You’re in a yoga class and you’ve just arrived into your warrior II pose. Your body is feeling strong, your core is engaged, your gaze is steady, and then the yoga teacher says to you: “Make sure your front knee never moves forward past your ankle.”
You panic! You look down at your knee. It’s an inch in front of your ankle. You pull it back slightly, even though the posture now doesn’t feel quite as natural in your body. In your mind you hope to yourself that you haven’t done any damage to your knee in those brief moments.
If you’ve been practicing yoga with a teacher odds are you’ve heard this cue.
However, if you look at the anatomy behind this direction it’s actually a bit misleading.
So let’s explore this cue and understand what’s really being said when a teacher tells you not to "move your knee past your ankle."
To understand where it stems from, what’s really happening in your knees during these postures and what the risk is, we need to dive deeper into the world of biomechanics.
What’s with the cue “don’t let your knees move past your ankle?”
This is one of the most commonly-said and misleading cues in the yoga world. For one reason or another, the yoga community has taken to saying it all over the place–from your crescent lunge, to your warrior II, to chair pose.
Take a moment to imagine yourself walking up the stairs. Think about your knees. Where are they in relation to your ankle? That’s right! They extend in front of the ankle! In fact, you’d have a very hard time walking up or down stairs if you were preventing your knee from moving forward.
So where did this cue come from? One theory is a 2003 study from Fry, et al that examined torque in the knee and hip joints during squatting.
The study examined torque when the knees were allowed to move freely forward (unrestricted), such as in image A, and when the knees were restricted, as shown in image B. This study found that when the knee moved forward unrestricted, the knee torque was: 150.1 and the hip torque was 280.2. When the knee was restricted, the knee torque went down to 117.3 and the hip torque raised to 302.7.
Wowza!
Wait a minute, what does torque mean?
In the simplest terms, torque is defined as a twisting force. However, to go into a deeper level of explanation, this passage from Whitney Lowe, LMT is helpful:
“There is [a] type of motion in the body called rotary motion. Rotary motion occurs when a force is applied to one section of an object, and another section (such as the other end) remains fixed. In the body, this happens when a muscle pulls on one end of the bone and the other end is fixed (held still). The result is movement of the non-fixed end. For example, when the proximal end of the hamstring muscles are held stationary at the pelvis and the distal end pull on the tibia and fibula, there is rotary motion at the knee joint (flexion). Torque is a force that is produced by rotary motion.“
Torque is a necessary part of human movement. However, when there is a threshold level of force that each joint can safely absorb. If there’s too much torque in your joints, you risk injury.
Back to the knees...
In the conclusion from the Fry study, they state: “Although restricting forward movement of the knees may minimize stress on the knees, it is likely that forces are inappropriately transferred to the hips and low-back region. Thus, appropriate joint loading during this exercise may require the knees to move slightly past the toes.”
In conclusion, while pushing your knees further than your ankle may result in more force on the knee joint, it is not a force that the knee can’t handle. Furthermore, the result of stacking your knee directly over your ankle increases force in your hip, which may be more problematic for some.
Overall, it’s not likely to cause injury if your knee moves past your ankle in bent-leg poses.
Fun thought: Other potential origins.
While writing this post, I had to stop and think about why this cue became so pervasive. Well, one theory is that the cue morphed into “don’t let the knee move past your ankle” from the original cue of “keep your knee stacked directly over your ankle.”
This second cue has a lot of validity to it. The concept of keeping your knee stacked over your ankle invites the practitioner to ensure their knee isn’t splaying inward or outward. This splaying, in fact, can be problematic for the knee joint.
But back to the matter at hand...
Ultimately, what we’ve learned through newer studies in the field of biomechanics is that the cue: “never let your knees move past your ankle” can be confusing. The adjustment to make is a mental one. Keeping your knee stacked directly over your ankle is a safe place for the knee to be, but if your knee moves beyond, that's okay, too. The further you push your knee forward, the more force in the knee joint. But your knee joint can handle it, as long as the knee is not splaying inward or outwards. (But we’ll get to that in another post.)
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