Your knee is the largest joint in your body and is very vulnerable to injuries. As a result, the structures that support the joint — the muscles, ligaments and tendons — can become weak and loose, making your knee unstable. Sports injuries or accidents aren't the only causes of knee instability. Lack of exercise and some health conditions such as arthritis can also be contributing factors. Strengthening exercises build muscle that supports the knees and strengthens the ligaments and tendons to increase stability.
These isometric exercises allow you to strengthen the quadriceps muscle at the front of the thigh without placing weight on your knee or requiring too much movement of the joint. Begin by sitting down with the leg of your affected knee outstretched in front of you. Keep your other leg bent. Slowly contract your quadriceps muscle as much as you can. The exercise will pull your kneecap upward. Hold for 5 to 10 seconds, then relax. Repeat 8 to 12 times, then switch legs. If you find it more comfortable, you can place a rolled towel under your knee.
The squat is a common knee rehabilitation exercise — and it's also versatile. For instance, you can do it against a wall or without support, or you can do it with one or both legs on the ground. If you're just starting to strengthen your knee, try the wall squat. Stand up and lean back against a wall with your feet about two feet away from the wall. Slowly lower yourself into a squat. Don't let your knees bend beyond 90 degrees or protrude over your toes. Hold for 5 to 10 seconds.
Prone Hamstring Curls
You can perform hamstring curls standing, but you might find them easier to do while lying on your abdomen. Fold your arms and rest your head on them. Begin with both legs outstretched. Slowly curl your right leg toward your buttocks until your knee reaches about 90 degrees — no further. Hold the contraction for three to five seconds, then lower your leg. Repeat 8 to 12 times, then switch legs.
Always warm up before performing strengthening exercises for your knee. For instance, walk or bicycle at a leisurely pace for 5 to 10 minutes. Perform each exercise in a slow, controlled motion. Stop if you experience sharp, stabbing pain during any of the exercises. Do a few gentle stretches after your strengthening routine to relax the muscles and reduce soreness and your risk of further injury.