Do you lock your knees when standing or while doing certain movements like squats or standing up from a chair? Do you even notice you are doing it? Most people have found themselves “locking their knees” at some point. But what does it mean, why do we do it, and is it bad for your knees? Let’s discuss that.
What does “locking your knees” mean?
When you lock your knees, you completely straighten them all the way until the knee joint is full straight or extended. You knee joint pushes backwards and you may even notice your weight shifts backwards as well. Now, what happens when you are in this “locked knee” position is the muscles aren’t supporting your knee, only your ligaments and the bone itself.
Some common times people lock their knees:
- When standing in line for a long time
- When doing certain movements such as squats, standing up or leg presses at the gym
- When doing a stretch like a hamstring stretch in standing where you touch your toes
- When leaning your back against a wall
- When walking long distances
Locking your knees is only done when you are in the weight bearing position since it is a compensation.
Why do we lock our knees?
Most of the time we lock our knees when our leg muscles are tired. If you are waiting in line or standing for a long period of time, you may get less leg fatigue when locking your knees. You may not even notice you are locking your knees either. You also may be more predisposed to stand in this position (or even walk) due to your anatomy. Individuals with a significant forward tilt of the pelvis are more likely to lock their knees when walking or standing.
Is locking the knees good or bad for our knees?
Typically, you want to avoid this position as often as possible. Locking the knees can put a lot of pressure on the posterior (back) knee joint capsule, posterior ligaments and the hamstring tendons. When you push your knee back when locking them, there is a lot of extra pressure on those structures in the back of the knee. They are stretching more than they are supposed to, which can lead to irritation and/or damage.
Locking the knees can also disengage the quad muscles. When we completely extend or straighten our knees, the quad muscles turn off. This can be a good thing if we don’t push the knee all the way back into that “locked” position. Allowing the quads to rest when the knee is straight (but not locked) it’s important for standing endurance. This is actually how we, as humans, have developed the ability to stand on 2 feet for a long time.
In some cases, locking the knees can reduce circulation and cause some people to faint or pass out. This is rare, but we’ve all heard of those stories where someone is at the alter and falls over. Could that be from locking the knees? Possibly! The pressure of the knee in that hyperextended position can compress the poplieteal vein in the back of the knee. This vein is responsible for returning blood back to the heart. It is a very big vein that contains a lot of blood. The lack of movement due to locking the knees can also allow blood to pool in the lower leg reducing blood flow back to the heart, which ultimately gets back to our brain. The calf is a very large muscle that helps pump blood back to our heart. We call the calf “the second heart of the body”. If you ever find yourself feeling faint in the standing position, try some heel raises to help move blood back to your brain.
Alternatives to locking the knees
If you need to stand for a long period of time, try to be cognizant of your knees positioning. If you notice your knee is pushing into that hyperextended position, slightly bend the knee and create a “soft knee” position. This will allow the tissues in the back of the knee to not become overstretched and allow the quad muscle to do what it is designed to do. You may find your leg gets tired when you get into a “soft knee” position. If this is the case, you can alternate between locked knee and soft knee position until you can build enough tolerance to standing correctly.
Is locking the knee bad if you’ve had a knee replacement?
The same principles will apply for those who have and have not had a knee replacement. When you lock the knee with a knee replacement, you still put extra pressure and over stretch the posterior (back) tissues of the knee. Some people after a knee replacement cannot hyperextend or lock the knee because the implant was placed in the knee to avoid this positioning. This means your quad muscles have to be very strong to hold up your weight when in standing. This is a common issue after a knee replacements since the quads are immediately weakened due to the traumatic nature of the surgery, swelling in the knee and due to pain.
If you notice you do lock your knees and you have a knee replacement, focus on strengthening your quads as much as possible to avoid any posterior tissue irritation.
Quad exercises:
Level 1: Quad Sets - lay on your back and place a rolled up towel under the back of your knee. The knee will rest into a bent position. Next, lift the foot off of the ground under the knee is straight. Slowly lower foot back to ground.
Level 2: Straight Leg Raise - lay on your back, bend your non surgical leg. Lift your surgical leg up towards the ceiling with the toe pointed up.
Level 3: Stand Up Sit Down - sit at the edge of a chair, stand up to full standing position with knees straight (but do not fully lock the knees) then sit back down slowly.
Are you at least 2 months post surgery and want to work on your quad strength? Join the 4 Week Strength Class taught by Dr. Samantha Smith and knee replacement physical therapist.
