Showing papers in "Sports Medicine in 1991"

A Meta-Analysis on the Anxiety-Reducing Effects of Acute and Chronic Exercise: Outcomes and Mechanisms

Abstract: The relationship between exercise and anxiety has been extensively examined over the last 15 years. Three separate meta-analyses were conducted to quantitatively review the exercise-anxiety literature for state anxiety, trait anxiety and psychophysiological correlates of anxiety. Such a procedure allows tendencies of the research to be characterised.

Mechanisms of exercise-induced muscle fibre injury

Abstract: Exercise for which a skeletal muscle is not adequately conditioned results in focal sites of injury distributed within and among the fibres. Exercise with eccentric contractions is particularly damaging. The injury process can be hypothesised to occur in several stages. First, an initial phase serves to inaugurate the sequence. Hypotheses for the initial event can be categorised as either physical or metabolic in nature. We argue that the initial event is physical, that stresses imposed on sarcolemma by sarcomere length inhomogeneities occurring during eccentric contractions cause disruption of the normal permeability barrier provided by the cell membrane and basal lamina. This structural disturbance allows Ca++ to enter the fibre down its electrochemical gradient, precipitating the Ca++ overload phase. If the breaks in the sarcolemma are relatively minor, the entering Ca++ may be adequately handled by ATPase pumps that sequester and extrude Ca++ from the cytoplasm ('reversible' injury). However, if the Ca++ influx overwhelms the Ca++ pumps and free cytosolic Ca++ concentration rises, the injury becomes 'irreversible'. Elevations in intracellular Ca++ levels activate a number of Ca(++)-dependent proteolytic and phospholipolytic pathways that are indigenous to the muscle fibres, which respectively degrade structural and contractile proteins and membrane phospholipids; for instance, it has been demonstrated that elevation of intracellular Ca++ levels with Ca++ ionophores results in loss of creatine kinase activity from the fibres through activation of phospholipase A2 and subsequent production of leukotrienes. This autogenetic phase occurs prior to arrival of phagocytic cells, and continues during the inflammatory period when macrophages and other phagocytic cells are active at the damage site. The phagocytic phase is in evidence by 2 to 6 hours after the injury, and proceeds for several days. The regenerative phase then restores the muscle fibre to its normal condition. Repair of the muscle fibres appears to be complete; the fibres adapt during this process so that future bouts of exercise of similar type, intensity, and duration cause less injury to the muscle.

Overtraining in athletes. An update.

Abstract: Overtraining appears to be caused by too much high intensity training and/or too little regeneration (recovery) time often combined with other training and nontraining stressors. There are a multitude of symptoms of overtraining, the expression of which vary depending upon the athlete's physical and physiological makeup, type of exercise undertaken and other factors. The aetiology of overtraining may therefore be different in different people suggesting the need to be aware of a wide variety of parameters as markers of overtraining. At present there is no one single diagnostic test that can define overtraining. The recognition of overtraining requires the identification of stress indicators which do not return to baseline following a period of regeneration. Possible indicators include an imbalance of the neuroendocrine system, suppression of the immune system, indicators of muscle damage, depressed muscle glycogen reserves, deteriorating aerobic, ventilatory and cardiac efficiency, a depressed psychological profile, and poor performance in sport specific tests, e.g. time trials. Screening for changes in parameters indicative of overtraining needs to be a routine component of the training programme and must be incorporated into the programme in such a way that the short term fatigue associated with overload training is not confused with the chronic fatigue characteristic of overtraining. An in-depth knowledge of periodisation of training theory may be necessary to promote optimal performance improvements, prevent overtraining, and develop a system for incorporating a screening system into the training programme. Screening for overtraining and performance improvements must occur at the culmination of regeneration periods.

The induction and decay of heat acclimatisation in trained athletes

Abstract: Heat acclimatisation/acclimation involves a complex of adaptations which includes decreased heart rate, rectal temperature, perceived exertion as well as increased plasma volume and sweat rate. These adaptations serve to reduce physiological strain, improve an athlete’s ability to exercise in a hot environment, and reduce the incidence of some forms of heat illness. Few differences exist in the ability of men and women to acclimatise to heat. Typically, older runners do not perform in the heat as well as younger runners, but physical training can negate differences between these groups. Hormonal adaptations (e.g. aldosterone, vasopressin) during heat acclimatisation encourage fluid-electrolyte retention and cardiovascular stability. Athletes with high maximal aerobic power (VO2max) acclimatise to heat faster (and lose adaptations slower when they are inactive in a cool environment) than athletes with low VO2max values. Physical training in a cool environment improves physiological responses to exercise at high ambient temperatures. In attempting to optimise heat acclimatisation, athletes should maintain fluid-electrolyte balance, exercise at intensities greater than 50% VO2max for 10 to 14 days, and avoid factors (e.g. sleep loss, infectious disease) which are known to reduce heat tolerance. Once acclimatisation has been achieved, inactivity results in a decay of favourable adaptations, after only a few days or weeks.

Kinetic chain exercise in knee rehabilitation.

Abstract: Rehabilitation is recognised as a critical component in the treatment of the anterior cruciate ligament (ACL) injured athlete, and has been the subject of intense research over the past decade. As a result, sound scientific principles have been applied to this realm of sports medicine, and have improved the outcome of both surgical and nonsurgical treatment. Possibly the most intriguing of these principles is the use of the kinetic chain concept in exercise prescription following ACL reconstruction. The hip, knee, and ankle joints when taken together, comprise the lower extremity kinetic chain. Kinetic chain exercises like the squat recruit all 3 links in unison while exercises such as seated quadriceps extensions isolate one link of the chain. Biomechanical assessment with force diagrams reveals that ACL strain is reduced during kinetic chain exercise by virtue of the axial orientation of the applied load and muscular co-contraction. Additionally, kinetic chain exercise through recruitment of all hip, knee, and ankle extensors in synchrony takes advantage of specificity of training principles. More importantly, however, it is the only way to reproduce the concurrent shift of 'antagonistic' biarticular muscle groups that occurs during simultaneous hip, knee, and ankle extension. Incoordination of the concurrent shift fostered by exercising each muscle group in isolation may ultimately hamper complete recovery. Modifying present day leg press and isokinetic equipment will allow clinicians to make better use of kinetic chain exercise and allow safe isokinetic testing of the ACL reconstructed knee. Reconstruction of the ACL with a strong well placed graft to restore joint kinematics, followed by scientifically sound rehabilitation to improve dynamic control of tibial translation, will improve the outcome after ACL injury.

Biomechanical factors associated with injury during landing in jump sports.

Abstract: Many sport and movement activities contain a jumping component which necessitates landing. Several injury surveys across a variety of jump sports have identified the lower extremities and specifically the knee joint as being a primary injury site. Factors which might contribute to the frequency and severity of such injuries include stresses to which the body is subjected during performance (forces and torques), body position at landing, performance execution and landing surface. Most of the initial landing studies were primarily descriptive in nature with many of the more recent efforts being directed toward identifying the specific performance factors that could account for the observed system stresses. Continued investigations into landing are necessary to more thoroughly understand the force attenuation mechanisms and critical performance variables associated with lower extremity injuries.

Muscle glycogen synthesis before and after exercise.

Abstract: The importance of carbohydrates as a fuel source during endurance exercise has been known for 60 years. With the advent of the muscle biopsy needle in the 1960s, it was determined that the major source of carbohydrate during exercise was the muscle glycogen stores. It was demonstrated that the capacity to exercise at intensities between 65 to 75% VO2max was related to the pre-exercise level of muscle glycogen, i.e. the greater the muscle glycogen stores, the longer the exercise time to exhaustion. Because of the paramount importance of muscle glycogen during prolonged, intense exercise, a considerable amount of research has been conducted in an attempt to design the best regimen to elevate the muscle's glycogen stores prior to competition and to determine the most effective means of rapidly replenishing the muscle glycogen stores after exercise. The rate-limiting step in glycogen synthesis is the transfer of glucose from uridine diphosphate-glucose to an amylose chain. This reaction is catalysed by the enzyme glycogen synthase which can exist in a glucose-6-phosphate-dependent, inactive form (D-form) and a glucose-6-phosphate-independent, active form (I-form). The conversion of glycogen synthase from one form to the other is controlled by phosphorylation-dephosphorylation reactions. The muscle glycogen concentration can vary greatly depending on training status, exercise routines and diet. The pattern of muscle glycogen resynthesis following exercise-induced depletion is biphasic. Following the cessation of exercise and with adequate carbohydrate consumption, muscle glycogen is rapidly resynthesised to near pre-exercise levels within 24 hours. Muscle glycogen then increases very gradually to above-normal levels over the next few days. Contributing to the rapid phase of glycogen resynthesis is an increase in the percentage of glycogen synthase I, an increase in the muscle cell membrane permeability to glucose, and an increase in the muscle's sensitivity to insulin. The slow phase of glycogen synthesis appears to be under the control of an intermediate form of glycogen synthase that is highly sensitive to glucose-6-phosphate activation. Conversion of the enzyme to this intermediate form may be due to the muscle tissue being constantly exposed to an elevated plasma insulin concentration subsequent to several days of high carbohydrate consumption. For optimal training performance, muscle glycogen stores must be replenished on a daily basis. For the average endurance athlete, a daily carbohydrate consumption of 500 to 600g is required. This results in a maximum glycogen storage of 80 to 100 mumol/g wet weight.(ABSTRACT TRUNCATED AT 400 WORDS)

Osteitis pubis in athletes. Infection, inflammation or injury?

Abstract: Medical records of 59 patients (9 females and 50 males), who presented to sports medicine clinics at the Australian Institute of Sport and the University of British Columbia between 1985 and 1990 and who were diagnosed as suffering osteitis pubis, were reviewed and comparison of data obtained was made with the literature. Women average 35.5 years of age (30 to 59 years) and men 30.3 years (13 to 61 years). Sports most frequently involved were running, soccer, ice hockey and tennis. Clinical presentations of osteitis pubis fell into 4 main groups. ‘Mechanical’ (sport-related) was the largest group (n = 48), followed by ‘obstetric’ (n = 5), ‘inflammatory’ (n = 4) and ‘other’ (n = 2). Period of follow-up averaged 10.3 months (1 to 20 months) in women and 17.5 months (2 to 96 months) in men. Full recovery, when documented, averaged 9.5 months in men and 7.0 months in women. Osteitis pubis recurred in 25% of these men and none of these women at follow-up. The most frequent symptoms were pubic pain and adductor pain. Men also presented with lower abdominal, hip and perineal or scrotal pain; women with hip pain. Most common signs were tenderness of the pubic symphysis and tenderness of adductor longus muscle origin. Men also revealed tenderness of one or both the superior pubic rami and evidence of decreased hip rotation (unilateral or bilateral). Evidence of pelvic malalignment and/or sacroiliac dysfunction was frequently seen in both men and women. There was poor correlation between radiographic and isotope bone scan findings and the site and duration of symptoms and signs. Femoral head ratios were estimated on 30 hips in the series and 2 were judged to be at the upper limit of normal, perhaps indicating a form of epiphysiolysis producing tilt deformity of the head of the femur.

Low back pain in young athletes. A practical approach.

Abstract: Lumbar spine pain accounts for 5 to 8% of athletic injuries. Although back pain is not the most common injury, it is one of the most challenging for the sports physician to diagnose and treat. Factors predisposing the young athlete to back injury include the growth spurt, abrupt increases in training intensity or frequency, improper technique, unsuitable sports equipment, and leg-length inequality. Poor strength of the back extensor and abdominal musculature, and inflexibility of the lumbar spine, hamstrings and hip flexor muscles may contribute to chronic low back pain. Excessive lifting and twisting may produce sprains and strains, the most common cause of low back pain in adolescents. Blows to the spine may create contusions or fractures. Fractures in adolescents from severe trauma include compression fracture, comminuted fracture, fracture of the growth plate at the vertebral end plate, lumbar transverse process fracture, and a fracture of the spinous process. Athletes who participate in sports involving repeated and forceful hyperextension of the spine may suffer from lumbar facet syndrome, spondylolysis, or spondylolisthesis. The large sacroiliac joint is also prone to irritation. The signs and symptoms of disc herniation in adolescents may be more subtle than in adults. Disorders simulating athletic injury include tumours and inflammatory connective tissue disease. Often, however, a specific diagnosis cannot be made in the young athlete with a low back injury due to the lack of pain localisation and the anatomic complexity of the lumbar spine. A thorough history and physical examination are usually more productive in determining a diagnosis and guiding treatment than imaging techniques. Diagnostic tests may be considered, though, for the adolescent athlete whose back pain is severe, was caused by acute trauma, or fails to improve with conservative therapy after several weeks. Radiographs, bone scanning, computed tomography, and magnetic resonance imaging may help identify, or exclude serious pathology. Fortunately, the majority of cases of low back pain in adolescents respond to conservative therapy. Immediate treatment of an acute injury, such as a sprain or strain, includes cryotherapy, electrogalvanic stimulation, anti-inflammatory medications and gentle exercises. Prolonged bed rest should be avoided since atrophy may occur rapidly. Strong analgesics are also usually contraindicated, except for sleep, since they mask pain and may allow overvigorous activity. Early strengthening exercises include the Williams flexion exercises and/or McKenzie extension exercises. Both exercise motions may often be prescribed. Athletes with an acute disc herniation, however, should only perform extension exercises initially. Athletes with spondylolysis, spondylolisthesis and facet joint irritation should initially be limited to flexion exercises.(ABSTRACT TRUNCATED AT 400 WORDS)

Common cycling injuries. management and prevention

Abstract: The increasing participation in the athletic forms of bicycling warrants expanded physician attention to the traumatic and overuse injuries experienced by cyclists. The modern bicycle consists of a frame with various components, including handlebars, brakes, wheels, pedals, and gears, in various configurations for the various modes of cycling. For high performance cycling the proper fit of the bicycle is critical. The most efficient method to provide an accurate fit is the Fitkit, but proper frame selection and adjustment can be made by following simple guidelines for frame size, seat height, fore and aft saddle position, saddle angle, reach and handlebar height. The human body functions most effectively in a narrow range of pedal resistance to effort. Riding at too much pedal resistance is a major cause of overuse problems in cyclists. Overuse injuries are lower using lower gear ratios at a higher cadence. Cycling injuries account for 500,000 visits per year to emergency rooms in the US. Over half the accidents involve motor vehicles, and road surface and mechanical problems with the bicycle are also common causes of accidents. Head injuries are common in cyclists and account for most of the fatal accidents. Despite good evidence of their effectiveness, victims with head injuries have rarely worn helmets. Contusions, sprains and fractures may occur throughout the body, most commonly to the hand, wrist, lower arm, shoulder, ankle and lower leg. The handlebar and seat have been implicated in a wide variety of abdominal and genital injuries. Abrasions, lacerations and bruises of the skin are the most common traumatic injuries. Trauma may be prevented or reduced by proper protective safety equipment and keeping the bike in top mechanical condition. Anticipation of the errors of others and practising and adopting specific riding strategies also help to prevent traumatic injuries. Management of overuse injuries in cycling generally involves mechanical adjustment as well as medical management. Neck and back pain are extremely common in cyclists, occurring in up to 60% of riders. Ulnar neuropathy, characterised by tingling, numbness and weakness in the hands is common in serious cyclists after several days of riding. Managing saddle-related injuries or irritations may also involve adjusting seat height, angle and fore and aft position in addition to changing the saddle. Padding in the saddle and shorts play an important part in saddle problems. Saddle-related problems include chafing, perineal folliculitis and furuncles, subcutaneous perineal nodules, pudendal neuropathy, male impotence, traumatic urethritis and a variety of vulva trauma.(ABSTRACT TRUNCATED AT 400 WORDS)

Health- and performance-related potential of resistance training.

Abstract: Regular physical activity can improve cardiovascular fitness and may reduce the likelihood and debilitating effects of cardiovascular disease. Weight-training has generally been believed to have limited value in modifying risks of cardiovascular disease. Effects shown of resistance training on parameters associated with cardiovascular fitness and disease include: heart rate decreases for maximal work and recovery from short term weight-training, increased ventricular mass, and increased ventricular wall and septum thickness. Studies suggest that myocardial hypertrophy resulting from resistive training can be accompanied by positive myocardial adaptations. Blood pressure response considerations to resistive training include: similarity of resistive exercise peak response to other forms of high intensity exercise, highest blood pressures occur at or near exhaustion during maximum lifts, training appears to reduce the exercise blood pressure. Given the blood pressure responses caution is required for individuals with cardiovascular disease. Studies of high-volume weight-training indicate that small to moderate increases in aerobic power can occur in relatively short periods of time. The mechanisms by which weight-training increases VO2max is unclear. Resistive training may produce positive changes in serum lipids with the volume of training being the dependent factor. Cross-sectional and longitudinal studies of bodybuilders suggest that weight-training may beneficially alter glucose tolerance and insulin sensitivity. It appears that weight-training can increase short term high intensity endurance without a concomitant loss in performance. Resistive training increases power output and performance. Body composition has important relationships to cardiovascular fitness, strength and flexibility. It is likely that it can be affected and controlled by use of large body mass during exercise depending on training volume.

Quantification of training in competitive sports. Methods and applications.

Abstract: The training of competitive athletes can be assessed by retrospective questionnaires, diaries, physiological monitoring and direct observation of training behaviour. Questionnaires represent the most economical, most comprehensive and least accurate method. Diaries are more valid, but their drawbacks for long term quantitative studies are poor compliance and difficulties in processing the data they generate. Physiological monitoring (of oxygen consumption, heart rate or blood lactate concentration) provides objective measures of training intensity, and direct observation gives valid measures of most aspects of training; however, these methods are impractical for continuous, long term use. Coaches and athletes quantify training for purposes of motivation, systematisation of training and training prescription, but there has been little study of the use of training quantification by these practitioners. Motivation and systematisation are probably achieved best with diaries. Direct observation appears to be the best method of ensuring compliance with a training prescription, although heart rate monitoring is also a promising method for prescribing endurance training intensity. Sport scientists quantify training to study its effects on the performance and health status of competitive athletes. Most studies have been descriptive rather than experimental, and unvalidated questionnaires have been the predominant method of assaying training. The main areas of research include performance prediction and enhancement, overtraining, reproductive dysfunction, injury, illness, and nutritional status. Training has substantial effects in all of these areas. There is a need for more experimental studies that utilise validated measures of training to investigate how to reduce sports injuries and enhance competitive sports performance. More attention could also be given to methodological issues of training quantification.

The effects of acute and chronic exercise on immunoglobulins

Abstract: The effects of acute exercise (both graded-maximal and submaximal) and exercise training on resting immunoglobulin levels and immunoglobulin production are reviewed. Brief graded-maximal or intensive short term submaximal exercise tends to be associated with increases in serum immunoglobulins, the pattern of which does not vary between athletes and nonathletes. Plasma volume changes appear to largely explain these acute increases. Acute moderate exercise, such as a 45-minute bout of walking, on the other hand, has been associated with a transient rise in serum immunoglobulin levels despite no change in plasma volume. This increase is probably the result of contributions from extravascular protein pools and an increased lymph flow. Total serum immunoglobulin changes following less than 40 km of running are minor and/or statistically insignificant, although the concentration of IgG is observed to be at its lowest by 1.5 hours after exercise. The greatest effect of acute submaximal exercise appears to be on serum IgM levels which tend to increase, although results are somewhat inconsistent. Various mechanisms of stimulation have been proposed to explain the exercise-induced effect on IgM, which is the first antibody class produced in an immune response. These mechanisms include nonspecific noradrenergic sympathetic neural interactions with the immune system and the possibility of antigen stimulation through greater-than-normal quantities of microorganisms entering the body through both increased ventilation rates and breakdown of natural mucosal immunity by drying of airway secretions. When athletes run 45 to 75 km at high intensities, serum immunoglobulin levels have been reported to be depressed for up to 2 days. Thus intense ultramarathon running may lead to greater and longer lasting decreases in serum immunoglobulin levels than following exercise of shorter duration. IgA and IgG, immunoglobulins commonly found in airway and alveolar space secretions, may have diffused from the serum during recovery from prolonged endurance exercise nonspecifically and/or in response to microbial agents and antigens introduced into the airways during the exercise bout. It has been well established that prolonged endurance exercise is associated with muscle cell damage and local inflammation. It has been hypothesised that natural (IgM) autoantibodies may be used to assist macrophages in disposal of muscle cell breakdown products. This could occur either by IgM binding to breakdown products present in the blood, followed by their clearance from the circulation, or it is possible that these antibodies may leave the circulation to carry out this same function in tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasma glucose metabolism during exercise in humans.

Abstract: Plasma glucose is an important energy source in exercising humans, supplying between 20 and 50% of the total oxidative energy production and between 25 and 100% of the total carbohydrate oxidised during submaximal exercise. Plasma glucose utilisation increases with the intensity of exercise, due to an increase in glucose utilisation by each active muscle fibre, an increase in the number of active muscle fibres, or both. Plasma glucose utilisation also increases with the duration of exercise, thereby partially compensating for the progressive decrease in muscle glycogen concentration. When compared at the same absolute exercise intensity (i.e. the same VO2), reliance on plasma glucose is also greater during exercise performed with a small muscle mass, i.e. with the arms or just 1 leg. This may be due to differences in the relative exercise intensity (i.e. the %VO2peak), or due to differences between the arms and legs in their fitness for aerobic activity.

Injuries to the posterior cruciate ligament of the knee

Abstract: The posterior cruciate ligament (PCL) is the strongest ligament about the knee and is approximately twice as strong as the anterior cruciate ligament. Its main function is to prevent the posterior dislocation of the tibia in relation to the femur, providing 95% of the strength to resist the tibial posterior displacement. Along with the anterior cruciate ligament (ACL) the PCL controls the passive ‘screw home’ mechanism of the knee in terminal knee extension. It also provides mechanical support for the collateral ligaments during valgus or varus stress of the knee.

Potassium Regulation during Exercise and Recovery

Abstract: The concentrations of extracellular and intracellular potassium (K+) in skeletal muscle influence muscle cell function and are also important determinants of cardiovascular and respiratory function.

The 'athletic heart syndrome'. A critical review.

Abstract: Cardiological findings in athletes are often similar to those observed in clinical cases. Electrocardiographic and cardiac imaging abnormalities as well as physical findings may be the same in both of these groups. Bradycardia and rhythm disturbances are the most common abnormalities in athletes. Most athletes with abnormal electrocardiograms are asymptomatic and numerous investigators have failed to detect heart disease in association with such electrocardiograms. In contrast to cardiac dysfunction observed in clinical cases, enhanced or normal ventricular systolic and diastolic function have been reported in athletes. In endurance athletes, this is associated with very high values for maximal aerobic power (VO2max).

Fluid replacement and exercise stress. A brief review of studies on fluid replacement and some guidelines for the athlete.

Abstract: Fluid ingestion during exercise has the twin aims of providing a source of carbohydrate fuel to supplement the body's limited stores and of supplying water and electrolytes to replace the losses incurred by sweating. Increasing the carbohydrate content of drinks will increase the amount of fuel which can be supplied, but will tend to decrease the rate at which water can be made available; where provision of water is the first priority, the carbohydrate content of drinks will be low, thus restricting the rate at which substrate is provided. The composition of drinks to be taken will thus be influenced by the relative importance of the need to supply fuel and water, this in turn depends on the intensity and duration of the exercise task, on the ambient temperature and humidity, and on the physiological and biochemical characteristics of the individual athlete. Carbohydrate ingested during exercise appears to be readily available as a fuel for the working muscles, at least when the exercise intensity does not exceed 70 to 75% of maximum oxygen uptake. Carbohydrate-containing solutions appear to be more effective in improving performance than plain water. Water and electrolytes are lost form the body in sweat: although the composition of sweat is rather variable, it is invariably hypotonic with respect to plasma. Sweat rate is determined primarily by the metabolic rate and the environmental temperature and humidity. The sweat rate may exceed the maximum rate of gastric emptying of ingested fluids, and some degree of dehydration is commonly observed. Excessive replacement of sweat losses with plain water or fluids with a low sodium content may result in hyponatraemia. Sodium replacement is essential for postexercise rehydration. The optimum frequency, volume and composition of drinks will vary widely depending on the intensity and duration of the exercise, the environmental conditions and the physiology of the individual. The athlete must determine by trial and error the most suitable regimen.

The role of exercise in weight regulation in nonathletes.

Abstract: Obesity is an extremely prevalent condition that is associated with a range of deleterious health effects. While traditionally considered a disorder primarily of energy intake, accumulating evidence underscores the importance of energy expenditure in the development and treatment of obesity. As the most variable component of energy expenditure, physical activity can influence the development of obesity as well as success in achieving both initial and long term weight loss. Among the types of exercise-related physiological and behavioural factors most likely to be involved in the development of obesity are reductions in the amount of physical activity actually performed, differences in the effect of physical activity on diet-induced thermogenesis, and modeling of deleterious dietary and exercise patterns on the part of the family and other facets of the environment. In contrast, there is relatively little evidence supporting the common belief that obese individuals have a significantly greater energy intake than nonobese individuals. With respect to weight reduction in the already obese, while increased physical activity levels often augment caloric restriction programmes in aiding initial weight loss, evidence suggests that physical activity may be particularly important in helping to sustain initial losses through increased total energy output, preservation of lean body mass, and changes in substrate utilisation. The psychological benefits received from regular participation in a physical activity programme may serve as an additional impetus for engaging in such activities over the long run. Developing programmes to aid in long term adherence to physical activity regimens remains the most critical challenge. Recent results suggest the utility of regular, brief contacts in aiding sustained physical activity participation in individuals attempting to control their weight.

Physiology of Exercise in the Cold

Abstract: Recreational and job requirements have increased the incidence in which humans exercise in cold environments. Understanding the physiological responses while exposed to cold entails knowledge of how exercise and cold interact on metabolic, cardiopulmonary, muscle and thermal aspects of human performance. Where possible, distinctions are made between responses in cold air and cold water.

Enhancement of athletic performance with drugs. An overview.

Abstract: Drug use among athletes has become a recognised problem in sports. Athletes may use drugs for therapeutic indications, for recreational or social reasons, as ergogenic aids or to mask the presence of other drugs during drug testing. Stimulants were some of the first drugs used and studied as ergogenic aids. Amphetamines may increase time to exhaustion by masking the physiological response to fatigue. Caffeine may improve utilisation of fatty acids as a fuel source thereby sparing muscle glycogen. Cocaine and other sympathomimetic drugs have little or no effect on athletic performance. Anabolic steroids appear to have the potential to increase lean muscle mass and strength under certain conditions. Human growth hormone may also be used for an anabolic effect, but data on this effect are lacking. Erythropoietin may represent a pharmacological alternative to blood doping by increasing red blood cell mass. The use of narcotic analgesics is not necessarily ergogenic but can be harmful if used to allow participation of an athlete with a severe injury. According to the American College of Sports Medicine alcohol does not possess an ergogenic effect. However, it may be used to reduce anxiety or tremor prior to competition. Marijuana does not increase strength. Tobacco products may produce psychomotor effects or control appetite which may be beneficial to some athletes. Other drugs used by athletes include β-blocking agents, diuretics, and a variety of nutritional supplements. In addition, diuretics and probenecid may be taken to mask drug contents in the urine. Whether the ergogenic effects are real or perceived, the potential for adverse effects exists for all of these drugs. Potential health complications represent a serious risk to an otherwise healthy population. Further research on the long term health risks in athletes taking ergogenic drugs is needed.

Common American Football Injuries

Abstract: As many as 1.5 million young men participate in American football in the United States. An estimated 1.2 million football-related injuries are sustained annually. Since the 1970s epidemiological studies have shown that the risk of injury is higher in older athletes and lower in teams with more experienced coaches and more assistant coaches. 51% of injuries occurred at training; contact sessions were 4.7 times more likely to produce injuries than controlled sessions. Injury rates were reduced by wearing shorter cleats and preseason conditioning.

The impact of exercise and diet restriction on daily energy expenditure

Abstract: In addition to the direct energy cost of physical activity, exercise may influence resting energy expenditure in 3 ways: (a) a prolonged increase in postexercise metabolic rate from an acute exercise challenge; (b) a chronic increase in resting metabolic rate associated with exercise training; and (c) a possible increase in energy expenditure during nonexercising time. It seems apparent that the greater the exercise perturbation, the greater the magnitude of the increase in postexercise metabolic rate. An exercise prescription for the general population that consists of exercise of low (less than 50% VO2max) or moderate intensity (50 to 75% VO2max) does not appear to produce a prolonged elevation of postexercise metabolic rate that would influence body-weight. Inconsistent results have been found with respect to the effects of exercise training and the trained state on resting metabolic rate. Whereas some investigators have found a higher resting metabolic rate in trained than untrained individuals and in individuals after an exercise training programme, other investigators have found no chronic exercise effect on resting metabolic rate. Differences in experimental design, genetic variation and alterations in energy balance may contribute to the discrepant findings among investigators. A relatively unexplored area concerns the influence of exercise training on energy expenditure during nonexercising time. It is presently unclear whether exercise training increases or decreases the energy expenditure associated with spontaneous or nonpurposeful physical activity which includes fidgeting, muscular activity, etc. The doubly labelled water technique represents a methodological advance in this area and permits the determination of total daily energy expenditure. Concomitant with the determination of the other components of daily energy expenditure (resting metabolic rate and thermic effect of a meal), it will now be possible to examine the adaptive changes in energy expenditure during nonexercising time. A plethora of studies have examined the combined effects of diet and exercise on body composition and resting metabolic rate. The hypothesis is that combining diet and exercise will accelerate fat loss, preserve fat-free weight and prevent or decelerate the decline in resting metabolic rate more effectively than with diet restriction alone. The optimal combination of diet and exercise, however, remains elusive. It appears that the combination of a large quantity of aerobic exercise with a very low calorie diet resulting in substantial loss of bodyweight may actually accelerate the decline in resting metabolic rate. These findings may cause us to re-examine the quantity of exercise and diet needed to achieve optimal fat loss and preservation of resting metabolic rate.

Sports injuries and oral contraceptive use. Is there a relationship

Abstract: Unlike men women experience a regular endocrine cycle each month. Some research indicates that physical efficiency in women may be low premenstrually. Further hormonal fluctuations may increase the risk of injury during the menstrual cycle. In addition the risk of injury increases in the period prior to menopause. Since oral contraceptives (OCs) suppress activities of the pituitary gland hormonal changes in the menstrual cycle are altered which may in turn reduce the risk of injury. Moreover since women athletes often experience amenorrhea or oligomenorrhea OCs may prevent bone loss which is common in amenorrheic or oligomenorrheic women. Thus Ocs would likely result in less bone stress and traumatic fractures as experienced by women athletes who are amenorrheic or oligomenorrheic and do not take OCs. Further a study in Sweden shows that women soccer athletes who used OCs experienced significantly fewer traumatic sports injuries than nonusers (51.5% vs. 88.2%). Moreover menstrual blood loss is minimal in women taking OCs and the hemoglobin level is higher than that of nonusers. In addition anaerobic working time for muscles increases muscle injuries. So optimal oxygen transport in OC users provides more aerobic working time for muscles which should benefit physical performance. Pregnant women experience higher levels of estrogen than do nonpregnant women. These higher levels influence ligament laxity. So if women athletes especially gymnasts increase their estrogen levels by taking OCs they could in theory improve ligament laxity and joint capsules. Not enough studies have been conducted to substantiate these theories however. Further research is encouraged.

Impact of reduced training on performance in endurance athletes.

Abstract: Many endurance athletes and coaches fear a decrement in physical conditioning and performance if training is reduced for several days or longer. This is largely unfounded. Maximal exercise measures (VO2max, maximal heart rate, maximal speed or workload) are maintained for 10 to 28 days with reductions in weekly training volume of up to 70 to 80%. Blood measures (creatine kinase, haemoglobin, haematocrit, blood volume) change positively or are maintained with 5 to 21 days of reduced training, as are glycogen storage and muscle oxidative capacities. Submaximal exercise measures (economy, heart rate, postexercise lactate) and muscular power are maintained or improved with a 70 to 90% reduction in weekly volume over 6 to 21 days, provided that exercise frequency is reduced by no more than 20%. Athletic performance is improved or maintained with a 60 to 90% reduction in weekly training volume during a 6 to 21 day reduced training period, primarily due to an enhanced ability to exert muscular power. These findings suggest that endurance athletes should not refrain from reduced training prior to competition in an effort to improve performance, or for recovery from periods of intense training, injury, or staleness.