There is a principle in Chen style Tai Chi that, once understood, makes every posture in the entire practice suddenly make sense. Not as a collection of separate movements to be memorized but as a single formula applied repeatedly in different configurations. Most practitioners practice for years without being told this principle explicitly. They develop a feel for it gradually through correction and repetition. But having it stated clearly and precisely from the beginning changes the speed and depth of development significantly.
The principle is the opposing knee spiral. And it is the same in every posture, every transition, every form, every Push Hands exchange, without exception.
Two Axes, Not One
Before explaining the knee spiral itself, I need to clarify something that confuses students when they first encounter this principle: weight distribution and the issue/settle cycle are two completely separate axes of movement. Conflating them produces confusion. Keeping them distinct makes the whole system legible.
Weight distribution describes where the body’s mass is carried between the two feet at any given moment. In a bow and arrow stance, weight is 70 percent on one side and 30 percent on the other. In horse stance, it is 50/50. These proportions describe which foot is weighted and by how much. They do not change based on whether power is being issued or stored. A 70/30 weight distribution during the issue of power remains 70/30 after the power is issued and the body settles. Weight distribution is its own thing.
The issue/settle cycle is something different. It describes what the knees, waist, and body are doing as power is generated and then released. This cycle happens within a given weight distribution, not because of a change in it. Understanding this distinction is the foundation for everything that follows.
The Three Stances and the One Formula
In Chen style Tai Chi practice there are three fundamental weight positions that appear across every posture in the form. Weight left at 70 percent, which we call left bow and arrow stance. Weight equal at 50/50, which we call horse stance. Weight right at 70 percent, which we call right bow and arrow stance.
Across these three positions, and across every transition between them, the knee spiral follows a single consistent formula. It does not change from posture to posture. It does not change from the first routine to any subsequent practice. It is always the same.
Here is the formula:
When the weight is to the left, the knees are spiraling inward toward each other, compressing toward each other, and the body is rising up to the top of an arc. This is the moment of issuing power.
When moving from weight left to horse stance, meaning transitioning from left bow and arrow stance to center, the knees are spiraling outward away from each other, expanding away from each other, and the body is lowering down to the bottom of an arc. This is the moment of storing power, settling, sinking.
When the weight is to the right, the knees again spiral inward toward each other, compress toward each other, and the body rises up to the top of an arc. Again the moment of issuing power.
The pattern is rising and sinking, compressing and expanding, spiraling in and spiraling out. Always coordinated. Always the same regardless of which posture the body is in or which direction the form is moving.
Rising, Sinking, and the Arc
The arc deserves its own explanation because it is one of the most important physical qualities in Chen style practice and one of the least visible from the outside.
As the knees spiral inward and compress toward each other, the body does not simply hold its position. It rises. Not dramatically, not by straightening the legs fully, but through the springlike quality of the knees compressing that sends force upward through the body. This rising is the expression of power, the moment when the stored energy that has been built through the sinking and compression phase releases upward and outward through the waist, the arms, and the hands.
As the knees spiral outward and expand away from each other, the body sinks. Again, not dramatically, but with a quality of settling, of weight dropping more fully into the ground, of relaxation moving through the system from top to bottom. This sinking is what I mean when I say fangsong follows every issue of power. The moment power is expressed, the letting go begins. The body does not stay in the issued state. It releases back into sinking, into storage, into preparation for the next cycle.
This rising and sinking arc is what gives Chen style Tai Chi its characteristic quality of continuous undulation, even in what appear to be static postures. There are no truly static moments in the practice. There is always a cycle happening, even when the external observer cannot see it clearly.
For the foundational understanding of silk reeling and how it relates to this spiral principle, read The Complete Guide to Silk Reeling and Silk Reeling Exercises for Beginners.
The Waist in the Spiral
The knee spiral does not happen in isolation. It is always accompanied by a coordinated movement of the waist, and understanding their relationship is essential for correct practice.
When power is issued, the waist spirals in the direction of the issue. If the power is expressing to the right, the waist rotates to the right simultaneously with the knees compressing inward and the body rising. The waist is not leading the knees or following them. They move together as part of the same integrated whole-body action.
After the power is issued, as the knees spiral outward and the body sinks, the waist relaxes back to neutral. Not to the opposite direction, just to neutral, the balanced, centered position from which the next movement can arise freely in any direction.
This coordination of waist, knees, and body rise/sink is what makes Chen style power feel so different from the muscular force of external martial arts. The force does not come from one part of the body pushing. It comes from the whole body coordinating in a single integrated spiral that originates in the legs, passes through the waist, and expresses through the arms. The knees are not generating the power themselves. They are the visible expression of a whole-body coordination that produces the power.
For more on how this three-principle framework underlies all of Chen style practice, read The 3 Principles of Chen Tai Chi.
End of Posture: Always Sinking
One of the most important and most frequently misunderstood points in this principle is what happens at the end of any posture in the form.
At the end of a posture, meaning in the final settled position after the power has been issued and the body has completed its action, the knees are always spiraling outward and expanding away from each other, and the body is always sinking. Always. Without exception.
This is not because the weight has changed. The weight distribution of the posture, whether 70/30 or 50/50, remains exactly as it was during the issue. What has changed is that the issue/settle cycle has completed its arc. Power was issued in the rising, compressing, spiraling-in phase. The posture settles in the sinking, expanding, spiraling-out phase. The final posture is always the sinking phase, always fangsong, always a release back into the stored state that prepares for whatever comes next.
This means that if you look at a photograph of a correctly executed Chen style posture, you are looking at a body in the sinking phase. The knees are gently expanding outward. The weight is settled into the ground. The body is slightly lower than it was at the peak of the issue. This is correct. This is what the posture is supposed to look like.
Understanding this resolves a common confusion in beginners who try to hold the peak of the issuing moment as the posture. They end up in a state of sustained tension, the knees compressed inward and held there, the body elevated and braced. This is not a posture. It is a momentary peak of a cycle that is supposed to immediately release into sinking. Teaching students to release through that peak and settle into the sinking phase is one of the most important corrections in early Chen style training.
For more on the relationship between letting go and correct Tai Chi movement, see Chen Style Tai Chi Rule 1.
Knee Alignment: The Safety Principle
The knee spiral is a powerful training principle and it comes with a non-negotiable safety requirement: the knees must always maintain alignment with the feet and toes throughout the spiral. The direction the knee points must always match the direction the foot points. This alignment must never be compromised, regardless of how much the knees are spiraling or compressing.
When students get this wrong, typically by overdoing the spiral or by confusing spiraling with torquing, the result is one of three problems. The knee collapses inward past the toe line. The knee over-rotates in a way that loads the medial structures. Or the knee locks into extension, which removes the springlike quality entirely and prevents the knee from participating in the arc at all.
Each of these errors is a mechanical problem that causes real damage over time. The knee is not designed to absorb rotational forces applied when the foot is fixed on the ground. The spiral principle works precisely because the spiral stays above the foot rather than twisting across it. The knee spirals within the plane defined by the foot direction, not across it.
What I check for in my own practice, and what I check for in students, is that even at the peak of the inward spiral and compression, the knee cap is still tracking directly over the middle toe. If it has moved off that line, the spiral has become a torque and the principle is being applied incorrectly.
In the beginning students almost always overdo. They feel the instruction to spiral and compress and they exaggerate it. The correction is always the same: maintain alignment, reduce the amplitude, and focus on feeling the correct position rather than performing a visible movement. This feeling of correct position only comes through a teacher correcting the student enough times that they know from internal sensation what correct feels like. After that, the student can self-correct.
For more on the therapeutic effects of correct knee mechanics in Tai Chi practice, see Tai Chi for Knee Pain and Silk Reeling and Joint Health.
Why This Principle Changes Everything
Once a practitioner genuinely understands and can feel the opposing knee spiral principle, their relationship to the entire form changes. They stop thinking about individual postures as separate things to remember and start understanding every posture as a different configuration of the same underlying formula. Left weighted, spiral in, rise, issue. Transition through center, spiral out, sink, store. Right weighted, spiral in, rise, issue. The names of the postures become almost irrelevant. The formula is what they are all doing.
This is why Dr. Bob says it is not necessary to name different postures when teaching this principle. The postures are all the same this way. Understanding the formula gives you the key to every posture simultaneously rather than requiring you to learn each one separately.
This level of understanding takes time and qualified instruction to develop. You cannot feel the knee spiral correctly from reading alone. You need a teacher who can observe your knees, tell you when the alignment has broken down, and help you find the correct sensation through repetition and correction. But once you have the correct sensation, once you know from the inside what the proper spiral feels like, you can apply it to every posture in the practice and your entire form will begin to integrate in a way it could not before.
For the complete context of Chen style Tai Chi and what it develops, read The Complete Guide to Chen Style Tai Chi.
Frequently Asked Questions
Does the knee spiral direction change depending on which side is weighted?
No. This is one of the most important clarifications in this principle. The knee spiral direction is determined by the issue/settle cycle, not by which side is weighted. Both knees always spiral in the same direction simultaneously: both inward during the issue and rising phase, both outward during the settling and sinking phase. Whether the weight is left, right, or centered, and whether the weight is 70/30 or 50/50, the knee spiral direction follows the same rule. Weight distribution and the spiral direction are independent of each other.
How is the knee spiral different from simply bending and straightening the knees?
Bending and straightening is a linear movement in one plane. The knee spiral is a rotational component added to the flexion and extension, meaning the knees are not just moving up and down but also rotating inward toward each other or outward away from each other as they move. This rotational component is what engages the full spiral chain from the feet through the legs and into the hip and waist. Without the rotational component, you have leg movement but not silk reeling movement. The spiral is what connects the lower body movement to the whole-body coordination that makes Chen style power possible.
Why does the body rise when the knees compress inward and sink when they expand outward?
Think of the knees as the spring in the system. When the knees compress inward and toward each other, the leg structure is loading, storing elastic energy in the tendons and connective tissue of the lower body. This loaded spring releases upward through the body as the power is issued. When the knees expand outward, the spring is releasing, the energy discharges through the system and the body settles back toward the ground. The rise and sink are the visible expression of the spring loading and releasing. This is why Chen style power feels so different from muscular pushing: it has the quality of an elastic release rather than a sustained force.
How long does it take to develop correct feeling for the knee spiral?
With good instruction and daily practice, most students begin to feel the correct knee spiral direction within a few weeks of focused attention on the lower body silk reeling exercises. Applying it correctly throughout the entire form, where it must happen automatically across dozens of postures and transitions, takes considerably longer, typically months of daily practice with periodic correction from a qualified teacher. The principle is simple. The embodiment of it across the full complexity of the form is the work of sustained practice.
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