C
caffeine occurs naturally in the leaves, seeds or fruits of more than 60 different plants, including coffee beans, kola nuts (cola) and tea leaves, and is also added to some foods and soft drinks; there is also a closely related substance in cocoa beans (chocolate). Caffeine is often said to be the most widely used drug in the world. It is one of the commonest ingredients in fat-loss supplements; it can help relieve some types of headache, so is an ingredient in a number of pain relievers. By virtue of its stimulant action in the brain, it is used in sport to improve alertness, concentration and reaction time and to delay central fatigue. By promoting lipolysis, and therefore fat oxidation, caffeine acts as an aid to endurance but its diuretic action may enhance fluid loss and thus reduce hydration. See also ergogenic aids, fatigue, lipolysis, methylxanthines; appendix 4.4.
calcaneum (calcaneus) the heel bone which articulates with the talus above it and the cuboid bone in front. The Achilles tendon attaches to the back of the calcaneum. See also foot; appendix 1.2 figs 1-3.
calcium the most abundant mineral in the body. Combined with phosphorus in bones and teeth. The two together represent about 75% of the body’s total mineral content. ionized calcium ( Ca2+), about 1% of the 1200 mg total calcium, plays a crucial role in all physiological functions including muscle action, blood clotting, transmission of nerve impulses, activation of several enzymes, synthesis of the active form of vitamin D, and transport across all cell membranes; its level in the blood is regulated by exchange with Ca in bone and by variation in renal excretion, under hormonal influences. Calcium is one of the most frequently inadequate nutrients in the diet of both athletes and non-athletes. Female dancers, gymnasts and endurance competitors are among those most prone to calcium dietary insufficiency. See also bone, coagulation, excitation-contraction coupling, hormones (table appendix 5), micronutrients, minerals, parathyroid gland, tetany.
calcium (Ca) pump one of many similar molecular complexes embodying ion-binding sites and an ATPase in the surface membrane of many cell types, including smooth and cardiac muscle, and in the membrane of the sarcoplasmic reticulum (SR) in skeletal muscle. The pumps actively transport calcium ions (Ca2+) out of the cytoplasm; those in the surface membrane return them to the extracellular fluid, and those in SR membrane return them to within the SR. All use energy derived from hydrolysis of ATP.
calculus the use of small changes to calculate derivatives of equations. Includes differentiation (calculation of gradients) and integration (calculation of areas). Invented in the 17th century by Newton and Leibnitz independently.
calf the twin ‘bellies’ of the gastrocnemius are prominent in the upper half of the calf, e.g. when standing on tip-toe; this and the flatter soleus in front of it (known together as the triceps surae) form the main bulk of the calf muscles; their tendons join to attach to the calcaneum via the Achilles tendon. Accessory to the gastrocnemius is the plantaris. Deeper muscles include the flexors of the toes, with long tendons passing into the foot. See appendix 1.2 fig 6B.
callus the collagenous tissue which forms around a healing bone at the site of injury.
calorie a unit of energy, defined as the energy in the form of heat that will raise the temperature of 1 gram of water by 1 degree Celsius. Values are more often quoted in kcal (kilocalories): 1 kcal = 1000 calories = 4.2 kJ. In food, 1 g of carbohydrate or protein provides about 4 kcal and 1 g of fat, 9 kcal of energy. Energy is also provided by alcohol, at 7 kcal per gram. calorie restriction is the commonest treatment of obesity and overweight: an essential part of any weight control programme. Obsession with weight loss may result in disordered eating. See also anorexia, bulimia.
calorimetry technique used for the measurement of energy expenditure. direct calorimetry evaluates energy expended over a given time by measuring heat emitted from the body. Heat loss is detected by using room-sized chambers. indirect calorimetry when foods are oxidized in the body, oxygen is used and carbon dioxide is produced in proportion to the heat generated. Energy expended over a given time can be estimated from oxygen consumption alone. For greater accuracy and information about the relative amounts of nutrients (carbohydrate, fat and protein) oxidized, carbon dioxide production is also measured and urea production estimated. See also Douglas bag method.
capsule the fibrous tissue that covers a joint. Inflammation of this tissue is known as capsulitis.
carbohydrate (CHO) the most abundant and economic source of food energy in the human diet, comprising 40–80% of total energy intake in different populations. The recommended ideal is at least 50–55% and a high-carbohydrate diet is defined as one providing more than 55% of energy as CHO. Contained in breads, cereals, fruits, vegetables, milk and dairy products, soft drinks, cakes, biscuits and pastry. One gram of CHO provides ∼4 kcal of energy. In Western diets about 60% of dietary CHO is in the form of polysaccharides of D-glucose, mostly starch, and about 25% ‘free sugars’, mainly sucrose. The quantity and quality of carbohydrate consumed have impact on energy balance, digestive function, insulin sensitivity and blood lipids. CHO is present in the blood as glucose and carbohydrate stores are in the form of glycogen in the liver and skeletal muscle and to a small extent in other tissues including, importantly, the brain. See also glycaemic index; appendix 4.
carbohydrate intake guidelines for athletes the IOC suggests that athletes with considerable and prolonged energy demands of training should have a high-carbohydrate diet, increasing CHO intake to 65–70% of dietary energy. However, due to the high total energy intake of athletes, population dietary guidelines that recommend a CHO component of at least 50–55% are in most cases appropriate also for the health needs and fuel requirements of athletes. For athletes, therefore, the recommended CHO intake is usually expressed in grams per day or grams per day per kg body mass, rather than as a percentage of the total.
Carbohydrate intake guidelines for athletes
| Purpose | Intake per kg body mass | Intake for body mass of 70 kg |
|---|---|---|
| To accumulate muscle glycogen for endurance events of 1–3 hours at moderate to high intensity | 7–10 g daily | 490–700 g daily |
| To accumulate muscle glycogen for endurance events of 4–5 hours at moderate to high intensity | 10–12 g daily | 700–840 g daily |
| To increase availability before a long session | 1–4 g within 4 hours of start | 70–280 g within 4 hours of start |
| To maintain CHO supply during moderate or intermittent exercise lasting longer than 1 hour | 0.5–1.0 g hourly | 40–70 g hourly |
| To assist recovery of muscle glycogen, when interval between exercise sessions is only a few hours | 1 g immediately after exercise, repeated after 2 hours | 70 g repeated |
carbohydrate-electrolyte solutions see sports drinks.
carbohydrate loading aims to maximize (supercompensate) muscle glycogen stores. This allows athletes to maintain a chosen pace for longer periods and also enhances the performance of a set amount of work (i.e. set distance) by preventing a decline in pace or work output associated with CHO depletion. The procedure is popular with long-distance runners and other endurance-type athletes; it is an important nutritional strategy for events lasting more than 90 minutes, which would otherwise be limited by the depletion of muscle glycogen stores. In practice, loading is performed in two stages: a glycogen depletion stage and a carbohydrate loading phase, typically spread over 6–7 days, which entail a few days of minimal CHO intake with initially high but then decreasing intensity of training, followed by a few days of high CHO diet and minimal exercise.
cardiac arrest cessation of the heart beat. See also cardiopulmonary resuscitation (CPR), sudden death.
cardiac arrhythmias see arrhythmia.
cardiac cycle the events in the heart over the period from the beginning of the generation of one heart beat to the beginning of the next. The electrical cycle begins with discharge from the sinoatrial node, spreading excitation through the atrial muscle then via the atrioventricular node to the ventricular muscle; after this an isoelectric phase precedes the next cycle. The mechanical cycle begins with simultaneous contraction of the right and left atria (assisting filling of the ventricles); contraction of the ventricles (systole), raising pressure within them, which closes the atrioventricular and opens the aortic and pulmonary valves; ejection of blood; then relaxation (diastole) and refilling. See also blood pressure, cardiac output, electrocardiogram (ECG).
cardiac hypertrophy thickening of the myocardium, particularly the left ventricle. This may occur physiologically as a result of athletic training and is usually a uniform increase in thickness of the ventricular wall. Pathologically it may be the result of hypertension, secondary to outflow tract obstruction (e.g. aortic valve stenosis) or to congenital abnormalities. See also athlete’s heart, hypertrophic obstructive cardiomyopathy (HOCM).
cardiac massage performed to restore/maintain circulation when there is cardiac arrest. For external cardiac massage the lower part of the sternum (breastbone) is rhythmically depressed to compress the heart and force out blood into the arteries. More drastically, the chest may be opened, to allow direct manual compression of the heart. See also cardiopulmonary resuscitation (CPR).
cardiac output (CO) the volume of blood ejected per minute from each ventricle of the heart simultaneously, i.e. to the lungs via the pulmonary artery, and to the rest of the body via the aorta (although often defined solely as the output from the left ventricle). The product of stroke volume (SV) and heart rate (HR): at rest, e.g. 70 mL × 70 per minute = 4.9 L.min−1(4–6 L.min−1 varying with body size). Increase in CO in exercise involves increase in heart rate, accompanied by greater filling during diastole (by increased venous return to the heart), maintaining then increasing stroke volume, due to stretch of the ventricular muscle and to enhanced contractility from sympathetic stimulation; also the residual volume remaining in the ventricles after ejection decreases. Maximal CO in exercise increases with athletic training (by hypertrophy of ventricular muscle, with raised SV and lowered HR at rest, allowing a greater increase) exceptionally up to SV 200 mL × HR 200 = 40 L.min−1, but a more modest maximum is typical.
cardiac rehabilitation a structured, planned programme, originally restricted to patients following myocardial infarction, designed to achieve and maintain the maximum degree of physical and psychological independence of which they are capable. Now extended to include all patients with any cardiovascular disease. The programme is exercise based, with a gradual increase in activity individually tailored to suit clinical status and level of symptoms. Educational (risk factor modification) and nutritional sessions are included for both patient and spouse/partner and the psychosocial aspects such as return to work, resumption of sexual intercourse, etc. are covered.
cardiomyopathy a group of diseases of the myocardium associated with cardiac dysfunction. It is classified as dilated, hypertrophic or restrictive. Management includes treatment of the cause (if possible) and treatment of heart failure. Heart transplantation is sometimes required. See also hypertrophic obstructive cardiomyopathy (HOCM), sudden death.
cardiopulmonary resuscitation (CPR) the techniques used to restore and maintain the circulation and ventilation of the lungs following cardiopulmonary arrest. Involves (a) opening and clearing the airway; (b) artificial ventilation (artificial respiration), mouth-to-mouth or mouth-to-nose, using a bag and face mask, or via an endotracheal tube; (c) external cardiac massage.
carnitine (L-carnitine) a short-chain nitrogen-containing carboxylic acid, mainly located in skeletal and cardiac muscle cells. Over half the daily requirement is provided from meat and dairy products in a balanced diet; the remainder is synthesized in the liver. It has been hypothesized that supplementary ingestion of L-carnitine might upregulate the capacity to transport fatty acids into mitochondria matrix where they are metabolized and so increase their oxidation, thus benefiting both endurance athletes and those wishing to reduce their body fat. Research has not supported these claims. See also ergogenic aids; appendix 4.4.
carotid arteries the principal arteries on each side of the neck, providing a major part of the blood supply to the head and neck. Where each common carotid artery divides into external and internal branches, there is a dilatation, the carotid sinus; nerve endings in its walls (baroreceptors) are sensitive to stretch caused by rising arterial blood pressure, and via connections to the brain stem lead to reflex slowing of the heart rate and thus a corrective fall in pressure (baroreflex). The internal carotid artery enters the base of the skull to reach the brain; the external carotid artery provides branches that supply the extracranial tissues of the head and neck. See appendix 1.3 fig 2.
carotid bodies small clumps of tissue close to the carotid arteries, containing chemoreceptors that respond rapidly to a fall in oxygen, decrease in pH and/or increase in carbon dioxide in the arterial blood. Via neural connections to the brain stem, they mediate reflex responses (chemoreflexes) including an increase in ventilation, which correct or compensate for these changes. See also hypoxia.
carpal bones see scaphoid bone, wrist, wrist joint.
carpal tunnel syndrome nocturnal pain, numbness, weakness of the thumb and tingling in the area of distribution of the median nerve in the hand. Due to compression of the nerve as it passes under the fascial band on the front of the wrist. Most common in middle-aged women.
Cartesian co-ordinate system see co-ordinates.
cartilage a dense connective tissue capable of withstanding pressure. There are several types according to the function each has to fulfil. There is relatively more cartilage in a child’s skeleton but much of it has been converted into bone by adulthood. cartilaginous adj. See also knee joint, meniscus.
catastrophe theory a set of mathematical theorems employed in the modelling of discontinuities in the physical world, that result when gradually changing and interacting variables reach a critical point. Applied in sportpsychology to the understanding of sudden decrements or increments in performance, incorporating changes in cognitive anxiety, physiological arousal and self-confidence.
catecholamines substances that mediate the effects of activity of the sympathetic nervous system. Released into the blood as hormones from the adrenal medulla, and act as neurotransmitters at sympathetic nerve endings and within the central nervous system. The main ones are adrenaline (epinephrine), noradrenaline (norepinephrine) and dopamine. See also adrenoceptors, hormones; appendix 5.
cauliflower ear colloquial term for an auricular haematoma – a collection of blood within the pinna (external ear). Usually the result of trauma, especially common in boxing and rugby. The close adherence of the skin to the underlying cartilage of the pinna leads to painful stretching of the tissue, which may need surgical drainage and pressure to prevent further accumulation and later deformity.
causality see locus of causality.
cell the basic structural unit of living organisms. A human body would typically have ∼1014 cells of different types, ranging in diameter from about 1 to 100 microns. The outer cell membrane (syn plasma membrane) is a double layer of lipid with embedded protein molecules. These include: molecules that embody enzymes involved in transport across the membrane; receptor molecules which selectively bind hormones, drugs and other agents, mediating their signal to the cell; and others with water-filled pores that allow exchange across the cell membrane of water, ions and small molecules, related to concentration and electrical gradients. The enclosed cytoplasm contains the intracellular fluid and a great number and variety of structures, some surrounded by their own membrane, including the nucleus containing the chromosomes that carry the genes, and mitochondria in all cells where oxidative metabolism occurs. See also membrane potential, potassium, sodium, sodium-potassium (Na-K) pump.
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