and some showed benefit. Most high-dose studies showed loss of aggrecan, collagen and thickness. The conclusion is a nonlinear dose-response relationship. He adds that early laboratory and animal findings were applied directly to patients, which helped create the belief that exercise damages the knee, and that human evidence is needed first.