Knee discomfort after forty does not automatically mean you should stop moving. Joints often respond well to regular activity when the amount, speed and difficulty are matched to your current strength, symptoms and recovery capacity.
Useful rehabilitation commonly builds strength around the hips, thighs and calves while improving balance and control. Begin with a manageable level, monitor how the knee responds later that day and progress gradually instead of making sudden large increases.
Recovery also benefits from consistent sleep, comfortable daily movement and sensible breaks between demanding sessions. Sharp pain, major swelling, locking or repeated giving-way deserves an individual assessment before you continue exercising.