Some yoga postures stress the joints of the body to stimulate their strength and flexibility. There are two fundamentally different types of stress: tension and compression. Yogis need to know the difference between the two.
Tension is the familiar sensation of tissues being stretched. Compression is the sensation of tissues being pressed or pushed together. Both of these stresses are beneficial if done in moderation.
When a yogi is stretching a joint, he is stretching a ligament, a tendon, or both. When a yogi is compressing a joint, he is compressing bones. We can make these distinctions clearer with some simple hand exercises. The lessons we learn with our hands apply to all the other joints of our body.
Practical Hand Study
The forearm houses the muscles most responsible for clenching the fist or extending the fingers. If you palpate (touch) and squeeze the muscles of the forearm starting near the elbow and work toward the wrist, you should notice that the muscles are soft and malleable nearer the elbow but become smaller, harder and more string-like nearer the wrist. These string-like structures are actually tendons. They are extensions of the forearm muscles, and they connect the muscles with the finger joints. The tendons on the back of the hand extend and spread the fingers to open the palm. The tendons on the palm side of the hand close the fingers into a clenched fist. Muscles shorten and become hard when contracted. They lengthen and become soft when relaxed. The tendons feel tough and fibrous whether the muscles are tensed or relaxed.
To experience this phenomenon, palpate the muscles of your forearm near the elbow while alternately extending your fingers and clenching your fist. You should be able to feel the muscles tense and relax. But if you palpate your wrist while extending and clenching your hand, it should feel very different. The tendons near your wrist don't tense and relax the way muscles do; they are simply pulled and released by the muscles of the forearm.
When muscles contract, the tendons pull on the bones and the joints are compressed. This limits their range of motion but makes the joints more stable. A simple example should make this clear.
First, use your left hand to wiggle and bend the fingers of your right hand while it is relaxed. The joints of your right hand fingers are easy to bend and straighten. Take hold of the middle finger of your right hand and gently pull on it. You should be able to feel the joint of the first knuckle gently stretching as you pull and release your middle finger. This is only possible because your muscles are relaxed.
Now extend the fingers of your right hand as hard as you can and stretch the palm open. If you maintain this tension it is very difficult to pull and stretch the knuckle of the middle finger as before. This is because the tendons are pulling on the bones and compressing them together. This makes the joint more stable but less mobile.
Muscular Tension in Action
Muscular tension compresses the joints and thereby limits their range of motion. Sometimes this is desirable, and sometimes it isn't. If you wish to prevent a joint from reaching its full range of motion, muscular tension is favorable. But if you are attempting to stretch the joint to its full range of motion, muscular tension is not a good idea.
Try this exercise and remember that we apply these same principles to the other joints of the body as well: Extend the fingers of your right hand. Try to extend them so that your first knuckles are extended or “bent” back toward the back of your wrist. For many people this movement is very subtle.
Now, keep the fingers extended and also use your left hand to push them back further. Using the leverage of the left hand, you can bend the knuckles farther back.
But to bend the fingers back as far as possible, we need to relax the muscles of the right hand completely. With the right hand relaxed, use your left hand to push the fingers back as far as you can. This is usually a much greater range of motion than when the muscles are tensed.
Muscular passivity not only allows the greatest range of motion, it is also the least compressive to the joint tissues. This is why a chiropractor or osteopath often prefers to make sure the muscles surrounding a joint are relaxed before attempting a therapeutic manipulation.
Balancing Yin and Yang
We can use this simple experience to compare the benefits of yin yoga, yang yoga, and such regular yang exercises as weight training. In our simple experiment, we would classify the attempt to bend the fingers back using only muscle as regular yang exercise. Using the leverage of the left hand while the muscles are tense is a yang form of yoga. Using the leverage of the left hand while the muscles are relaxed is a yin form of yoga.
Yang exercise is always accompanied by compression of the joints. Compression is good for joints and stimulates the bones to healthy growth. This is one reason why vigorous yang exercise is prescribed to prevent osteoporosis. But yang exercise doesn't allow the full range of motion. Yang exercise develops strong muscles and bones but can leave the joints contracted and stiff. This is common among athletes.
Bending the fingers using leverage and muscle tension is a yang form of yoga. It develops strength and increases the range of motion. This is why yang yoga leaves a practitioner feeling more stretched and relaxed than yang exercises such as weight training.
Bending the fingers using leverage while the muscles are relaxed is a yin form of yoga. Yin yoga safely—even pleasantly—develops the full range of motion of a joint. This type of practice leaves the practitioner feeling relaxed, light, and free.
Yin yoga by itself won't develop the strength and stability a joint needs. Yang yoga by itself will not exercise the full range of motion. This is why different forms of yoga can and should be practiced as supplements to each other.
In conclusion, while joint stress is useful, it is not always desirable to stress a joint to its full range of motion. It is possibly dangerous to stretch a joint to its full range of motion when standing or moving. While yogis can explore the full range of motion of a joint, it should be done very slowly, patiently and with only moderate force.
Paul Grilley has been studying and teaching yoga since 1979. His special interest is in anatomy. He teaches regular workshops on physical and energetic anatomy. Paul lives in Ashland, Oregon with his wife Suzee.