Our kneecap will grind against the sides of the groove that it moves through and pain, swelling, and trips to our favorite physical therapist will follow. This can happen around any joint in the body including elbows, shoulders, and the joints in the lower back. Often times having weak abdominal muscles and a tight lower back are the culprits for low back injury. This is the same idea. A loss of balance is bad.
Balance is achieved in our body by cross-training.
This is where we do at least two types of exercise regularly that work opposing muscle groups. Cross-training is not ideal for competitive athletes in midseason trying to do their best in one specific event. If you want to run fast, you need to run a lot. But cross-training is great for people trying to maintain a healthy body. Walking or running and cycling are great complements to each other because they maintain balance around the knee.