The vastus medialis is one of the four quadriceps muscles that span the front of your thighs. The muscle attaches to the top, front portion of the femur -- or thigh bone -- on top and to your knee via the quadriceps tendon on the bottom. Along with the other three quadriceps muscles, the vastus medialis extends your knee.

Strengthening the muscle, therefore, requires repeatedly extending your knees against external resistance as part of a well-designed weight-training program. Consult a personal trainer to develop a program that's tailored to your goals and needs.

Warm Up Before You Work Out

Complete a five- to 15-minute general warmup period by cycling, jogging, jumping rope or walking at a low intensity. Stand upright with your feet shoulder-width apart, then flex your left knee until you feel a gentle stretch through your quadriceps. Return to the starting position immediately and repeat with your right leg. Complete at least 10 repetitions with each leg.

Barbell Squats

Barbell squats are a compound exercise that activate all of the quad muscles, with special emphasis on the vastus medialis. Start with no weight if you're new to resistance training. This helps you hone form. After a couple of weeks, add in the barbell with a light weight. Gradually increase the weight over the course of a few weeks or months.

How To: Hold a barbell across your shoulders and upper back while standing erect with your feet slightly wider than your shoulders and your toes directed forward. Squat slowly, keeping your spine straight, until your thighs are parallel to the floor, then powerfully extend your hips and knees to return to the starting position. Perform three to six sets of no more than six repetitions.

Walking Lunges

Lunges are another compound exercise that work much of your lower body, with an emphasis on the quads -- and the vastus medialis.

How To: Hold dumbbells just outside your hips from a standing position with your feet about 6 inches apart. Step forward 2 to 3 feet with your left foot, then squat after your foot is secure on the floor. Stop when your left thigh is parallel to the floor, then powerfully stand up and step back to the starting position. Repeat with your right leg and continue alternating sides for eight to 12 repetitions. Complete three sets.

Leg Extensions

Leg extensions are one of the few ways to isolate the quadriceps. Make sure you keep your knees from locking during the exercise and use a load that's challenging, but not overwhelming, or you risk injury to the knee joint.

How To: Sit on a leg-extension weight machine with your lower legs hanging off the edge of the chair and your feet under the padded foot bar. Hold the handles on the sides of the seat to secure your body, then repeatedly extend your knees to lift the bar and let it back down slowly. Perform three sets of eight to 12 repetitions.

Putting It All Together

All three of these exercises create a workout that you can perform two or three times per week on nonconsecutive days. Increase the weight every two or three weeks as you increase the number of sets and decrease the number of repetitions for the squat and decrease the number of repetitions for the other two exercises.

Rest for two to three minutes between each set for the squat and one to two minutes for the lunge and leg-extension exercises. If you're using a heavy weight for you, have a spotter stand behind you when you perform the squat.