G
gait style of locomotion, usually referring to walking or running. See also step length, stride, support, swing.
gamekeeper’s thumb see skier’s thumb.
gamesmanship in sport, the use of unfair tactics or methods, which are not strictly against the rules of the sport, in order to obtain an advantage over one’s opponent(s), such as feigning injury or engaging in other time-wasting strategies in order to delay the game.
gamma-(γ)-aminobutyric acid (GABA) inhibitory neurotransmitter in the central nervous system, with a general calming effect, promoting relaxation.
gamma (motor) system the component of the motor nerve outflow from the spinal cord which innervates ‘intrafusal’ muscle fibres (the fibres within muscle spindles). The gamma (γ) motor neurons have smaller cell bodies and narrower-diameter axons than alpha (α) motor neurons, which innervate the main working fibres of the muscle (extrafusal fibres).
ganglion (1) in anatomy: a small mass of nerve cells, outside the central nervous system, where synaptic connections relay afferent or efferent nerve impulses. ganglia pl. dorsal root ganglia contain the cell bodies of sensory neurons, providing relay into the spinal cord, and there are equivalent afferent relays to the brain stem for sensory components of cranial nerves. autonomic ganglia provide efferent relay from nerve fibres from the central nervous system to the sympathetic and parasympathetic neurons that innervate relevant tissues throughout the body; (2) in pathology: a fluid-filled fibrous tissue sac that develops on a tendon sheath, especially around the wrist. A ganglion is usually painless but they can increase in size to become tender, unsightly or large enough to restrict movement; treatment is not usually required but they can be surgically removed if troublesome.
gas exchange in the animal kingdom, the uptake of oxygen and excretion of carbon dioxide, exchanged between the body and the environment aka respiratory gas exchange. In human physiology pulmonary gas exchange refers to the diffusion of oxygen from the gas phase in the lung alveoli, through the thin alveolar-capillary membrane, into solution in the pulmonary capillary blood, and of carbon dioxide in the opposite direction, both driven by partial pressure gradients. See also blood gases.
gastric adj referring to the stomach.
gastrocnemius the most superficial of the muscles of the back of the lower leg. It arises from the medial and lateral femoral condyles by two heads which join to form the inferior border of the popliteal fossa behind the knee. Together with its smaller accessory, the plantaris, and the soleus muscle (arising from the shaft of the tibia), it converges onto the Achilles tendon, to be inserted into the middle of the back of the calcaneum. It acts to plantarflex the foot and raise the heel when walking. Gastrocnemius and plantaris also act as weak flexors at the knee. See appendix 1.2 fig 6B.
gender (1) in general use, synonym for biological sex; (2) the socially constructed views of feminine and masculine behaviour within individual cultural groups. gender identity a person’s sense of their biological sex. gender role the set of behaviours, attitudes and other characteristics normally associated with masculinity and femininity within a given culture or social group; for example, certain sports are stereotypically viewed as reflecting a masculine role (e.g. basketball) whereas others reflect a feminine role (e.g. netball).
general adaptation syndrome (GAS) the three-phase physiological response of the body to a stressor described in 1952 by the endocrinologist Hans Selye, of the University of Montreal. Comprises alarm, resistance/adaptation and exhaustion. The alarm phase is the short-term immediate response involving activation of the sympathetic nervous system. The resistance/adaptation phase involves the activation of the body’s defences against the stressor. If the stressor continues and cannot be adapted to, the exhaustion phase ensues in which resistance to the stressor and ability to resist disease collapses.
genes agents of heredity, each located at a specific site as part of the DNA macromolecule of a specific chromosome, in the nucleus of body cells. genotype an individual’s complete genetic endowment (specific genome) in the form of DNA, which largely, but not entirely, determines the individual’s unique characteristics, known as the phenotype. See also performance genes.
gene therapy see performance genes.
genetic potential theoretical optimum performance capability which an individual could achieve in a specific activity, after an ideal upbringing, nutrition and training. In real terms it may be assumed that the finalists in a world championship are among the human beings whose performance comes closest to their genetic potential. Also known as genetic endowment. See also performance genes.
genetic profiling see performance genes.
genu valgum (bow legs) abnormal outward curving of the legs resulting in separation of the knees. Associated with hypermobility. See also genu varum.
genu varum (knock knee) abnormal incurving of the legs so that there is a gap between the feet when the knees are in contact. Associated with hypermobility. See also genu valgum.
ginseng name commonly used for several species of Panax herbs. A naturally occurring substance, not banned in sport, ginseng has been suggested to have performance-enhancing properties, though these have not been scientifically proven. In addition, several preparations of ginseng have been found to be contaminated with banned substances. Side effects include insomnia, depression and high blood pressure.
gland an organ or structure whose cells produce a secretion: exocrine, delivered via ducts to the skin surface or an internal surface, e.g. in the gut, or endocrine, passed into the blood stream. See also digestion, hormones, sweating.
Glasgow Coma Scale (GCS) reliable and universally recognized method for assessment of conscious level following head injury (described by neurosurgeons Teasdale & Jennett 1974). Three types of response are measured: best motor response (score 1–6), best verbal response (score 1–5) and eye opening (score 1–4). The lowest score is 3 (1 in each category). A GCS of 8 or less indicates severe injury, 9–12 moderate injury and 13–15 a mild injury.
glucagon polypeptide hormone secreted by alpha cells of the islets of Langerhans in the pancreas. Secretion is stimulated by a decrease in blood glucose level. It elevates blood glucose by promoting glycogenolysis and gluconeogenesis in the liver and also mobilizes free fatty acids from adipose tissue, having opposite actions at these sites to those of insulin. The ratio of insulin to glucagon secretion appropriately decreases in exercise.
glucocorticoids the group of corticosteroid hormones (mainly cortisol syn hydrocortisone, of which cortisone is the precursor) produced by the adrenal cortex, under the control of adrenocorticotrophic hormone (ACTH) from the anterior pituitary. Their major actions on nutrient metabolism have the net effect of promoting glucose and free fatty acid availability as fuels. Also vital for normal cellular processes as diverse, for example, as excitation–contraction coupling and the health of connective tissues. Synthetic steroids such as prednisolone and dexamethasone have similar actions and are used in the treatment of, for example, asthma and rheumatic conditions. Banned in sport due to their powerful anti-inflammatory action and effect of producing euphoria and masking pain. (Not to be confused with anabolic steroids). See also adrenal glands, hormones; appendix 5.
gluconeogenesis synthesis of glucose from non-carbohydrate precursors mainly in the liver and to a smaller extent in the renal cortex. Precursors include pyruvate, lactate, glycerol and the glucogenic amino acids derived from skeletal muscle. The glucose-alanine cycle involves the conversion of alanine, formed in muscle, to glucose in the liver; activity of the cycle is increased during the postabsorptive state and in starvation or prolonged exercise, slowly mobilizing glycogen stores and using protein for the maintenance of normal blood glucose concentration. Gluconeogenesis and export of glucose from the liver are promoted by the hormone glucagon, and inhibited by insulin.
glucose a hexose (monosaccharide) found in certain foods, and in the circulating blood and cells of all animals; of major importance as a source of energy in all tissues, and essential for some. Ingestion of carbohydrates provides glucose for replenishment and for accumulation of liver and muscle glycogen. When there is overconsumption of carbohydrate, excess glucose is used in the formation of triglycerides which are stored in adipose tissue. Glucose metabolism is mainly controlled by the hormones insulin and glucagon. The glucocorticoid hormones from the adrenal cortex and growth hormone from the anterior pituitary are also involved. See also blood glucose.
glucose-electrolyte drinks see sports drinks.
glucose transporters a family of membrane proteins that transport glucose across cell membranes down its concentration gradient, into most cells but out of the liver and kidney cells when gluconeogenesis occurs.
glutamine the amide of amino acid glutamate, synthesized in skeletal muscle. Glutamine is one of the major fuels of the gut lining, and of the cells of the immune system. It is also a precursor for the gluconeogenesis that occurs in the kidneys after an overnight fast or in starvation. Glutamine supplementation is popular among athletes attempting to maintain a healthy immune system during training. See also glucogenic amino acids, ergogenic aids; appendix 4.4.
gluteal muscles see buttocks; appendix 1.2 figs 4A, 6B.
glycaemic index (GI) a ranking of foods based on the extent and rate of the postprandial rise in blood glucose that they cause, compared to the response to a reference food (either glucose or white bread); the higher the GI, the greater and more rapid the rise. Intake of carbohydrate (CHO)-rich foods with lower GI has been shown to be beneficial in improving glucose control, particularly in people with type 2 diabetes. Consideration of GI may also be relevant to athletic performance. High-index CHO-rich meals have been reported to enhance the storage of muscle glycogen during recovery from prolonged exercise. On the other hand, some evidence favours consumption prior to exercise of low rather than high GI CHO-rich foods, since high GI may elicit an inappropriate surge of insulin and/or attentuate fat oxidation, leading to faster depletion of glycogen and onset of fatigue. See also carbohydrate intake guidelines for athletes.
glycerol three-carbon carbohydrate; known as the ‘backbone of triacylglycerol’. Blood glycerol concentration mainly depends on the rate of lipolysis of triglycerides in adipose tissue. Glycerol is an important source of glucose during periods of fasting or starvation. In sport, consumption of glycerol may be used for hyperhydration, as it reduces renal water clearance, increasing fluid retention and total body water. See also gluconeogenesis, hydration status.
glycogen branched polysaccharide formed of glucose subunits. Glycogen accumulation in liver and skeletal muscle is the principal way of storing ingested carbohydrate. The liver normally contains ∼100 g (energy value 400 kcal) and skeletal muscle ∼400 g (1600 kcal) of glycogen. It is also stored in the brain. The body’s upper limit for glycogen storage is ∼1050 g. It is known that aerobic endurance performance is directly related to the initial muscle glycogen and that perception of fatigue during prolonged exercise parallels the decline in these stores. See also carbohydrate, carbohydrate loading, glycogenesis.
glycogen loading see carbohydrate loading.
glycogenesis the formation of glycogen from glucose by the action of the enzyme glycogen synthetase in liver and muscle. Very active after depletion of muscle glycogen in exercise, making rapid restoration possible, provided that there is adequate consumption of carbohydrates. Even more ample carbohydrate supply can allow glycogen supercompensation – elevation in muscle glycogen content above normal. See also carbohydrate loading.
glycogenolysis removal of a glucose molecule from glycogen, by the action of the enzyme glycogen phosphorylase, present in liver, kidneys, muscle and brain. The products are a glycogen molecule that is one glucose residue shorter than before and glucose-1-phosphate. This in turn is converted to glucose-6-phosphate, from which free glucose can be released from the liver and kidneys (but not from skeletal muscle or brain) by the action of glucose-6-phosphatase. See also glucose, glycolysis.
glycolysis a catabolic pathway that breaks down glucose 6-phosphate, derived from glucose or glycogen, and in the process generates energy which leads to production of ATP. In aerobic conditions, pyruvate is the end-product. In conditions when oxygen cannot be utilized anaerobic glycolysis involves the additional step of reducing pyruvate to lactate. See also aerobic exercise, anaerobic exercise.
goal orientation see achievement goal orientation, task orientation, ego orientation.
golfer’s elbow also known as medial epicondylitis or javelin thrower’s elbow. An inflammatory condition affecting the common origin of the flexor tendons of the forearm which results in pain and tenderness on the inside (ulnar side) of the elbow at the medial epicondyle of the humerus. Most commonly the result of overactivity of the wrist flexors, especially with increasing intensity or duration of activity or poor technique. Treatment includes rest, anti-inflammatory medication, physiotherapy and corticosteroid injection. Prevention of recurrence depends on identifying training or technique errors which can be corrected.
golfer’s toe an inflammatory condition of the big toe, which is thought to be the result of overextension of the toe of the back foot on the follow-through. Continued overuse can lead to arthritis.
Golgi tendon organs tension sensors in tendons that send afferent impulses to the central nervous system, causing reflex inhibition to counterbalance whatever neural influences, voluntary and reflex, are stimulating the contraction. Thus they guard against excessive tension generation (with potential tearing of muscle or tendon). In less extreme circumstances, which are more common and probably more important, tendon organs interact with muscle spindles to control limb stiffness. First described in 1898 by Camillo Golgi, Italian histologist and Nobel prize winner.
gonad organ that produces the gametes (germ cells): ovary and testis.
gonadotrophins hormones secreted by the anterior pituitary, under the influence of the hypothalamus, which control the development and secretory function of the ovaries and testes. In pregnancy, ovarian function is under the influence of the placental secretion of human chorionic gonadotrophin (HCG), which also acts on the fetal testis. See also hormones; appendix 5.
goniometer a protractor-like device, commonly with a 180° range, used to measure a joint’s position when stationary, at any point over its whole range of movement. Used in practice to assess flexibility, perhaps as part of a musculoskeletal screen.
graded exercise test used to assess physiological responses to exercise, with its intensity increasing in incremental stages. See also exercise stress test.
gravitation, law of relates the attraction between two bodies or objects to their masses and the distance between their centres of gravity squared. First proposed by Isaac Newton.
gravitational acceleration acceleration caused by the gravi tational attraction between two bodies or objects which depends on their masses and the distance between them squared.
gravitational potential energy the energy due to the position of a body or object in a gravitational field. Often calculated as weight multiplied by vertical height above some base (arbitrary) datum. Also known as potential energy.
gravity the force due to the attraction between two bodies or objects which depends on the product of their masses and inversely on the square of the distance between their centres of gravity.
greenstick fracture a fracture where the bone does not break completely, is essentially intact, but splinters like a ‘green stick’. Occurs in children due to the flexibility of immature bone, commonly in sport with a fall on an outstretched arm.
grip dynamometer instrument for measuring the maximum isometric force with which an individual can squeeze two handles together between palm and fingers. Also known as handgrip dynamometer.
groin pain is most common in dynamic sports where quick turns are made, such as football, martial arts and skiing. The cause can be difficult to identify. Sporting causes include strains of the muscles in the area (e.g. the adductors, gluteal muscles, iliopsoas), bursitis, osteitis pubis and hernias. Abduction of the leg against resistance is restricted by pain. Because there are more serious causes of groin pain, a full clinical examination must be carried out if the pain is persistent. Treatment can be difficult and requires a formal rehabilitation programme to prevent a chronic condition. See also groin strain.
groin strain an injury which results from overstretching of the adductors in the groin, especially common in football. Requires a rehabilitation programme for both flexibility and strengthening. See also groin pain.
ground reaction force see force plate.
group cohesion a group’s tendency to stick together in its pursuit of common goals. Also known as team cohesion.
group dynamics the ongoing social interactions and processes within a group.
group environment the task-related or social aspects of a group that can facilitate or undermine group cohesion.
group integration the beliefs that individual group members hold about the cohesiveness of the group as a whole.
group therapy any of various forms of psychotherapy in which individuals are treated together in groups.
growth curve a graph of change-in-height against age, which shows the greatest rate of change in infancy, flattening off until the growth spurt which on average reaches a peak at about age 12 in girls and 14 in boys.
growth hormone (GH) aka human growth hormone (HGH), somatotrophin. Hormone secreted by the anterior pituitary under the control of GH releasing hormone (GH-RH) and GH release-inhibiting hormone (GH-RIH) (aka somatostatin) from the hypothalamus. As well as being vital for normal growth and development (e.g. stimulates the growth of the long bones), GH is involved throughout life in metabolism and utilization of all the macronutrients, e.g. it increases protein synthesis and raises blood glucose level. GH acts directly on some body cells (e.g. on adipocytes, promoting triglyceride breakdown) but mostly indirectly, via the anabolic insulin-like growth factors (IGF) syn somatomedins which it causes the liver and other tissues to release, crucial, for example, for the muscle hypertrophy resulting from training. For this reason supplements rich in arginine, which is believed (but without conclusive evidence) to promote GH secretion, are frequently taken by body builders. Any exercise of sufficient intensity stimulates GH release; its level in the blood has been shown to rise within the first 15 minutes and it is important throughout in maintaining lipolysis and lipid metabolism. Synthetic GH is commercially available, but banned in sport.
gumshield see protective equipment.
gymnast’s back injury to the back, including fractures, due to excessive hyperextension during gymnastic activity.
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