H
habit (1) a tendency to behave in a certain way; (2) a well-learned behavioural response associated with a particular stimulus or situation, typically evoked without conscious intention.
habituation the reduction in the strength or frequency of a response to a stimulus due to repeated exposure to the stimulus.
haemarthrosis the presence of blood in a joint cavity. This may be the result of trauma or occur spontaneously, as in haemophilia. In sport haemarthrosis is most commonly seen in the knee joint where it is always indicative of significant injury such as cruciate (70% have an anterior cruciate tear) and/or collateral ligament injury, intra-articular fractures, meniscal tears or patellar dislocation. Blood accumulates in the joint within 1–2 h in a haemarthrosis compared to the slower (24+h) accumulation in a joint effusion. Early referral to a knee specialist is recommended because of the potential for intervention to prevent chronic joint damage.
haematocrit the proportion by volume of blood occupied by erythrocytes (red blood cells, RBC): on average 45%, i.e. 45 mL of red cells in 100 mL of whole blood. Exercise-induced increase in haematocrit, together with measurement of haemoglobin concentration, allows estimation of change in plasma volume. Also known as packed cell volume (PCV). See also altitude acclimatization.
haematoma a swelling, composed of extravasated blood, which is usually traumatic in origin. One of the most common injuries in sport and one which benefits from early treatment with ice, compression and elevation.
haemoconcentration decrease in the volume of plasma relative to the volume of cells in the blood (increase in haematocrit). Consequence of dehydration.
haemoglobin the iron-containing protein with the property of binding oxygen, contained in red blood cells. See also oxyhaemoglobin dissociation curve.
haemophilias a group of inherited conditions in which blood coagulation is defective, resulting in an increased tendency to bleed, both spontaneously and as a result of trauma. For this reason, participation in contact sport is not advised.
haemopoiesis see bone, erythrocytes, erythropoiesis, leucocytes.
haemorrhage loss of blood from a ruptured blood vessel. In sport, usually the result of trauma. Significant bleeding may result from either an externally obvious injury (e.g. fractured tibia, lacerations) or less obvious internal trauma (e.g. ruptured spleen, lung trauma) and may result in shock. See also shock.
haemothorax a collection of blood in the pleural cavity around the lung(s).
hallux the first, great or big toe. hallux rigidus is a stiff and painful toe resulting from osteoarthritis of the metatarsophalangeal joint. In hallux valgus the toe bends at this joint towards the second toe, and the joint bulges from the side of the foot. Can result in permanent displacement (possibly with a degree of external rotation) greater than 10%. Additional friction from poorly fitting footwear can result in a bursa, and the prominence of bone-plus-bursa is known as a bunion.
hamstring muscles the group that forms the bulk of the back of the thigh, made up of three muscles: semimembranosus, semitendinosus and biceps femoris; their tendons cross behind both the hip and the knee joints, so their action is to extend the hip and flex the knee. Their function is important in standing, walking and running and therefore vital in sport. Injury is common in sport, especially where sprinting or sudden acceleration is required when the muscles are under greatest tension, and is usually felt as a sudden sharp pain in the back of the thigh. hamstring strains are graded 1, 2 or 3 (complete rupture) depending on severity. Rehabilitation should include not only treatment of the soft tissue damage but also attempts to ascertain and where possible correct any underlying aetiological factors such as inadequate warm-up/stretching, poor low back flexibility and biomechanical abnormalities, e.g. an abnormally tilted pelvis. See appendix 1.2 fig 6B.
hand a complex musculoskeletal structure, allowing the complexity of movements required. The carpal bones at the wrist articulate with the five metacarpals, and each of these in turn with the first of the three phalanges of each digit. There are many small muscles attached between the various bones, which contribute to finger and thumb movements together with the long tendons of the forearm muscles which span the wrist in their tendon sheaths. hand injury is most common in sports such as basketball, rugby, cricket, volleyball, handball, etc. Injuries include ligament sprains, fractures and dislocations. See appendix 1.2 fig 1.
hand grip see grip dynamometer.
hardiness in a psychological context, a dispositional tendency comprising a cluster of attitudes, beliefs and behavioural and mental skills that are held to promote resilience to the negative effects of stress on health and well-being.
Harvard step test see step test.
Hawthorne effect an improvement in performance due to changes in environmental conditions regardless of the nature of the changes. Named after an electricity company’s plant in the US where a series of studies was conducted in the 1920s into the effects of variations in environmental conditions on workers’ performance and productivity. In experimental design the term is often used to describe a threat to validity whereby participants’ performance on a task improves due to them feeling that the experimenter shows concern for them.
head injury potentially the most serious injury in sport. Injury risk is greatest in contact sports (such as boxing, rugby, football and American football) or in sports which involve a fall from height (horse riding, trampolining, gymnastics) or movement at speed (cycling, motor sports). The risk of a head injury is brain damage via either internal bleeding or a shearing force. Management of head injuries in sport requires appropriately trained personnel who adhere to the relevant guidelines especially regarding referral to hospital and advisability or otherwise of return to play. See also amnesia, coma, concussion, Glasgow Coma Scale (GCS).
health education the provision of information to the public or individuals to reduce ill health and enhance positive health by influencing beliefs, attitudes and behaviour.
health promotion any initiatives, by any public or private agency, to prevent ill health and promote positive health through a variety of strategies ranging from the implementation of public health policies to encouraging individual changes in health behaviours.
heart four-chambered organ, receiving venous blood from the systemic circulation into the right atrium, passing it on to the right ventricle to be pumped through the lungs in the pulmonary circulation; oxygenated blood in the pulmonary veins enters the left atrium and thence to the left ventricle, to be pumped out in the aorta to all systemic arteries. Valves control the direction of flow. The myocardium (cardiac muscle) forms the walls of the chambers which are lined by the endocardium. The heart is contained within the membranous pericardium. See also cardiac cycle; appendix 1.3. See fig overleaf.
heart attack also known as myocardial infarction. Results from a sudden occlusion of one of the coronary arteries, which supply the heart muscle (myocardium). Usually due to the formation of thrombus (blood clot) at the site of a pre-existing narrowing of the artery (coronary thrombosis). Common symptoms include the sensation of tightness or heaviness in the chest, which can radiate to the arm or neck, breathlessness, sweating and nausea. Requires immediate hospital admission due to risk of cardiac arrest. In sport, this is the commonest cause of sudden death in those over 45 years. Risk factors include cigarette smoking, high blood pressure, obesity, physical inactivity and raised cholesterol levels. Exercise programmes are recommended in the prevention of heart disease and used in the rehabilitation of patients following a heart attack. See also cardiac rehabilitation.
heart failure the condition when the heart’s ability to pump blood around the body is diminished. Common causes include ischaemic heart disease, hypertension, disorders of the heart muscle or congenital heart disease. Symptoms include breathlessness (especially at night or on exertion) and leg swelling (oedema). Diagnosis is based on the history and clinical examination with additional investigations including a chest X-ray, ECG and echocardiography. Modern drug treatment starts with diuretics and ACE inhibitors. See also angiotensin, cardiomyopathy, coronary artery disease.
heart murmur a sound additional to the normal heart sounds, heard on auscultation of the heart. Many murmurs are of no significance (innocent, physiological murmurs), particularly in young children, or due to increased blood flow through the heart during exercise, or in pregnancy. pathological murmurs may be due to abnormalities in the heart’s structure or turbulent flow through a heart valve abnormality (congenital or acquired: in adults most commonly following rheumatic fever). Symptoms may include breathlessness, palpitations, chest pain or fainting but many murmurs are asymptomatic and are identified, for example, during routine medical examination. All sports participants found to have a murmur should undergo full cardiovascular assessment, including echocardiography, to exclude any cause which might increase the risk of sudden death during exercise. Management is of the underlying cause and surgery may be indicated in certain conditions, especially for significantly narrowed heart valves. See also heart sounds, medical screening.
heart rate (HR) the number of heart beats per minute, ranging typically from a resting heart rate of 60–75 (but can be less than 50, especially in trained endurance athletes) to a maximal heart rate in exercise that depends on fitness and age (average guide: 220 minus years of age). Regulated by the balance between sympathetic and parasympathetic influences on the pacemaker (sinoatrial node). See also cardiac output.
heart rate reserve (HRR) maximal minus resting heart rate (HRmax – HRrest): the Karvonen formula.
heart sounds The two sounds heard on listening to the heart with a stethoscope (auscultation) during normal cardiac contraction. The first (heard best at the apex) is due to the closure of the two atrioventricular valves (mitral and tricuspid); the second (heard best at the base of the heart) marks the closure of the aortic and pulmonary valves. Two components of the second sound can be heard separately (split heart sound) as a normal feature. Additional heart sounds (third or fourth) may be a sign of cardiac disease. See also cardiac cycle.
heat acclimatization the process of improvement in tolerance to heat as a result of repeated sessions of exercise in a hot environment, resulting in a measurable improvement in physiological response. The body’s response includes increase in the rate of sweating but decrease in sodium in the sweat, preserving salt by the action of aldosterone; increase in skin blood flow and overall control of body temperature as environmental conditions (air temperature and humidity) change. In addition, acclimatization will reduce the incidence and severity of heat illness. See also acclimation.
heat illness the term used to describe the spectrum of conditions which result from the effects of excessive heat, whilst hyperthermia refers to any elevation of the body (core) temperature above normal. Heat problems are influenced by humidity, which reduces heat loss by evaporation. Young children have less ability to lose heat by sweating and are therefore more susceptible. heat cramps muscle cramps with general fatigue that occur after exercise, associated with profuse sweating and the resulting salt loss. Treatment is removal from the hot environment, plus salt and water replacement. heat exhaustion is the most common heat illness in sport. Symptoms are often vague and include faintness, loss of co-ordination, profuse sweating, headache, nausea, dizziness and thirst. It is related to alterations in fluid/electrolyte balance and changes in blood volume. Treatment is removal from the hot environment, external cooling, elevation of the legs, fluid replacement and careful monitoring of airway, breathing and circulation (ABC). heat syncope occurs with postural pooling of blood and a decrease in venous return resulting in relative cerebral hypoperfusion. It occurs most commonly with a sudden rise in temperature or humidity. Salt and water depletion are less common than in the other types of heat illness. heat stroke is rare but can be fatal; it is at the end of the spectrum of heat illness when the body temperature continues to rise as heat loss by sweating fails due to dehydration; the result is collapse, possible seizures, coma and death. It is a medical emergency and should be treated as such with immediate admission to hospital.
hepatic pertaining to the liver.
hernia the abnormal protrusion of part of an internal organ through an aperture in the surrounding structures, most commonly part of the intestine through a defect in the abdominal wall musculature. Weakness of the muscle may be due to injury or previous surgery; obesity or heavy lifting add to the risk. If the protrusion becomes stuck in the narrow gap (incarcerated hernia) the blood supply may be compromised (strangulated hernia) and surgery is required. Common types of hernia include abdominal, femoral and inguinal. In sport the groin is a common site of pain or discomfort, and the term sportsman’s hernia is sometimes used inappropriately for a variety of other conditions that cause it (including musculotendinous injuries and osteitis of the pubic bone). It is important to diagnose accurately the cause of groin pain, as treatment options, including those involving surgery, will differ, and particularly relevant to identify a true hernia, which may be due to a tear in the external oblique muscle for which there are various methods of surgical repair. See also abdominal muscles.
hexokinase see muscle enzymes.
Hick’s law a law specifying the linear relationship between choice reaction time and the number of response options available, stating that choice reaction time increases as a function of the logarithm of the number of alternatives. See also reaction time.
high-carbohydrate diet see carbohydrate (CHO), carbohydrate intake guidelines for athletes, carbohydrate loading.
high energy bond chemical bond which is readily hydrolysed by an appropriate catalyst, and releases a large amount of energy when the hydrolysis occurs in the cytoplasm of a living cell; this energy release depends as much on the products of the hydrolysis being present at very low concentrations as it does on the properties of the bond itself. Key instances in muscle are the terminal phosphate bonds of adenosine triphosphate and phosphocreatine.
high-fat diet one which provides more than 30% of energy as fat. Research into effects on performance indicates that 3–5 days on a high-fat diet leads to deterioration of endurance performance when compared to a carbohydrate (CHO)-rich diet. However, when adaptation to the diets is combined with training for a period of 1–4 weeks, a high-fat diet does not attenuate endurance performance compared to a high-CHO diet. When such regimes are continued and compared for longer than 4 weeks, endurance performance is markedly better on the CHO-rich diet. There is no performance benefit in switching to high-CHO after long-term adaptation to high-fat, compared to having a high-CHO diet all along.
high-protein diet one which provides more than 15% of energy as protein. Traditionally, high-protein diets are low-carbohydrate diets. These diets are claimed to be effective for the reduction of body mass and body fat. Extremely high-protein diets are claimed to suppress appetite through reliance on fat mobilization and ketone body formation. In addition, the elevated thermic effect of dietary protein, with a relatively low coefficient of digestibility (particularly in the case of plant proteins), reduces the net calories available from ingested protein compared with a well-balanced diet of equivalent caloric value. The long-term success of high-protein diets remains questionable and they may even pose health risks, including kidney damage, increased blood lipoprotein levels and dehydration. See also low-carbohydrate ketogenic diets.
hip joint a ‘ball-and-socket’ joint, where the globular head of the femur articulates with the cup-like hollow (the acetabulum) in the hip bone, which is deepened by a fibrocartilaginous rim; the joint is strongly supported by ligaments attached to this rim and the hip bone above, and to the femur where the neck joins the shaft. hip injury is important in sport as the initial treatment usually requires non-weight-bearing activity only and then often a prolonged rehabilitation. acute injuries can be the result of a fall, direct trauma or twisting; they include fractures, dislocations and soft tissue injuries to muscles and supporting ligaments. overuse injuries result from repetitive weight-bearing activity, such as road running, and include bursitis and tendonitis. See also appendix 1.2 figs 1, 2.
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