ISSN:0112-1642    

DOI:10.2165/00007256-198502010-00001

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThermoregulation is an important consideration not only for athletic performance but also for the safety of the athlete. This article presents a broad overview of the mechanisms by which body heat is dissipated in an individual exercising in a hot environment. Particularly emphasised are more recent views of body heat loss mechanisms and the influences of non-thermal inputs, such as effects due to changing blood volume or blood flow distribution.During exercise in a hot environment, metabolic heat produced by the exercising muscles is transported by the circulating blood to the surface of the body where it is released to the environment, either by radiation and convection or by evaporation of sweat. The primary drives for both the increased skin blood flow and increased body sweating are the thermal inputs which are sensed by receptors in the deep body core, with a lesser drive from skin receptors. These thermal signals are integrated in the hypothalamus and proper heat loss responses are effected. When exercise is prolonged, however, and body rehydration is not adequate, the total blood volume may be compromised. In addition, as the core temperature increases during exercise, larger proportions of the blood volume are distributed to the cutaneous vessels, thus effectively reducing cardiac return and central blood volume. During severe exercise, a reduction in cardiac filling may result in a fall in central venous pressure and stimulate baroreceptor vasconstrictor reflexes. As discussed below, the outputs from these baroreceptors compete with and modify the thermal drives for both the control of the skin blood flow and control of the sweat glands.The effect of high ambient temperatures on exercise performance is most evident in prolonged submaximal exercise. Normally, maximal exercise performance is not altered by high temperatures unless the individual has an elevated deep body temperature before the start of the exercise task. However, submaximal exercise performance is often impaired by high ambient temperatures, but may be improved by programmes of physical training and heat acclimatisation. Both training and heat acclimatisation significantly modify the control systems which regulate skin blood flow and sweating. Only acclimatisation programmes, however, are effective in preventing heat stress during prolonged exercise in hot environments.

ISSN:0112-1642    

DOI:10.2165/00007256-198502010-00002

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryInjuries to the hamstring muscles can be devastating to the athlete because these injuries frequently heal slowly and have a tendency to recur. It is thought that many of the recurrent injuries to the hamstring musculotendinous unit are the result of inadequate rehabilitation following the initial injury. The severity of hamstring injuries is usually of first or second degree, but occasionally third-degree injuries (complete rupture of the musculotendinous unit) do occur.Most hamstring strain injuries occur while running or sprinting. Several aetiological factors have been proposed as being related to injury of the hamstring musculotendinous unit. They include: poor flexibility, inadequate muscle strength and/or endurance, dyssynergic muscle contraction during running, insufficient warm-up and stretching prior to exercise, awkward running style, and a return to activity before complete rehabilitation following injury.Treatment for hamstring injuries includes rest and immobilisation immediately following injury and then a gradually increasing programme of mobilisation, strengthening, and activity. Permission to return to athletic competition should be withheld until full rehabilitation has been achieved (complete return of muscle strength, endurance, and flexibility in addition to a return of co-ordination and athletic agility). Failure to achieve full rehabilitation will only predispose the athlete to recurrent injury. The best treatment for hamstring injuries is prevention, which should include training to maintain and/or improve strength, flexibility, endurance, co-ordination, and agility.

ISSN:0112-1642    

DOI:10.2165/00007256-198502010-00003

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe role of ammonia in exercise-induced fatigue is reviewed. Implications for integrated activity of developing hyperammoneic states, caused by various precipitating conditions such as exercise, liver dysfunction, hypoxia, hyperoxia, and chemical poisoning are described.The central role of ammonia in diverse important metabolic pathways indicates its ubiquitous role in a spectrum of activity ranging from elite exhaustive performance of sportsmen and -women to life-threatening organ dysfunction. The action of ammonia and metabolites from associated pathways in producing seemingly dangerous short term conditions, but inducing possible long term protection against degenerative processes associated with ageing (free radical-induced cellular damage) indicate the paradoxical position of ammonia and its associated metabolic pathways for health and disease processes.

ISSN:0112-1642    

DOI:10.2165/00007256-198502010-00004

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryAlthough participation in many sporting activities has increased dramatically in recent years, the study of injuries sustained during training or participation is still in its infancy.The most commonly used strategy is to describe the characteristics of a suitable case-series. This approach is relatively easy to implement, can be used to estimate the total morbidity load in a population, and can identify the relative frequency of various types of injury. However, the case series method cannot validly identify risk factors for injury or athletes at high risk; similarly, it cannot be used to estimate the absolute level of risk associated with sports participation. Finally, the population from which the injuries arose is often difficult to identify, and the series may not be representative of all injuries occuring in that population, and this may produce quite misleading results.In contrast, a variety of epidemiological designs may be employed to address questions of aetiology and to identify high risk groups of athletes. With careful attention to the underlying population denominators, one may estimate the relative or absolute risk of injury for athletes with given risk characteristics, defined by type and intensity of their participation in sports or by their individual physiology. This is achieved by inclusion of suitable control subjects in the epidemiological sample; these controls may be uninjured athletes or random samples of the general population. The comparison of injured and uninjured groups permits valid inferences to be drawn concerning risk factors, avoiding the many potential biases which affect inferences drawn from injured athletes only.

ISSN:0112-1642    

DOI:10.2165/00007256-198502010-00005

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe winter athlete has several potential tactics for sustaining body temperature in the face of severe cold. An increase in the intensity of physical activity may be counter-productive because of increased respiratory heat loss, increased air or water movement over the body surface, and a pumping of air or water beneath the clothing. Shivering can generate heat at a rate of 10 to 15 kJ/min, but it impairs skilled performance, while the resultant glycogen usage hastens the onset of fatigue and mental confusion.Non-shivering thermogenesis could arise in either brown adipose tissue or white fat. Brown adipose tissue generates heat by the action of free fatty acids in uncoupling mitochondrial electron transport, and by noradrenaline-induced membrane depolarisation and sodium pumping. The existence of brown adipose tissue in human adults is controversial, and although there are theoretical mechanisms of heat production in white fat, their contribution to the maintenance of body temperature is small.Acclimatisation to cold develops over the course of about 10 days, and in humans the primary change is an insulative, hypothermic type of response; this reflects the intermittent nature of most occupational and athletic exposures to cold. Nevertheless, with more sustained exposure to cold air or water, humans can apparently develop the humoral type of acclimatisation described in small mammals, with an increased output of noradrenaline and/or thyroxine.The associated mobilisation of free fatty acids suggests the possibility of using winter sport as a pleasant method of treating obesity. In men, a combination of moderate exercise and facial cooling induces a substantial fat loss over a 1- to 2-week period, with an associated ketonuria, proteinuria, and increase of body mass. Possible factors contributing to this fat loss include: (a) a small energy deficit; (b) the energy cost of synthesising new lean tissue; (c) energy loss through the storage and excretion of ketone bodies; (d) catecholamine-induced ‘futile’ metabolic cycles with increased resting metabolism; and (e) a specific reaction to cold dehydration.Current limitations for the clinical application of such treatment include uncertainty regarding optimal environmental conditions, concern over possible pathological reactions to cold, and suggestions of a less satisfactory fat mobilisation in female patients.Possible interactions between physical fitness and metabolic reactions to cold remain controversial. However, it is clear that short term cold exposure induces a modest increase of physical working capacity. Long term effects of cold upon fitness are probably mediated largely through associated changes in habitual physical activity.

ISSN:0112-1642    

DOI:10.2165/00007256-198502010-00006

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

ISSN:0112-1642    

DOI:10.2165/00007256-198502010-00007

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS