Body and Breath

Each month a new series of 10 questions will be posted on the Test Yourself page. The following month the questions will then be posted here along with the answers and explanations.

Answers to the January 2002 questions are posted below. ( View Archive )

Note: For each of the following questions (one for each chapter in Anatomy of Hatha Yoga), please answer in 100 or fewer words using complete sentences.

71. Briefly explain the meaning of "concentric shortening" of a muscle as contrasted to "eccentric lengthening," and give one example of each.

Answer: Concentric shortening of a muscle refers to the most easily conceived situation in which a muscle shortens as a result of being stimulated by the nervous system. Eccentric lengthening of a muscle, by contrast, refers to maintaining tension in a muscle as it is lengthening, specifically while it is resisting the force of gravity. When you step up onto a platform, the extensor muscles of your lower extremities shorten concentrically, and when you step back down, the same muscles lengthen eccentrically.

72. Explain how it happens that a spinal cord transection at C7 results in paralysis of all four extremities and yet spares the function of the diaphragm, which is located at the base of the chest.

Answer: The nerves that supply the extremities enter the spinal cord BELOW the spinal cord transection (via the brachial plexus for the upper extremities and via the lumbosacral plexus for the lower extremities), so the brain is completely disconnected from the motor neurons that control the extremities. The nerves that supply the diaphragm, however (the phrenic nerves), exit the spinal cord from ABOVE a spinal cord transection at C7, namely from C3-5, and from there course away from the spinal cord and vertebral column and then downward to the diaphragm. Thus the brain continues to control the motor neurons that in turn innervate the diaphragm.

73. Why is a simple double leglift lying flat on the floor a more advanced exercise than the fire exercise?

Answer: Lying fully supine, a double leglift places tremendous tension on the lumbar region even as the hip flexors flex the thighs (lifting the feet off the floor and up in the air while keeping the knees straight). It is thus a challenging and advanced exercise to keep the back flat against the floor during a supine double leglift. By contrast, doing a double leglift in the fire exercise (which features keeping the back rounded to the rear and keeping the head and shoulders forward) stabilizes and thus protects the lumbar region as the hip flexors lift the thighs.

74. Picturing a frontal plane (side-to-side, up-and-down plane) through the body from head to foot in the mountain pose, what structures does a plumb line of gravity pass through with reference to the head, neck, torso, hip joints, knee joints, and ankles? And second, why is this important in hatha yoga?

Answer: A plumb line of gravity passes through the top of the head, through the cervical and lumbar vertebral bodies (it passes in front of the thoracic spine and sacrum), behind the axial center of the hip joints, in front of the axial center of the knee joints, and in front of the ankle joints. The passage of a plumb line of gravity through the body is important to us in hatha yoga because it keeps us aware of precise adjustments that are constantly made in the body with respect to gravity.

75. What are the outside limits for back and for hip extension, and what are the limits for those who have excellent flexibility, but that is still within a normal range?

Answer: The outermost limit for back extension, which is seen in a few individuals who can bend so completely in the lumbar region that they can lay their upper backs down against their hips, is 180 degrees. The outermost limits for hip hyperextension appears to be about 45 degrees. A reasonable norm of excellent flexibility for extension that allows one to do even advanced yoga backbending postures is about 70 degrees for lumbar backbending and 20 degrees for hip hyperextension, which totals 90 degrees.

76. Why is sacroiliac nutation and counternutation important in forward bending?

Answer: Sacroiliac nutation and counternutation is an important factor for all backward and forward bending postures. For example, if you have a healthy mobility in the sacroiliac joints, you will come to the limits of nutation as a preparation for "bending forward from the hips." If you are struggling to do forward bends, you will approach them of necessity by "bending forward at the waist," and this will likely be initiated from an attitude of counternutation. This is just the beginning. If you have some sacroiliac mobility, you will find yourself being very observant of how nutation and counternutation contribute to all forward and backbending postures, as well as how the movements are important to other activities.

77. Why are simple cross-legged sitting twists so important for beginning students in hatha yoga?

Answer: These are important postures because they are often the only sitting twists in which beginning students are comfortable. Traditional half spinal twists are wonderful postures, and are worthwhile even for beginners to study, but they should always be compared with and contrasted to simple cross-legged twists. Students will then be better able to sense and understand exactly how and why half spinal twists are more challenging than simple cross-legged sitting twists, and just as important, how and why half spinal twists are uniquely valuable for improving hip flexibility.

78. How does it happen that the same amount of blood (approximately 5-6 quarts) is pumped to the lungs per minute as is pumped to the body as a whole?

Answer: The same amount of blood is pumped to the lungs per minute as to the body because the blood moves through two sequential circuits (pulmonary and systemic), from the right ventricle (pulmonary circulation arteries) to the lungs and back (pulmonary circulation veins) to the left atrium, from the left atrium to the left ventricle, from the left ventricle (systemic circulation arteries) to the body, from the body (systemic circulation veins) to the right atrium, and from the right atrium to the right ventricle, at which point the blood is again pumped to the lungs.

79. Why are the arch and bridge postures useful as a) substitutes, b) preparations, and c) complements for the full shoulderstand series?

Answer: The arch and bridge poses are especially valuable for novices as substitutes for the shoulderstand series because they accustom beginning students to flexion of the neck without the necessity of lifting the feet up in the air or pulling them up and then overhead. They are valuable as preparations for the same reasons. These poses also complement the shoulderstand series because they are mild backbending postures that contrast with the forward bending tendencies of the plow, shoulderstand, and other inverted or semi-inverted postures (excepting the headstand, which likewise can exhibit backbending tendencies).

80. What is the enteric nervous system, why was it neglected by researchers and ignored by teachers after its initial description a century ago, and why is it likely to become more important as it is more widely understood and appreciated?

Answer: The enteric nervous system is the intrinsic nervous system of the digestive tube. It can by definition operate independently and without supervision from the brain and spinal cord. It was neglected until the 1980s because no one realized its complexity or knew what to say about it. It will probably become more important in the minds of biological scientists and physicians in the future because exploring it will probably help clarify and unravel many medical enigmas of the digestive system. It may also prove important in the "gut feelings" of emotional expression, and if that happens, the system will certainly catch the attention of experimental psychologists.