6 Knee Strengthening Exercises to Prevent Injury

Knee injuries are among the more common injuries sustained from sports and recreational activities. Even though many knee injuries are caused by internal issues (inside the knee), strengthening the muscles on the outside of the knee can prevent injury and enhance healing. In this article, we discuss six ways to strengthen the knee and other muscles to enhance knee stabilization.

Structures of the knee

The image above shows the outer and inner structures of the knee, including the bones, ligaments, muscles, tendons, and cartilage (menisci).

Muscles that stabilize the knee

First, the main muscles supporting the knee are the quadriceps (quads), a group of four muscles in front of the thigh. The name quadriceps comes from the Latin word "quad," which means four.

Second, several muscles assist in stabilizing the knee, including the hamstring muscles (back of the upper leg), calf muscles (back of the lower leg), hip muscles, and the buttocks' gluteal muscles.

Finally, having strong core muscles, including the abdominals, can help stabilize the knee. One study published in 2015 in the Journal of Athletic Training found that strengthening the core and hips was as effective as strengthening the knee in treating a knee condition called patellofemoral pain syndrome.

Knee strengthening exercises

Experts recommend doing 2–3 sets of 10 repetitions for the following exercises. In addition, as with any physical activity, it’s best to stretch before and after these strengthening exercises.

Leg extensions

Leg extensions are simple exercises that can be done either on a gym machine or at home sitting in a chair. For increased training, weights can be added to the gym machines and resistance bands at home.

1. Sit with the back straight
2. Extend the legs until straight
3. Hold for a few seconds
4. Bring legs down to the starting position

Squats

Notice the person in the image above is holding their arms extended straight out to maintain balance — this is a personal preference. Holding onto a chair or stationary object also helps with balance, even with extended arms.

1. Stand with legs shoulder length apart and feet slightly pointed outwards
2. Move from standing to squatting position by bending the knees
3. Squat down until the buttocks are approximately 1–3 feet from the floor
4. Extend arms straight out for additional balance
5. Return back to the standing position

Squats help strengthen the quadriceps, hips, and abdominal muscles.

Half squats

Some people cannot tolerate or perform a full squat correctly due to the pressure it places on the quadriceps and knees, so performing a half squat is a more acceptable alternative. Half squats can also be performed while holding a chair, as shown in the image above. Notice how the person does not go as deep down as in a full squat, shown above.

1. Stand with legs shoulder length apart (and holding onto a chair)
2. Bend the knees, but only bend half way
3. Return to the starting position by standing straight

Hamstring curls

Hamstring curls have many variations, including without weights and standing. The person in the image is lying on a table, but hamstring curls can also be done lying flat on the floor.

1. Lay face down on a flat surface with a dumbbell between the feet
2. Bend the knees and curl them up to 90 degrees
3. Return the legs to the straight position

Hamstring curls strengthen the hamstrings, calf, and gluteal muscles.

Calf raises

Calf raises are ideal exercises for strengthening the calf muscles. The illustration shows a person performing calf raises while holding onto the back of the chair. A chair isn't needed for calf raises, but holding onto a fixed object for balance helps with stability.

1. Stand with feet flat
2. Lift the heel to stand on the toes
3. Hold for a few seconds
4. Return to the starting position

Calf raises can also be done sitting. Adding weights to the thigh increases resistance, following the same directions as for the standing calf raises.

Abdominal strengthening exercises

There are many abdominal strengthening exercises. However crunches are one of the best.

Straight crunch

A straight crunch is shown above. However, there are numerous alternatives to this exercise, including crunching sideways and moving the legs. One important aspect of doing a crunch is to avoid putting too much pressure on the neck or spine.

1. Lay with the back flat, knees bent, and feet flat on the floor
2. With hands behind the head, contract the abdominal muscles to bring the shoulders upwards (make sure to exhale while contracting the abdominals)
3. Hold for 2–3 seconds
4. Return to a flat lying position

Why isn't running enough to strengthen knee-stabilizing muscles?

Even though running uses several muscles and improves muscle tone in the lower extremities, buttocks, hips, and abdominals, there is no conclusive evidence of significant muscle strengthening (from running) to prevent knee injuries.

In other words, to strengthen the muscles that stabilize the knee and prevent knee injury, resistance training must be incorporated into an exercise program — running is not enough.

To stabilize the knee and prevent knee injuries, performing strengthening exercises of the lower extremities, core, and buttocks is needed.