摘要:

Studies addressing children's perceptions of exercise effort have appeared steadily in the scientific literature over the last 20 years, though they have been relatively sparse in number. With little or no regard for their suitability, researchers initially applied to children the methods and applications of the rating of perceived exertion (RPE) notion established amongst adults. Whilst some success was claimed, findings were inconclusive, possibly because of the use of an inappropriate measurement scale. More recently, the development of the child-specific Children's Effort Rating Table (CERT) has advanced research in this domain and helped to focus attention on the numerous problems of applying this psychophysical concept to such immature subjects. Accordingly, the scope for further research in this discipline is now far broader than ever before.

ISSN:0112-1642    

出版商:ADIS    

年代:1997

数据来源: ADIS

摘要:

The increase in ventilation caused by exercise is controlled by a combination of neural and chemical events, although the precise contribution and relative importance of these signals is still debated. It is generally agreed that the genesis of exercise hyperpnoea lies within the central nervous system and that peripheral reflexes, both chemical and neural, modulate central drive. Recently, attention has once again focused on the idea that circulating factors, in particular potassium, may play an important role in this modulation by stimulating known areas of peripheral chemoreception. Arterial chemoreceptors, muscle chemoreflex and slowly adapting pulmonary stretch receptors are all excited by hyperkalaemia. When potassium is raised to mimic exercise concentrations it increases ventilation in anaesthetised animals. This response is abolished by surgical denervation of the arterial chemoreceptors and is markedly reduced by chemical denervation with hyperoxia. Hypoxia enhances the ventilatory response to hyperkalaemia, and the stimulatory effects of potassium are further increased when combined with lactic acid or raised concentrations of noradrenaline. Hyperkalaemia can also increase the hypoxic sensitivity of the arterial chemoreflex in exercise. There is a close temporal relationship between potassium and ventilation during exercise, but changes in potassium are not proportionally related to changes in ventilation. When all data are taken together, there is good evidence that potassium has a supporting role in the control of exercise hyperpnoea, predominantly through modulation of the arterial chemoreflex.

ISSN:0112-1642    

出版商:ADIS    

年代:1997

数据来源: ADIS

摘要:

It is widely documented that athletes should consume carbohydrates prior to, during and after exercise. Ingestion of carbohydrates at these times will optimise performance and recovery. In spite of this knowledge, there is a paucity of information available to athletes concerning the types of carbohydrate foods to select. Therefore, it is suggested that the glycaemic index may be an important resource when selecting an ideal carbohydrate. The glycaemic index categorises foods containing carbohydrates according to the blood glucose response that they elicit. Carbohydrate foods evoking the greatest responses are considered to be high glycaemic index foods, while those producing a relatively smaller response are categorised as low glycaemic index foods.Athletes wishing to consume carbohydrates 30 to 60 minutes before exercise should be encouraged to ingest low glycaemic index foods. Consuming these types of foods will decrease the likelihood of creating hyperglycaemia and hyperinsulinaemia at the onset of exercise, while providing exogenous carbohydrate throughout exercise. It is recommended that high glycaemic index foods be consumed during exercise. These foods will ensure rapid digestion and absorption, which will lead to elevated blood glucose levels during exercise. Post-exercise meals should consist of high glycaemic index carbohydrates. Low glycaemic foods do not induce adequate muscle glycogen resynthesis compared with high glycaemic index foods.

ISSN:0112-1642    

出版商:ADIS    

年代:1997

数据来源: ADIS

摘要:

Physical training and heat acclimation are both commonly adopted tactics to improve performance and/or tolerance times when individuals must compete or work in the heat. Potential benefits include: (i) improved aerobic fitness and thus a greater cardiovascular reserve (probably seen mainly after training); (ii) a lower resting body temperature that allows greater heat storage (probably seen mainly after acclimation); (iii) a decreased energy cost of a given intensity of exercise (seen after acclimation and also as the learning component of training); (iv) an enhanced sweating response at a given percentage of maximal effort (probably developed by both treatments); (v) a slower increase in body temperature owing to (iii) and/or (iv) [seen after both treatments]; (vi) a reduced cardiovascular stress because of changes in the autonomic nervous system (probably realised mainly by training), expansion of blood volume (seen after both treatments) and/or a decreased peripheral pooling of blood (probably found after both treatments); and (vii) improved subjective tolerance reflecting a decrease in the relative intensity of a given activity (probably seen mainly after training), a reduction in the physiological strain (found after both treatments) and/or habituation to heat-exercise stress (probably developed by both treatments). Factors affecting improvements in physiological and psychological responses to a given set of conditions include: (i) the individual's initial fitness and acclimatisation to heat; (ii) age, gender, hydration, sleep deprivation, circadian rhythms and in women the menstrual cycle; (iii) use of ergogenic aids such as fluid ingestion, carbohydrate and/or electrolyte replacement and blood doping; (iv) event or test conditions such as the mode of exercise, the severity of environmental heat stress and the type of clothing worn; and (v) treatment conditions such as the intensity, duration and frequency of exercise and/or heat exposure, the length of any rest intervals and cumulative depletion of body water and minerals.

ISSN:0112-1642    

出版商:ADIS    

年代:1997

数据来源: ADIS