Continuous physical activity and the incidence of degenerative changes occurring in the lower limbs

In order to evaluate the impact of physical activity, especially continuous activity such as walking, cycling or running, on the lower limb joints, we overviewed approximately one hundred sources observing the subject from various directions and from different research points of view. The sources were divided into five categories: those claiming damage, those that are inconclusive, those claiming no damage, reviews, and animal experiments. Reviewing this comprehensive material revealed the evidence that high impact sports activity will damage a normal joint which has not suffered a previous injury or anatomic variation and which does not carry a genetic fault, to be borderline, though existent. In many of the cases which do suffer damage, a concealed injury has previously occurred, single or recurrent, and the injured joint would tend to present with secondary arthritic changes. The evidence that continuous non-high impact physical activity like walking, cycling or running would damage a joint with no prior anatomical damage and which does not suffer a biomechanical or genetic fault, is weak and non-persuasive, while the literature supporting no damaging effect or even improvement of the joint construction is far more persuasive and abundant. This evidence is stronger in animal experiments than in research performed with human subjects. The safest activity, it seems, is gradual and graded activity with no exploding force, not extreme and which is not irregular for the individual trainee. The advantages of the physical activity to the general health as well as to the musculo-skeletal system seem to strongly overcome their potential risks.