P
pacemaker the region of the heart, normally the sinoatrial node, that rhythmically initiates the cardiac action potential and hence the whole electrical and mechanical cardiac cycle, varying the heart rate under the influence of the sympathetic and parasympathetic nerve supply. An artificial pacemaker may be implanted when normal rhythm generation is affected by heart disease.
packed cell volume see haematocrit.
pain the name that we give to the unpleasant and disturbing subjective experience that results from injury or other damage. Sensory receptors involved are known as nociceptors (from the adj noxious meaning harmful); thence afferent nerve impulses reach the central nervous system (CNS), where different influences can diminish or enhance them, acting where they are relayed and transmitted to the cerebral cortex and conscious perception. The pain pathways are separate from those serving other sensations, and even vigorous stimulation of other sensory receptors does not, by itself, cause pain. pain management involves a multdisciplinary approach, often by a specialist team. See also endorphins, transcutaneous electromagnetic nerve stimulation (TENS).
palpation examination of a body area by touch.
palpitation beating of the heart of which a person is strongly aware, as being rapid and/or forceful, or sometimes irregular. May be both unpleasant and worrying but most will experience palpitation on occasion. Physiological causes include exercise, excitement, caffeine intake, smoking and alcohol. May also be a symptom of underlying disease, e.g. anaemia, hyperthyroidism, cardiac disease (especially if linked with other symptoms such as faintness, sweating, chest pain). Investigations (ECG, ambulatory monitoring, echocardiography, exercise test) are used to identify the nature of the condition and possible underlying causes.
panting rapid shallow breathing; a mechanism in furry animals for losing heat. In humans, not a normal physiological pattern of breathing. See also hyperventilation, tachypnoea.
paradigm term introduced ca 1960 by the science-historian Kuhn; a widely followed way of approaching an area of research, deriving from a notable early achievement in the field and carrying forward both its experimental methodology and its theoretical outlook.
paraesthesia the sensations commonly known as pins and needles; may be due to pressure on, or damage to, a nerve or may have no evident cause.
parallel axis theorem mathematical method of relating the moment of inertia of a body or object around one axis to the moment of inertia of the same body or object around a parallel axis. Calculated as I2 = I1 + md2 where I1 and I2 are the moments of inertia, m is the mass of the object and d is the distance between the two parallel axes.
paralympics the competitive events regularly held ‘parallel to the Olympics’ for disabled sportspeople. In the late 1940s Ludwig Guttmann, medical director of the Stoke Mandeville Spinal Injuries Unit, who had made wheelchair games a feature of rehabilitation, initiated competitive events in archery, netball and table tennis for his paraplegic patients. In 1952 he invited a small Dutch team to join in the local games, and this first international event led to his inauguration of the paralympics in Rome in 1960, with 400 wheelchair athletes. By 2004 successive occasions had extended the range of disabilities included, and there were 19 events for 4000 participants from 136 countries. See also spinal injury.
paralysis loss of muscle function, due to damage at any level in the pathway for neural activation, or to muscle disease or relaxant drugs. See also spinal injury.
paraparesis incomplete loss of motor function in the lower half of the body.
paraplegia paralysis of the lower part of the body, including both lower limbs. paraplegic adj. See also spinal injury.
parasympathetic nervous system one of the two components of the autonomic nervous system. Preganglionic nerve fibres come from the brain stem and from the sacral segments of the spinal cord (‘craniosacral outflow’), i.e. from the central nervous system above and below the sympathetic outflow. These nerves relay in ganglia close to the organs where they act (including heart, lungs, gastrointestinal tract). Most of the cranial components travel in the vagus nerves. In general, parasympathetic nerves stimulate the functions of the alimentary and genitourinary systems, whereas effects on the cardiorespiratory system are appropriate to relative inactivity, e.g. slowing the heart rate. See also acetylcholine, atropine, sympathetic nervous system; appendix 1.1 figs 5, 6.
parathyroid glands small clumps of endocrine tissue (usually four) on the back of the thyroid gland which secrete parathyroid homone (PTH). This acts to increase calcium ion concentration in the extracellular fluid, counterbalanced by calcitonin from the thyroid gland which has the opposite effects. Together they correct any changes in blood [Ca2+] by action on absorption of calcium from the gut, its deposition in bone and its excretion by the kidneys. See also hormones; appendix 5.
partial pressure the component of the total gas pressure accounted for by one gas in a mixture of gases, e.g. in air at 1 standard atmosphere (1 bar, ∼101 kPa, 760 mmHg or torr), 21% is oxygen and the partial pressure of oxygen (PO2) is ∼21 kPa or 160 mmHg (torr). Partial pressure (syn tension) of a gas dissolved in a liquid is defined as the partial pressure of that gas in the gaseous phase with which the liquid is, has been or would be, in equilibrium. So, given near-perfect diffusion equilibrium across the alveolar-capillary membranes, blood leaves the lungs with virtually the same PO2 and PCO2 as in alveolar gas (normally close to 100 mmHg PO2 and 40 mmHg PCO2). When blood reaches capillaries in active tissues, the lower PO2 and higher PCO2 in tissue fluids cause net molecular movement towards equilibrium, so that O2 is removed from the blood and CO2 taken up. See also carbon dioxide, diffusing capacity, gas exchange, nitrogen, oxygen, oxyhaemoglobin dissociation curve.
participation motive an individual’s reason for engaging in activity. Often applied to reasons for engaging in exercise or sport, such as to manage weight, for enjoyment or for social reasons.
patella the knee cap. patellar tendon syn patellar ligament the strong flat fibrous band that runs from the lower margin of the patella to the tibial tubercle (tuberosity). The more superficial fibres are in fact continuous over the front of the patella with the quadriceps tendon, effectively providing insertion of the quadriceps onto the tibia. Injury is seen in jumping sports. patellar tendonitis inflammation of the patellar tendon. Causes include a change in training (intensity, frequency or type, e.g. more repetitive running on a hard surface), poor muscle strength and altered biomechanics at the knee. This results in pain and swelling over the tendon, especially after activity. Common in jumping sports such as basketball and athletics (jumper’s knee). Treatment is as for any soft tissue injury. Rehabilitation includes changing technique, altering training load, biomechanical assessment and muscle strengthening. See also knee joint; appendix 1.2 figs 1, 2.
Pavlovian conditioning see conditioning.
peak expiratory flow rate (PEFR) the highest flow rate at the mouth during a rapid forced expiration, starting with the lungs at full capacity. Peak occurs almost immediately after the start of exhalation. Reduced in obstructive lung disease (asthma, bronchitis, emphysema). See also lung volumes.
peak force the greatest recorded instantaneous force on an object or body (e.g. during gait analysis).
peak performance a state in which the person performs to the maximum of their ability, characterized by subjective feelings of confidence, effortlessness and total concentration on the task.
pectoral muscles group of muscles on the front of the chest which link the trunk to the upper limb. pectoralis major the largest and most superficial, takes origin from the clavicle, sternum and ribs and crosses the front of the shoulder to insertions into the clavicle and humerus. See appendix 1.2 fig 5A.
pedometer device for counting the number of strides taken in a given period or event. Almost all modern pedometers also provide estimates of distance covered and average speed, based upon a user-entered mean value of stride length.
peer group a social group composed of people of a similar age or status.
peer support the social support provided by one’s peer group.
pelvis (from Latin meaning ‘basin’) the bony framework of the lowest part of the trunk, where the hip bones together with the sacrum and coccyx enclose the pelvic cavity, which is continuous above with the abdominal cavity. Each hip bone has three fused components: the ilium with a flared upper rim, the iliac crest, and linked to the sacrum at the sacroiliac joint; the ischium with the socket for the head of the femur (the acetabulum) at the hip joint; and the pubis which is attached to its partner at the pubic symphysis, centre front. See appendix 1.2 figs 1, 2.
perception the act or process of becoming aware of internal or external sensory stimuli or events, involving the meaningful organization and interpretation of those stimuli. In psychology, perception also applies to evaluations of one’s own and others’ internal states and beliefs as well as sensory stimuli and a person’s perceptions are not necessarily identical to the stimulus object or event being perceived. For example, a person’s perceptions of their ability might not match their actual ability. Perception is to be distinguished from sensation which refers to the subjective experience that results from excitation of the sensory apparatus without any interpretation or imposition of meaning.
perceptual motor skill any skill involving the interaction and integration of perceptual processes and voluntary physical movement, such as the ability to perform a gymnastic routine.
performance the act of producing a co-ordinated sequence of behaviours. See also ability, skill.
performance genes the potential uses of genetic profiling and gene therapy within sport remain experimental and controversial. Suggested applications include (1) identification of potential athletes by the presence of the so-called performance genes, which may enable an athlete to perform at a higher level by their influence on muscle metabolism and endurance; (2) use as a ‘screening’ tool to identify athletes with particular body shape, e.g. tall athletes for basketball. This could result in discrimination and have implications for the funding for young athletes, should funding be withheld from those who ‘fail’ to have the ideal body habitus; (3) identification of those athletes who have a genetic predisposition to sports-related injury. Other moral dilemmas exist in this area. Should the limited funding for genetic research be used to enhance sports performance at the expense of research into disease prevention Should we limit opportunities within sport and exercise because the young person does not have the ideal ‘genetic makeup’ The World Anti-Doping Agency (WADA) and the International Olympic Committee have recently included the non-therapeutic use of genes, genetic elements and/or cells that have the capacity to enhance athletic performance in their list of proscribed substances and methods. They will continue to monitor the use of genetic testing and genetic information for identifying or selecting athletes, with a view to developing policies and guidelines for sports organizations and athletes. See also human enhancement technologies (HET).
performance goal (1) a goal focused on gaining favourable judgements or avoiding unfavourable judgements by others; (2) a goal that specifies the achievement of an endproduct of performance that is relatively independent of the performance of other people, such as running a race in a certain time rather than beating others. See also ego involvement, learning goal, process goal, outcome goal.
performance profiling a method for helping athletes to identify their strengths and weaknesses in order to encourage them to be fully involved in decisions about developing appropriate training programmes to enhance their performance. It typically involves asking athletes to identify what they think are the major characteristics of an elite performer in their sport and then to rate themselves on those characteristics.
perfusion in physiology and pathology, refers to blood flow in a region, organ or tissue; hypoperfusion inadequate blood flow.
peripheral nervous system (PNS) all nerve cells and fibres that are outside the central nervous system (CNS, the brain and spinal cord) and which connect all parts of the body with the CNS. Includes the somatic nervous system – the nerves to skeletal muscles and from neural receptors in the musculoskeletal system and the skin, and the autonomic nervous system which controls the functions of the organs, the glands and the cardiovascular system via the outgoing nerves of its two divisions, the sympathetic nervous system and the parasympathetic nervous system; together with their associated visceral afferents. See appendix 1.1 figs 3–5.
peripheral resistance the sum total of resistance to blood flow in the systemic circulation, mostly located in the arterioles, dependent on the constriction/relaxation of the smooth muscle in their walls. The balance between cardiac output and total peripheral resistance determines the arterial blood pressure (BP), and physiological adjustments of either or both are the means of maintaining BP despite variations in local vasodilatation/vasoconstriction in different organs and tissues.
personal construct theory a theory of personality first described by American psychologist George Kelly in 1955 that views the person as actively constructing their view of reality and acting as an incipient scientist, constantly formulating and testing hypotheses about their world in order to bring sense and meaning to their lives.
personality the totality of behavioural, psychological and emotional characteristics that make a person an individual. See also big five, trait.
Perthes’ disease avascular degeneration of the upper femoral epiphysis. Occurs in children aged 4–8, five times more commonly in boys, causing a limp, which may be painless. Revascularization occurs but residual deformity of the femoral head may subsequently lead to arthritic changes. Diagnosed on clinical suspicion with X-ray confirmation. Treatment aims to minimize the deformity and includes rest, traction, plaster cast or occasionally surgery (described in 1910 by German orthopaedic surgeon G. C. Perthes).
pes cavus high-arched or claw foot. An acquired or congenital condition, which results from plantarflexion of the forefoot relative to the rearfoot, with elevation of the longitudinal arch. Associated with clawing of the toes, depression of the first metatarsal and hindfoot varus. May be the result of underlying neuromuscular disease. Can present with pain, difficulty in getting suitable shoes or obvious foot deformity. In sport, good podiatry input and correctly fitted shoes will minimize secondary effects, which are seen primarily in weight-bearing sports.
pes planus aka flat foot an abnormally low longitudinal arch causes a greater contact area with the ground. Most do not cause problems but can result in loss of the gripping action of the toes, causing pain and discomfort during weight-bearing, especially when running. The foot becomes more rigid with age, with increased risk of later osteoarthritis. Common in children when the longitudinal arch has not yet developed.
pH the negative logarithm of the hydrogen ion concentration [H+], so a change by one pH unit means a tenfold change in [H+]. pH 7 represents neutrality in water at 25°C, when [H+] = 10−7 molar = 100 nmol.L−1. In the body, at 37°C, ‘neutral’ would be ∼pH 6.8 but the extracellular pH of body fluids is more alkaline than this. Arterial blood pH (the most readily measured) varies in health within the range of 7.36–7.44 or [H+] = 40 nmol.L−1 ±about 12% – a tiny amount compared to other ions in the blood. intracellular pH is more acidic (e.g. 6.8–7.1 in skeletal muscle fibres), so there is a gradient promoting exit of metabolically generated H+ from cells. Regulation, vital for normal metabolic processes, depends on this gradient, on intracellular buffers (predominantly proteins and phosphates) and on variations in PCO2. The whole-body turnover of H+ (by ingestion, metabolic production and excretion) is of vastly greater magnitude than the body fluid concentrations. See also acid–base balance.
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