L
labyrinthitis inflammation of the inner ear resulting in disturbance of balance and co-ordination. Dizziness, nausea and loss of balance, especially on head movement, are the commonest symptoms and these will impair performance in sport until they settle. Most commonly caused by a viral infection. Recovery may take some weeks and exercise should be avoided until symptoms have resolved completely. See also ear, vestibular apparatus.
Lachman test an alternative to the anterior drawer test in assessment of the integrity of the anterior cruciate ligament (ACL), useful as it removes the limitation of the anterior drawer when the hamstrings contract, but is sometimes difficult to perform in athletes with well-developed musculature or where the examiner has small hands. With the patient on a couch, the examiner holds the thigh firmly and flexes the knee to around 20°. The tibia is then drawn forwards to assess cruciate integrity compared to the uninjured knee. The test is graded on the magnitude of movement and whether there is a firm or soft endpoint.
lactacid oxygen debt component of oxygen debt required to eliminate lactic acid after intense exercise; constitutes the slow phase of return to resting condition.
lactate the anion of lactic acid and its salts, although the term ‘lactate’ is commonly, but incorrectly, used interchangeably with ‘lactic acid’ itself. At rest and during prolonged moderate exercise, lactate level in the blood is low (0.7–1.4 mmol.L−1). In short-term, high-intensity exercise, lactate production in muscles, and its efflux from them, exceeds its rate of removal from the circulating blood, causing a steep increase in the concentrations of lactate and of hydrogen ions [H+] both in muscle itself and in the blood. Lactate measured in blood therefore reflects the balance between release from exercising muscles and uptake (by the liver, cardiac muscle and any skeletal muscle fibres which are not themselves under anaerobic stress). Contrary to earlier assumptions, lactate is not itself deleterious to most physiological processes and can be used as fuel by well-oxygenated cells, including muscle fibres, but accumulation of H+ in muscle fibres can slow glycolysis and interfere with force generation, while in the extracellular fluid it is thought to contribute, at extremes, to the stimulation of pain receptors. The raised [H+] in the blood acts as an additional stimulus to ventilation, but it impairs fat oxidation by reducing release of free fatty acids from adipose tissue. See also anaerobic exercise, metabolic and related thresholds, monocarboxylate transporters.
lactate analyser instrument for estimating the concentration of lactate in a sample of fluid, most often blood or plasma.
lactate dehydrogenase (LDH) see muscle enzymes.
lactate threshold see metabolic and related thresholds.
lactic acid three-carbon molecule formed by reduction of pyruvic acid in last step of anaerobic glycolysis; dissociates to form lactate and hydrogen ions (H+). See also monocarboxylate transporters.
lactic acid system old term for anaerobic glycolysis, referring to the production of energy by this metabolic pathway in intensive exercise of duration less than about 2 min, or in the first 40 s or so of less intensive exercise before aerobic metabolism has been fully activated. See also anaerobic exercise.
lactose a disaccharide of glucose and galactose; the major sugar in human and bovine milk (milk sugar). The least sweet of disaccharides, lactose can be artificially processed and is often present in carbohydrate-rich, high-calorie drinks. Broken down to glucose and galactose in the small intestine by the action of the enzyme lactase. In some individuals who have lactase deficiency, ingestion leads to accumulation of gas and fluid in the large intestine, with pain and diarrhoea.
lateral (to) at or towards the side. In anatomy, describes position of a structure as further from the middle of the body, in the coronal (side-to-side) plane, when in the anatomical position. Opposite of medial.
lateral compartment syndrome see compartment syndrome.
laws of motion see Newton’s laws of motion.
laxatives agents that promote evacuation of the bowel, cathartic or purgative. In sports with weight categories, laxatives (sometimes in combination with food and fluid restriction, excessive exercise and use of sauna and diuretics) are used to lose weight quickly prior to weigh-in; this may diminish physical performance or lead to abnormalities of bone metabolism, impairments in cognitive function and increased susceptibility to heat illness. See also bulimia.
leadership style the manner in which a leader typically provides direction and motivates others. autocratic leadership style when the leader takes a dominant, directive role; democratic leadership style when the leader consults with the team and involves them in the process of making decisions.
lean body mass (LBM) see body composition.
learned helplessness a state of apathy and hopelessness in which the individual feels unable to affect outcomes, resulting from repeated exposure to uncontrollable situations.
learning is used to mean (1) a relatively permanent change in behaviour as a result of experience, (2) the state of having knowledge or skills, (3) being in the process of acquiring knowledge or skills. explicit learning or knowledge is acquired through conscious, deliberate intention to master or understand a task; implicit learning or knowledge is acquired passively, without conscious awareness or deliberate effort; incidental learning or knowledge of a task is acquired unintentionally during the acquisition of another task.
learning goal a goal focused on personal improvement in performance. See also task involvement, performance goal.
leg length discrepancy difference in the true length of one leg compared to the other. It may be structural (secondary to a pre-existing condition such as Perthes’ disease) or functional as a result of altered lower limb biomechanics. Differences of 0.5–1 cm are not uncommon and usually asymptomatic. Greater discrepancy will produce a compensatory pelvic tilt or secondary scoliosis (lateral curvature of the spine). This compensation, combined with repetitive exercise, can cause problems including discomfort in the back, lower limb (especially knee) pain or Achilles tendonitis. Treatment includes improving pelvic control and core stability and the use of orthoses. It is important to identify this problem to allow correct treatment, as treatment of the secondary effect alone will not alleviate the symptoms.
length–tension relationship the relation between a muscle’s length and the isometric tension (force) which it generates when fully activated. During normal muscular activity, particularly at the longer lengths, tension partly depends on passive stretch of the connective tissue within the muscle, acting in parallel with active force generation by the muscle fibres themselves. When this contribution is subtracted, and only the actively generated force considered, the relation between force and length depends predominantly on the number of actin-myosin cross-bridges (XB) which can be formed. Diagram A shows the relationship for skeletal muscle in terms of sarcomere length. Diagram B illustrates how this is accounted for by variations in overlap between thick and thin filaments, and therefore in the formation of cross-bridges. Over the range of decreasing sarcomere length (I–II) progressively more XB can form but when the shortest length (IV) is approached, correctly oriented XB formation diminishes as the thin filaments begin to overlap and force declines. Most muscles in the body operate only over the central, high force, part of the curve shown in A. See also muscle contraction, myofibrils, sliding filament mechanism.
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