One of the hallmarks of taiji is a kind of strength called nei jin (internal refined strength). The writings of the Taiji Classics emphasize that in order to attain such strength, it is first necessary to relax completely. The idea of relaxing completely in order to become strong might sound like a contradiction that is impossible to resolve. After all, it would seem that strength must come from the contraction of muscles, which when totally relaxed would be unable to exert sufficient strength to do even the simplest movement.

In my view, the above seeming contradiction is resolved by understanding that, whereas strength derived from the contraction of muscles is well-known, it may not be the only way that strength can be achieved. What if there were another kind of strength involving the expansion of muscles and other tissues of the body by means of a hydraulic-like pressure, but that kind of strength would first need to be recognized and then trained? Of course such strength would seem impossible if there were no concept of it, or common name for it, and if its physiological mode were not studied scientifically. However, once you experience such strength, whatever its cause, you can have no doubt that it exists.

I learned about such strength from a dancer, Elaine Summers, with whom I studied in the 1970s because of problems I had with my back. At a certain point of practicing taiji, I realized that the strength she taught for movement and therapy was the same as nei jin. In order to develop such strength, it is first necessary to relinquish one's accustomed contractive strength which would mask experiencing any fledgling emergence of expansive strength.

First the advantages of expansive strength over contractive strength will be presented. Then some exercises will be provided for recognizing the difference between the two types of strength.

Advantages of Expansive Strength Over Contractive Strength

1. Control and Responsiveness. In using contractive strength, bones act as levers that produce large movement for a small movement of their controlling muscles. The price paid is that contractive strength is hard to regulate finely, and huge amounts of muscular tension are required to lift even the smallest weight, thereby rigidifying the body.

By comparison, expansive strength does not involve the bones. Because most of the movement in taiji originates from the shifting and turning of the torso, only small amounts of movement of limbs from expansive strength are required. The result is from small increments of expansion that occur throughout the entire body then add to produce a finely regulated way of moving.

2. Martial. Contractive strength is localized and, therefore, easily read by an opponent who can use that information to gain an advantage.

Expansive strength is hidden (the Taiji Classics use the word concealed) and is not easily read. Moreover, tiny amounts of such movement can move through the body like a wave and result in a large, powerful movement of a limb (fajin).

3. Endurance. Muscular contraction consumes a large amount of chemical fuel and produces irritating by-products. The contraction cuts off blood circulation, thereby halting transport of new fuel into muscles and waste products away. Thus muscles soon fatigue, and contraction can be sustained for only a short time, with muscles soon becoming painful.

Expansive strength requires little chemical energy and, therefore, can be maintained for long periods without fatigue.

4. Health. Whereas contractive strength cuts off blood and qi, expansive strength is relaxed and even stimulating to the flow of blood and qi. Thus use of expansive strength has a healing and exhilarating effect.

5. Root. Contraction involves muscles pulling bones. Thus, when a practitioner exerts strength against an opponent, the opposite ends of the muscles involved are pulling the practitioner out of his or her root.

Expansion involves pushing, so the opposite ends of the muscles and other bodily tissues involved are pushing the practitioner into his or her root. Thus expansive strength increases root.

6. Protection. In a state of contraction, the body is less susceptible to injury from a blow. But for reasons mentioned in (3) above, it is impossible to sustain a continuous state of contraction.

Expansion is not only more protective than contraction, but it can be sustained continuously.

Exercises for Recognizing the Difference Between the Two Types of Strength

Here are some exercises from my book, Tai Chi Concepts and Experiments, that can help in recognizing expansive strength.

Experiment 1. Opening Your Hand. Sit or stand, and relax as much as possible. Hold your arm in front of you such that your hand is relaxed and a comfortable distance from your body. Imagine that you have an expanding balloon in the palm of your hand. Remember that it is important not to do any actual movement at first. Then, very slowly open your hand a tiny amount, imagining that doing so is a result of the expanding balloon. Pay special attention to the feeling of the palm of the hand and the inside of the forearm as compared to the back of the hand and the outside of the forearm. See how open you can make your hand without losing the feeling just referred to.

Experiment 2. Expanding and Releasing the Space between Your Fingers. Repeat the elements of the previous experiment, this time slightly opening the space between your fingers. Then allow the fingers to resume their natural, released spacing.

Experiment 3. Rotating Your Wrists. Stand with feet parallel. Extend one arm (say, your left arm) forward, in front of the body. Let the wrist find its neutral orientation (neither rotated to the right nor to the left). Next, rotate your palm downward in two different ways:

(a) The contractive way is to pull your left palm heel downward by contracting the muscles on the inside of your forearm and to pull your little finger upward by contracting the muscles on the outside of your forearm. This is the conventional way of moving by using contractive strength.

(b) The expansive way is to push your left palm heel downward by extending the muscles on the outside of your forearm and to push your left little finger upward by extending the muscles on the inside of your forearm. Notice that in this way of moving, the hand does not rotate fully, but in the first case it easily can. Also compare the amount of qi in your hand for the two ways.

Experiment 4. Extending Your Hamstrings. Stand with feet parallel. Lean forward and let your upper body hang from your hip joints, knees slightly bent. Relax your head, arms, and back as much as possible. Remaining so, next try lifting the pelvis in two different ways:

(a) The contractive way is to push the knees back, causing your legs to straighten. In this case, the muscles on the back of the legs are forced to lengthen by the contraction of muscles on the front of the legs. This is the conventional way of stretching.

(b) The expansive way is to extend the legs by lifting the hip joints by extending the muscles on the back of the legs. These muscles lengthen by their own action rather than being forced to do so by contraction of the muscles on the front of the legs. Notice that in this way of moving, the legs do not totally straighten, but in the first case they easily can.


Once you are able to totally relax and can recognize the difference between contractive and expansive strength in all movement, you are on your way to cultivating nei jin. Eventually your expansive strength will increase, and so will the resulting health and martial benefits.

The above is an original article by Robert Chuckrow, Ph.D., author of Tai Chi Concepts and Experiments: Hidden Strength, Natural Movement, and Timing, pub date April 2021, YMAA Publication Center, ISBN 978-1-59439-741-7