V
vaccination administration of antigenic material (vaccine) to induce active artificial immunity to specific infections. Important to prevent disease in sporting groups, especially with widespread foreign travel. See also immunity.
vagus nerves the tenth pair of cranial nerves, originating from the brain stem and descending through the neck, thorax and abdomen, giving off branches with both afferent and efferent components to many organs and tissues. The efferent fibres are mainly part of the parasympathetic nervous system, including those that slow the heart and those that innervate smooth muscle and glands in the respiratory and gastrointestinal tracts. The main afferent fibres are visceral afferents from thoracic and abdominal organs.
valgum, valgus angled inwards – deviation away from the midline of the body, of a part distal to a joint, e.g. genu valgum where the tibia is deviated laterally in relation to the femur, resulting in a ‘knock-kneed’ appearance in adults, often due to osteoarthritis of the knee joint. Opposite of varum, varus. See also hallux.
value–expectancy theory see expectancy–value theory.
varum, varus angled outwards – deviation towards the midline of the body, of a part distal to a joint, e.g. genu varum where the tibia is deviated medially in relation to the femur, resulting in a ‘bow-legged’ appearance in adults. talipes varus inward tilt of the distal part of the foot at the talonavicular joint resulting in a club foot. Opposite of valgum, valgus.
vasoconstriction narrowing of the lumen of a blood vessel, due to contraction of the smooth muscle in its wall, mediated by neural (autonomic) control, local or blood-borne chemical factors, or fall in temperature. Part of the rationale for the use of ice in acute injury to minimize blood flow (and therefore swelling) in the damaged tissue.
vasodilatation widening of the lumen of a blood vessel, due to relaxation of the smooth muscle in its wall, mediated by neural (autonomic) control, local or blood-borne chemical factors, or rise in temperature. Syn vasodilation.
vasopressin syn antidiuretic hormone (ADH) see hormones, hypothalamus, osmoreceptors, posterior pituitary, thirst.
vector a variable, quantity or measurement that has both size and directional components. Cannot be added arithmetically due to directional component.
vegan diet consists totally of vegetables, vegetable oils and seeds, excluding all foods of animal origin – meat, fish and dairy foods, and also honey. Vegans need to make sure that they are getting enough protein and micronutrients such as iron and vitamin B12.
vegetarian diet excludes any meat, fish, seafood or animal-body by-products such as gelatine, but usually allows milk, cheese and eggs; lactovegetarian diet excludes all animal-body foods and eggs but does allow milk and milk products; lacto-ovo-vegetarian diet, the most liberal, excludes all animal-body foods, but includes milk, milk products and eggs.
velocity rate of change of position with respect to time. A vector quantity so has both magnitude (speed) and direction; linear velocity the linear displacement per unit time; angular velocity the angular displacement per unit time, i.e. speed of rotation in a particular direction (e.g. clockwise or anticlockwise); instantaneous velocity velocity of a body or object measured over a very short (infinitesimal) period of time: effectively a continuous measurement of velocity; tangential velocity the velocity of an object or body acting at a tangent to its direction of motion (often when it is moving in a circle or around a curve). See also displacement.
venous return the flow of blood from the whole body (except the lungs) via the great veins to the right side of the heart. Apart from minor beat-by-beat variations, this is equal at any one time to the cardiac output (from each of the ventricles), as the whole circulation, with the systemic and pulmonary components in series, is a closed loop. When heart rate increases and muscle supply vessels dilate in exercise, stroke volume is maintained (so that cardiac output is increased) by an increase in venous return, assisted by constriction of peripheral veins, reduction in the blood flow to the abdominal organs, and by the ‘pumping’ effects of increased depth of breathing (promoting flow into the thorax), and of the contracting muscles, which ‘milk’ blood along their local veins towards the heart.
ventilation in physiology and medicine, refers to pulmonary ventilation, the movement of air in and out of the lungs, whether during normal breathing, or by artificial means. total ventilation or minute volume 
E (or 
I) is the volume breathed out (or in) in litres per minute: the tidal volume multiplied by the number of breaths per minute. May be measured, e.g. by collecting the expired gas over a known time (Douglas bag method), or by integrating inspired or expired airflow with respect to time (by pneumotachograph). The effective component, alveolar ventilation 
A, refers to that which reaches the regions of the lungs where gas exchange occurs, and is equal to the total ventilation minus dead space ventilation 
D. Normally, at rest, 
A : 
D = 2:1 or typically, 
E − 
D = 
A, 6 − 2 = 4 L.min−1. When ventilation increases in exercise, the dead space is unchanged, so 
D rises only in proportion to the rise in frequency of breaths, but 
E rises relatively more as tidal volume also increases. See also artificial ventilation, dead space, lung volumes and capacities.
ventilatory equivalent describes the ratio of ventilation (minute volume) to oxygen intake, or to carbon dioxide output. For oxygen, the volume of gas breathed out (and in) in litres per minute (ventilation, 
E) divided by the oxygen consumption in litres per minute (
O2) over the same period: an index of the efficiency of oxygen uptake in the lungs. When there is significant anaerobic metabolism, decrease in blood pH is countered by stimulation of ventilation to increase CO2 excretion, such that 
E increases at a higher rate than 
O2, raising the ventilatory equivalent (for CO2 the ventilatory equivalent, 
E/
CO2, increases in this instance less than that for O2 because as CO2 in the blood and lungs decreases, the same output is achieved by a smaller expired volume).
ventilatory threshold see metabolic and related thresholds.
ventral at or towards the front of the body; applies to the front of the hands and arms in the anatomical position when the palms face forwards. Opposite of dorsal.
ventricles the paired major chambers and muscular pumps of the heart. The left ventricle receives oxygenated blood from the lungs via the left atrium, and in an average-sized person at rest ejects a stroke volume of around 70 mL at each beat (contraction, systole) into the aorta, increasing during exercise by virtue of greater filling and stretching during each relaxation (diastole); the right ventricle receives venous blood from the rest of the body via the right atrium, and ejects the same volume as the left ventricle, in synchrony with it. The heart beat can normally be felt over the apex of the left ventricle. See appendix 1.3 fig 1.
vertebral column syn back bone, spinal column the dorsal axis of the body in all vertebrates. A bony and ligamentous structure extending from the uppermost (atlas) vertebra which articulates with the base of the skull, and ending above and behind the anus. Consists of 24 separate vertebrae linked by joints and by the intervertebral discs (seven cervical, 12 thoracic, which give attachment to the ribs, and five lumbar), plus five fused to form the sacrum (articulating with the ilium of the pelvic bones) and four rudimentary ‘tail’ vertebrae fused in the coccyx. Allows a limited amount of movement of the trunk and provides a protected tunnel, the vertebral (spinal) canal, for the spinal cord and the paired anterior and posterior spinal nerve roots, which leave through openings (intervertebral foramina) at the sides of the column, each being numbered according to that of the vertebra above the foramen. See also cervical spine, intervertebral discs, spinal injury; appendix 1.2 figs 1, 2.
vestibular apparatus sensory organs of the inner ear: the otolith organs and the semicircular canals. They detect tilt of the head with respect to the ground, and the direction and rate of any acceleration of the head in space. This input interacts with sensory information from muscles and joints, eyes and ears to co-ordinate reflex postural adjustments.
vicarious experience knowledge or information about a skill or behaviour derived from seeing the performance of others.
video analysis the use of video cameras and equipment to analyse motion, often for kinematic analysis.
viruses microscopic particles that can replicate only within a living animal or plant cell, so widely considered not to be themselves truly ‘living’, and not possible to destroy directly without also destroying the host cells. For those that cause human diseases, antiviral drug treatment is limited (antibiotics have no effect) but vaccination can provide immunity and in the second half of the 20th century this eradicated smallpox worldwide and much reduced the incidence of poliomyelitis. Viral conditions include colds, influenza, chickenpox, measles, hepatitis and herpes of different types (e.g. cold sores, shingles). See also human immunodeficiency virus (HIV).
visceral pertaining to the viscera or internal organs. Hence visceral afferents the components of the peripheral nervous system that carry information from the organs. The outgoing nerves to the viscera are the sympathetic and parasympathetic nerves of the autonomic nervous system but are not usually known as visceral efferents.
viscosity the property of a fluid medium that provides resistance to motion of the fluid itself or of an object moving through it. Also can be considered to be friction within fluids.
vital capacity the volume of air that can be inspired with maximal effort after forcefully emptying the lungs, or expired from full lung volume. See also lung volumes.
vitamins organic substances that are necessary in the diet, in very small quantities, for normal growth and health: the recommended daily allowance (RDA) for any vitamin, widely quoted on food and drink labels, is less than 200 mg. Originally identified by alleviation of conditions caused by their deficiency (e.g. of scurvy in ships’ crews in the 1750s by providing citrus fruit, the vital component being found later to be ascorbic acid, vitamin C). Nowadays hypovitaminosis due to lack of one or more vitamins is rare on a well-balanced diet, although occasionally an athlete may suffer from a deficiency, e.g. if dieting for weight loss or eliminating particular foods or food groups from the diet. hypervitaminosis can occur with excessive intake of one or more vitamins. The International Olympic Committee states that no vitamin supplements should be required if the diet is well balanced but athletes do often take them, especially vitamins C, B-complex and E, with a possible danger to their health by overconsumption. For sources, functions and deficiency effects, see appendix 4.2.
volitional behaviour in the theory of reasoned action, behaviour that a person intentionally enacts and that has no barriers or obstacles that would impede its enactment.
volume the amount of space taken up by an object or fluid. Expressed as cubic metres (m3). The more commonly used litre (L or l) and it subdivisions are not SI units, but accepted for use with them: 1 L = 1 cubic decimetre (1 dm3)= 103 m3.
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