ISSN:0112-1642    

DOI:10.2165/00007256-198502030-00001

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe belief among athletes that caffeine is an ergogenic aid is common, and several governing bodies of sport have barred use of the drug during competition. At the cellular level, caffeine has been implicated to affect the translocation of calcium in muscle, promote an increase in cellular levels of cyclic AMP and cause a blockade of adenosine receptors in the central nervous system. The general systemic effect of caffeine is to cause central nervous system arousal, mobilisation of free fatty acids and other metabolites, and possibly enhance the contractile status of muscle.At present, the scientific community remains divided as to whether caffeine ingestion will indeed produce an ergogenic effect upon sport performance. Some evidence suggests that caffeine may improve performance in events relying upon strength and power; however, the lack of in vivo research in humans makes it difficult to form firm conclusions. In addition, reports concerning caffeine’s effect on V̇O2 maxand performance during incremental exercise are not in agreement.On the other hand, recent studies suggest that caffeine might indeed have ergogenic potential in endurance events (e.g. marathon running). It is hypothesised that the mechanism behind these findings is related to the increased availability of free fatty acids for muscle metabolism which has a glycogen-sparing effect.

ISSN:0112-1642    

DOI:10.2165/00007256-198502030-00002

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe inter-relationship of food and physical performance, food is considered as a conglomerate of nutrients and man is depicted as a kind of organic pudding. This ‘machine’ concept of human performance in combination with the mysticism surrounding vitamins, has led to the faddish belief that additional vitamins are necessary to improve physical performance by means of supercharging the metabolic processes in the body.Various vitamins and their dietary recommendations as well as the indicators for vitamin status are discussed. It is concluded that a marginal or subclinical deficiency state can be defined as an intermediate between optimal vitamin status and frank clinical deficiency. Marginal deficiency is characterised by biochemical values deviating from statistically derived reference limits as well as the absence of clinical signs and symptoms of vitamin deficiency.Besides the static, mostly biochemical, indicators of vitamin status, more functional indicators are considered, among them work capacity. An extensive historical review on depletion studies, epidemiological surveys and supplementation studies is presented.It is concluded that a restricted intake of some B-complex vitamins — individually and in combination — of approximately less than 35 to 45 % of the recommended dietary allowance may lead to decreased endurance capacity within a few weeks. Studies on ascorbic acid (vitamin C) depletion and fat-soluble vitamin A deficiency have noted no decrease of endurance capacity. However, in a few recent epidemiological surveys, biochemical vitamin C deficiency was actually shown to decrease aerobic power.Although the general conclusion is that a reduced water-soluble vitamin intake decreases endurance capacity, it is believed that further controlled experimentation is needed with B-complex vitamins and vitamin C individually. Furthermore, usually employed reference limits for vitamins need reappraisal translating them into impairment limits.With respect to the available evidence, it can be concluded that supplementation of diet with either single or multivitamin preparations containing B-complex vitamins, vitamin C or E does not improve physical performance in athletes with a normal biochemical vitamin balance resulting from a well-balanced diet.Although vitamin supplementation does not seem to produce any effect when the diet is adequate, it is possible that vitamin B-complex supplementation is useful in sports with a high energy expenditure, because of the unavoidable consumption of ‘empty calories’ i.e. food products with a low nutrient density.The side effects of megavitamin supplementation are discussed briefly.

ISSN:0112-1642    

DOI:10.2165/00007256-198502030-00003

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe study of human performance and perceived exertion during physical activity has been an area of considerable interest and research for over 50 years. This review considers the evidence of many investigators who have been researching the physiological basis as well as non-physiological basis for the ratings of perceived exertion.During low levels of activity, physical perception in the working muscles appears to be the primary stimulus for effort perception. When work intensity exceeds the lactate threshold, incremental elevations in blood lactate complement peripheral input from the neuro-muscular mechanisms. Once a critical absolute ventilatory threshold is reached, central input also contributes to effort perception. In most instances, peripheral input predominates over central cues, although it has been shown that pronounced central cues may dominate the perception of effort. Central (heart rate,V̇E,V̇O2) or local (muscle and blood lactate, adenosine triphosphate, creatine phosphokinase, glycogen) cues highlighted in these studies demonstrate both the complexity of effort perception, and the need for better understanding of the physiological components upon which it is based. Athletes have been shown to have a greater tendency to reduce perceptual ratings than their non-active counterparts. In view of these observations, it is apparent that a theoretical framework based upon physiological and psychological considerations may exist to support the concept of training-induced alterations in perceived exertion. This appears to be particularly true in higher ranges of exercise intensity. Part of the problem in reaching a conclusion on the issue of perceptual ratings trainability centres upon the agreement on what should be recognised as a significant decrement in perceived exertion.It is concluded that there is considerable variation in the findings of the literature and that any reported variations in performance may well be greatly influenced by intersubject variability, the type of exercise, and nutritional status of subject. Further research is required to understand this issue better.

ISSN:0112-1642    

DOI:10.2165/00007256-198502030-00004

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe effects of exercise training on energy expenditure, energy intake, fat cell size and adipose tissue lipolysis have been reviewed. Individuals engaged in regular and intense training programmes, e.g. long distance runners, seem to exhibit an elevated resting metabolic rate but moderate training is not accompanied by any important change. Diet-induced thermogenesis is a significant component of daily energy expenditure. It is still unclear whether or not exercise or training causes significant alteration in the thermic response to food intake. Energy expenditure associated with physical activity can play a meaningful role in body composition and adipose tissue metabolism. Largest weight losses have been achieved with programmes of long duraticu, presumably without marked compensation in food intake. However, it has been shown repeatedly that an increase in energy expenditure with exercise training tends to be associated with an elevation in food intake in free-living individuals. Weight loss is concomitant with a reduction in fat cell diameter and, when caused by an exercise training programme, it is generally accompanied by an increase in fat cell lipolytic activities. There are clear indications that weight loss induced by exercise training has a much higher fat content than the weight loss caused by dieting. In addition, data suggest that exercise training may result in a greater depletion of fat stores than a low calorie diet, thus delaying the advent of the resistance phase to fat loss. Data on human subjects derived from well controlled energy balance and metabolic experiments are needed to further advance our understanding about the effects of exercise training on the adipose tissue.

ISSN:0112-1642    

DOI:10.2165/00007256-198502030-00005

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

ISSN:0112-1642    

DOI:10.2165/00007256-198502030-00006

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS