“Lock your knees!” was the firm directive from my Yoga teacher. I’d decided to attend class in a new style, to try something different from the smorgasbord of modern brands. I enjoy keeping an open mind, knowing that various styles can do the same asanas in just a little different way. There’s usually no real “right” or “wrong.” What works for some body types and Yoga traditions doesn't work for others.
Staying open to the newness and variety of modern Yoga can invigorate a practice that may feel stale, but it’s important to retain awareness of proper biomechanical technique within each exploration – even if that means not following the advice of a new teacher.
Locking the knee is unnecessary and potentially leads to injury in the long run.
What does it mean to lock your knees?
Locking the knee maximally extends and fixes it, transforming it into a mechanically rigid structure that maintains a straight leg. At maximal knee extension, there’s a medial rotation of the femur (the big thigh bone) on the tibia (the larger of the two lower leg bones). It’s the inherent features of the tibia that lead to the “locked” feeling. A concave up-slope on the anterior portion of the medial condyle brings the rolling medial femoral condyle to a skidding halt while at the same time the convex down-slope on the anterior part of the lateral tibial condyle allows the rolling of the lateral femoral condyle to continue further forwards, thus bringing about the medial rotation that “locks” the knee into a groove.
Some people fully extend their knees whenever they stand still – at least one leg or the other – to improve stability and take the work off of the major muscles.
What’s the danger if you lock your knees?
Locking the knee places one’s body weight onto the joint in such a way that it forces the joint slightly out of place. That puts damaging mechanical forces onto the joint cartilage – both the cartilage covering the ends of the long bones and that of the menisci. The long-term result is cartilage degeneration and arthritis.
The effect is magnified by placing the entire weight of the body onto one leg as in some Yoga asanas like Tree pose (Vrksasana).
Locking the knees while standing can also cause the pelvis to tilt forward which can stress the hip joints and disturb posture throughout the spine.
Is there a test for those at greatest risk?
Yes. Some of us (and that includes me) have a greater tendency towards a hyperextendable knee joint with subsequent development of the cascade of degeneration, pain, and arthritis with knee locking in standing positions. Hyperextension of the knee occurs when the tibia glides on the femur excessively so that the joint moves past 180 degrees of openness – past a straight line.
Test: Sit up straight in Staff pose (Dandasana). The knees should not be externally rotated and the feet should be relaxed with no flexion at the ankle joint. Contract the quadriceps muscles. If the heels rise up off the floor, then it’s likely you have hyperextending knee joints.
What can you do to keep from locking your knees?
Maintain awareness – all the time. That means when standing in line at the grocery store and stirring the soup on the stove as well as when on the mat. For some, locking the knees into hyperextension is a firmly ingrained habit, one that can be conquered with attention. I always try to do my best with this throughout the day, which is why I found it disconcerting that during class, when my mind is most aware of my posture, I was told to do what I know is not best for me.
When instructed to “lock the knee” during Yoga sessions, extend the knee but don’t push it into a locked position. Then contract the quadriceps, the thigh muscles. Contracting the intrinsic muscles of the foot can help a little, too. Some people may benefit from wearing a knee brace.
Over the long-term, work on strengthening the quadriceps with Chair pose (Utkatasana), keeping the thighs parallel to the floor for as long as possible with each attempt. This will help to stabilize the knee and to prevent long-term damage.
Bottom Line: It’s unwise to “lock” your knees when standing, especially when all the weight is upon one leg. While it may be particularly damaging for those of us with a tendency to hyperextend, locking the knee joint is not good for anyone, and it’s unnecessary in Yoga.
Kathleen Summers, MD, PhD, is a contributor to Prevent Yoga Injury. She is a board-certified internist specializing in natural, Yoga-based care. Dr. Summers is a graduate of Northwestern University Medical School in Chicago and holds a second doctorate in neuro-pharmacology from Southern Illinois University. Currently, she is an Adjunct Clinical Instructor at Southern Illinois University School of Medicine, and she is a member of the American College of Physicians, the American Society of Nutrition, and the International Association of Yoga Therapists.
During her frequent travels to India, Dr. Summers researches Yoga and its therapies. She enjoys uniting her two passions, Yoga and medicine, and is continually exploring Yoga's healing concepts and integrating them with modern, evidence-based care. Her primary Yoga influences have been the tantric styles of Sivananda and Agama. She holds a 500-hr Yoga teacher training certification. You can also follow Dr. Summers on Facebook and Twitter.