Exactly why Exercise?
P90X WorkOut

If you have a knee injury, you may worry that exercising might lead to more damage or pain. But the opposite is true: Strengthening your muscles that support your knee, and keeping them flexible, is the best way to prevent further injuries. Start slowly, and build your strength with time. Some muscle soreness is normal if you exercise. But you shouldn’t experience more pain, especially in your own knee. If you do, stop and contact your medical professional.

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