Muscular Strength: Advantages of Expansion Over Contraction in T’ai Chi

©Copyright 2017 by Robert Chuckrow

The following analysis is an amplification of parts of my book, Tai Chi Dynamics1. Also, it may be worthwhile to read another article on this website, Is Muscular Extension Possible?, in which scientific and experiential evidence is presented to support the hypothesis that muscles can extend as well as contract.

Briskness of Regulation of Strength (Quick Adaptability)

Use of contractive strength. When contractive muscular strength is employed, nerve impulses from the brain and spinal cord cause muscle units to contract. The contracting muscles pull bones by means of their associated tendons, thereby producing external force and movement. When external conditions require a change in the contraction produced, a number of stages must occur in succession: 1) Afferent nerve impulses arising from sensory stimuli (sense data) are transmitted to the central nervous system and brain for analysis. 2) The analytical part of the brain then perceives the need to regulate external force and movement in accordance to what is perceived. 3) Based on the perceived need, the analytical mind then generates a course of action. 4) Efferent (motor) neural impulses are then sent to muscles, causing force and movement for the required change. The time taken for this succession of neurological events can be long compared to the time in which external conditions can change, especially in a self-protection situation.

Use of expansive strength. When expansive muscular strength is used, all contractive strength is released, allowing the body to liquefy. When strength is required while in this liquefied state, nerve impulses that normally are utilized to cause muscles to contract, instead, cause the water in the muscle cells to expand and, thereby, become pressurized. This pressure pervades the whole body. A principle in physics, called Pascal’s principle, states that, “Any change in the pressure at any point in a confined liquid is accompanied by the same change in pressure at every other point.” During the exertion of external force, if any increase or decrease is required by external conditions, there is no need for any neurological activity or analytical processing; because of Pascal’s principle, as soon as there is a sudden increase or decrease in external force, the hydraulic pressure within the body automatically adjusts, virtually instantaneously.


One important distinction between contractive and expansive strength applies to the exertion of force on you by an opponent (or the exertion of force by you on him). A basic principle in physics that governs situations involving the application of force of one body on an other is Newton’s third law, which states: “If object A exerts a force on object B, then B exerts an equal and opposite force on A.” This law applies to all bodies—sentient or not, stationary or moving. A corollary of Newton’s third law is that it is impossible to exert a force on another person or object without that person or object exerting the same force back on you (See Fig. 1).

An example of Newton’s third law

Fig. 1. In part (a), a person is pushing a door with a force of magnitude F to the right. Part (b) shows the force exerted by the person on the door. Part (c) shows the reaction force of an equal magnitude F to the left, exerted by the door on the person. It is a consequence of Newton’s third law that, when a person exerts a force on a door, the door exerts an equal-and-opposite force on the person. This result holds whether the door moves or not!2

Thus, when someone exerts force on your body with his hand, before you even do anything, your body automatically exerts a force back on his hand that is exactly equal in magnitude and opposite in direction to the force his hand exerts on your body. Similarly, when you place your hand on someone’s body, now another two forces come into play. One is the force that you are exerting on his body with your hand. The other is the equal and opposite force exerted on your hand by his body.

In T’ai Chi, Newton’s third law comes into play in causing an opponent to lose his balance (called “breaking the opponent’s root”) as follows: If an opponent A exerts a force F on me, according to Newton’s third law, I automatically exert the same force F on A in the opposite direction (the reaction to his force). In order to remain in balance, A must arrange things so that the total frictional force of the floor on his feet exerts a force that is opposite to the force I am exerting on him (the force I am exerting on him is the reaction to his force on me). If either of these two forces on A is removed or changed, A’s balance will be lost until he readjusts the forces on himself (see Fig. 2 for the forces involved).

All forces on man pushing a wall

Fig. 2. All of the forces on person A pushing person B are shown and labeled: FA is the force on A, which is a force that is equal and opposite to the force that A exerts on B (the reaction to A’s force on B). W is the weight of A (the gravitational force exerted by the earth on A’s center of mass). FN1 is the upward force the floor exerts on A’s rear foot, and FN2 is the upward force that the floor exerts on A’s forward foot. Note that the sum of FN1 and FN2 is a force equal and opposite to W (A is balanced in the vertical direction). Ff1 is the frictional force that the floor exerts on A’s rear foot, and Ff2 is the frictional force that the floor exerts on A’s forward foot. Note that the sum of Ff1 and Ff2 is a force equal and opposite to FA (A is balanced in the horizontal direction).3

Assume that A exerts a force on me. Because I have control over the intensity of my force on A, I can regulate and then suddenly release that force, causing FA to momentarily go to zero. In order for A to restore his balance in the horizontal direction, A must promptly reduce the frictional forces of the floor on his feet. That requires a prompt reduction of the force of his feet pushing backward on the floor. If A is using contractive strength, then the time A takes to recover his balance is long enough for me to take advantage of it, and I can easily send A flying. However, if A is using expansive strength to exert force on me, then the hydraulic pressure everywhere within every part of A’s body automatically releases instantaneously, thereby preventing any imbalance that I might take advantage of.

Endurance and Health Benefits

During the time that muscles are in a state of contraction, the flow of blood and ch’i are suspended. The consequent interruption of oxygen, nutrients, and cellular movement and the interruption of metabolic waste removal all serve to limit the amount of time that muscles can remain in a state of contraction without tiring. Alternatively, exertion of expansive strength does not result in such undesirable effects and can, therefore, be sustained far longer. If anything, a state of expansion increases the circulation of blood and ch’i (qi). This increase can be felt and can even be seen as a substantial increase in coloration in one’s extremities.

Another health issue is that habituation to muscular contraction can lead to “frozen tension,” which is a state in which muscle fibers remain contracted independent of any need for being so. “Frozen tension” is analogous to driving a car with one foot on the gas and the other on the brakes, which is not good for a car because it wastes gas and produces wear on and even damage to the braking system. Corresponding ill effects occur in a human body including the limitation of adaptational movement, thereby increasing the probability of injury.

With age (and also the lack of nutrients, proper bodily usage, exercise, exposure to an optimal amount of sunlight, hydration, and sufficient sleep), it is common for the thoracic spines of many people to increasingly curve forward. In that state, it is impossible for muscular contraction of the back muscles to support the spine in an optimal posture for more than a short time—if at all. Here is where muscular expansion of the front of the trunk of the body can make a big difference in supporting the trunk. Practicing upward and lateral expansion of the front of the chest can slow down the progression of the forward curvature, or arrest its progression. In some cases the excessive curvature can be somewhat reversed.

Fine-Motor Control

We are most familiar with the lever shown in Fig. 3. Here force applied at P is multiplied by the ratio of the distance of P to the fulcrum divided by the distance of the fulcrum to the weight W being lifted. That ratio is about 2:1. Thus, the applied force required is only about half the weight of the stone. At the same time, the movement at P is correspondingly about twice that of the weight.

Lever lifting a Rock

Fig. 2. A familiar lever that multiplies applied force and reduces motion.4

In Fig. 3, which shows an arm lifting a weight, the biceps tendon applies a force at P, and the fulcrum is at the elbow. In this case, the situation is reversed from that of Fig. 2; namely, the motion of the weight is much greater than the applied force, and the applied force is much greater than the weight being lifted. This compromise between strength and mobility evidently has evolved based on its survival value for our ancestors.

Lever lifting a Rock

Fig. 3. A less-familiar lever that multiplies motion and reduces force.5

The result of the above physiological relationship between arm strength and motion results in a lack of fine motor control when strength from muscular contraction is utilized. However, when strength from muscular expansion is applied, no such lack occurs.

An Analysis of Cheng Man-ch’ing’s Distinction Between two Different Types of Strength

The excerpt below was written by my first T’ai-Chi teacher, Cheng Man-ch’ing.6 Note that the quoted text is an English translation of Prof. Cheng’s original book, which was written in Chinese. In order for such a difficult subject to be properly translated, the translator would not only need to be fluent in Chinese and English but also adept at the subject discussed.

When the body is emptied of force, a “tenacious strength” will develop from the foot. Tenacious strength may be distinguished from force in that the former has root in the foot while the latter has not. When in action, tenacity may be likened to a strong vine which is pliable, and force to a stick which is rigid. Hence we say: "tenacity is alive, force is inert." Tenacity is the resilience or tonicity of living muscles however relaxed they may be. The muscles being relaxed, tenacity cannot involve the bones. Force, on the other hand, is derived from binding the bones together into a wooden (rigid) system. Tradition has handed down, as a secret formula, that “tenacity is derived from muscle; force, from bones.”

I have rewritten the above translation below, replacing force by contractive strength and tenacity by expansive strength:

When the body is emptied of contractive strength, a “tenacious strength” (expansive strength) will develop from the foot. Expansive strength may be distinguished from contractive strength in that the former has root in the foot while the latter has not. When in action, expansive strength may be likened to a strong vine which is pliable, and contractive strength to a stick which is rigid. Hence we say: “Expansive strength is alive, contractive strength is inert.” Expansive strength is the resilience or tonicity of living muscles however relaxed they may be. The muscles being relaxed, expansive strength cannot involve the bones. Contractive strength, on the other hand, is derived from binding the bones together into a wooden (rigid) system. Tradition has handed down, as a secret formula, that “expansive strength is derived from muscle; contractive strength, from bones.”

Here is my attempt to further elucidate what Prof. Cheng wrote:

As you release contractive tension, there is a feeling that the whole body becomes liquefied. Then, as you shift and sink into a foot during a transition, it feels like the liquid in your body is thereby compressed and expands everywhere, especially into your arms. However, it helps to additionally send the right neural electricity to enhance the expansive effect. That's where reverse breathing can be an important tool. Reverse breathing involves expanding the diaphragm, which sympathetically produces an expansive effect throughout the body. Once that effect is recognized and practiced, it can be done independently of any particular way of breathing.

Whereas any movement can be utilized for working on expansion, the very first move (“Preparation”) is an especially good one. As I release and sink into my right foot, I use my intention to correspondingly pressurize the liquid in my arms, causing them to expand slightly outward from my body. As I turn to the right, I use that expansion to rotate my arms so the palms face the rear. The Preparation movement symbolizes the separation of yin and yang. Sinking into the right foot causes it to be yin (yielding, supportive, earthy). The result is the production of yang in the arms and left leg (active, expansive, upward, outward).

Both expansion and contraction involve muscular action, so at the beginning, it is hard to distinguish between those two types of strength. So if you are in doubt as to whether or not you are actually expanding instead of contracting, it is possible to check by then contracting the muscles in your arms and feeling the difference, which should be quite noticeable.

Everyone can produce expansive strength—it’s mainly a matter of recognizing how to do it. Try yawning intensely, and feel the effect throughout your body. Try expanding your lower abdomen or your diaphragm. Once you recognize the feeling, then recreate and practice doing it increasingly fully and intensely.

Prof. Cheng also talked about imagining the air to have the resistance of water,7, 8 which in my opinion is another tool for recognizing expansive strength. He said that eventually, the air will feel like it has the resistance of iron!9 This feeling of extreme resistance is something that I routinely experience when fully activating expansive strength. (See my article Swimming on Land.)

Expanding and Condensing

One of my more-recent T’ai-Chi teachers, Sam Chin Fan-siong, frequently emphasized what he called expanding and condensing. By those words, he meant that the yang part of each movement involves an expansion of strength originating from the centers of the feet, and the yin part of each movement involves a partial decrease in expansive strength. Whereas English was not Chin’s native language, he used English words with great thought, care, and precision. Both expanding and condensing are beautifully apt words—especially condensing. Chin writes about use of correct force in his book on I Liq Chuan.10

In physics and chemistry, the term condensing applies to a confined gas in which the motion of the molecules of the gas decreases. This slowdown results in the molecules hitting the walls of the container (a) with less force and (b) less frequently. Each of these factors causes a decrease in the pressure on the walls of the container enclosing the gas. That is, condensing implies a decrease in outward pressure—not anything pulling inward as in the case of contraction. The use of any contractive strength, which implies “pulling” inward, is therefore inconsistent with Chin’s use of expanding and condensing.

Prof. Cheng Man-ch’ing described “attracting” an opponent’s force and then discharging it, which he called “receiving energy.” He said that such an ability was the highest level of T’ai Chi and is different from using force against force.11

Another teacher of mine, Harvey Sober, spoke about a similar concept of absorbing the opponent's energy and then “spitting” it out.

1Robert Chuckrow, Tai Chi Dynamics, YMAA Publication Center, Inc., P.O. Box 480, Wolfeboro, NH, 2008, pp. 47–54.

2This figure was reproduced from Robert Chuckrow, Tai Chi Dynamics, YMAA Publication Center, Inc., P.O. Box 480, Wolfeboro NH 03894, 2008, p. 49.

3Not all equal-and-opposite forces are action/reaction—equal-and-opposite forces that are on the same object are never action/reaction.

4This figure was reproduced from Edward R. Shaw, Physics by Experiment, Maynard, Merrill, & Co., New York, 1897, p. 16.

5This figure was reproduced from Edward R. Shaw, Physics by Experiment, Maynard, Merrill, & Co., New York, 1897, p. 28.

6Cheng Man-ch’ing, T’ai Chi Chuan: A simplified Method of Calisthenics for Health & Self-Defense, North Atlantic Books, Richmond, VA, 1981, pp. 16 – 17.

7Cheng Man-ch’ing, Tai Chi Chuan: A simplified Method of Calisthenics for Health and Self Defense, North Atlantic Books, Berkeley, CA, 1985, p. 10.

8Cheng Man-ch’ing and Robert W. Smith, T’ai Chi: The “Supreme ultimate” Exercise for Health, Sport, and Self Defense, Charles E. Tuttle Co., Rutland, VT, 1967, p. 12.

9Cheng Man-ch’ing, Cheng Tzu’s Thirteen Treatises on T’ai Chi Ch’uan, Translated by Benjamin Pang Jen Lo and Martin Inn, North Atlantic Books, Berkeley, CA, 1981, p. 39.

10Sam F.S. Chin, I Liq Chuan: Martial Art of Awareness, Chin Family I Liq Chuan Association, P.O. Box 374, Mount Kisco, NY, 2006, pp. 68–69.

11Cheng Man-ch’ing, Tai Chi Chuan: A simplified Method of Calisthenics for Health and Self Defense, North Atlantic Books, Berkeley, CA, 1985, pp. 124–5.

Related Article: Cultivating the Correct Internal State in T’ai-Chi Movement

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