Z94.2 - Anthropometry & Biomechanics: Biomechanics Section
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VASOCONSTRICTION. Decrease in the cross-sectional area of blood vessels. This may result from contraction of a muscle layer within the walls of the vessels or may be the result of mechanical pressure. Reduction in blood flow results. Vasoconstriction can be controlled by the nervous system and is influenced by certain drugs. Improper design of the man equipment interface (q.v.) may cause vasoconstriction, i.e., poor seat design, improper tool handles.
VELOCITY SIGNATURE. An analogue recording which shows the velocity history of a body part in motion. Signature size and shape are indices of strength and motor skills of an individual. Repeatability of velocity signatures in indicative of status of health, fatigue and/or training. An important component of the biomechanical profile (q.v.).
VERTEBRA. One of the irregularly shaped bones of the spine (q.v.). The anterior portion, known as the vertebral body, is the load bearing component of the stucture. The posterior portion provides muscle attachment points, longitudinal passage of the spinal cord, exits for the spinal nerves (q.v.), and stabilizing surfaces for adjoining vertebrae which also regulate motion and are load bearing under certain circumstances. (See SPINOUS PROCESS OF THE VERTEBRA, VERTEBRAL COLUMN).
VERTEBRAL COLUMN. Bony structure commonly known as the spine. Provides the primary supporting structure of the trunk of the body, and houses and protects the nerves of the spinal cord. Extends from the head to the coccyx. Consists of 24 bones (vertebrae) separated by shock-absorbing inter-vertebral discs (q.v.). Trauma to the vertebral column (shock, twisting, compression, fracture, or stretching) can cause severe pain and/or disability. Curvature of the vertebral column is an important factor in the design of seats. (See vertebra, spine, spinous process.) Note: Because of the irregularities (especially at the lower end of the spinal column), texts may differ in their count of the number of vertebrae. E.g., Dorland's Illustrated Medical Dictionary defines, vertebrae as " any of the thirty-three bones of the spinal column, comprising seven cervical, twelve thoracic, five lumbar, five sacral, and four occygeal vertebrae." Blakiston also lists 33. In lay terms, the five regions of the spinal column are: cervical (neck), thoracic (chest), lumbar (lower back), sacral and coccygeal (both in the pelvis). The first three regions have separate and movable vertebrae throughout life, but, in the adult, the sacral and coccygeal vertebrae become fused to form the sacrum and coccyx. This fusion and, hence, resulting irregularity in the lower regions give rise to what may seem to be contradictions in texts to lay readers. Again, there may also seem to be confusion at the other (upper) end, depending on whether the uppermost bone is considered part of the skull or spinal column. Thus, it may be noted that the 35th Edition (British) of Gray's Anatomy lists 31 vertebrae (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal). Thus, orthopedists are quite definite when they note, for example "slipping of L5 over S1'' (referring to the "fifth lumbar" and "first sacral") probably one of the most common of lower back ailments. Fifth lumbar vertebra (q.v.).
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