From the point of view of one’s physical quality, knee pain has not only a lot to do with the strength, flexibility and stability of a climber’s knees, but also his body structure and posture.  For example, people who are born with X-shaped or O-shaped legs or are severely duck-footed will experience knee strain during climbing.  In addition, some climbers are overweight, too old, have poor health, or suffer from old injuries, and all these factors can also cause knee injury.  As one grows older, his physical strength, endurance and flexibility decreases, while the potential for knee injury increases.  People who have a history of injuries are more likely to be re-injured than those who do not.