ISSN:1066-7814    

DOI:h2001-035

出版商:NRC Research Press    

年代:2001

数据来源: NRC

摘要:

Strenuous physical exercise represents a condition that is often associated with increased production of reactive oxygen species in various tissues. One of the most reliable indices of exercise-induced oxidant production is tissue glutathione oxidation. In humans, exerciseinduced blood glutathione oxidation is rapid and subject to control by antioxidant supplementation. The objective of this brief review is to provide an update of our current understanding of cellular thiols and thiol antioxidants. Cellular thiols are critically important in maintaining the cellular antioxidant defense network. In addition, thiols play a key role in regulating redox-sensitive signal transduction process. Lipoic acid is a highly promising thiol antioxidant supplement. Recent studies have clarified that while higher levels of oxidants may indeed inflict oxidative damage, oxidants are not necessarily deleterious. Under certain conditions oxidants may function as cellular messengers that regulate a multitude of signal transduction pathways. In light of this, the significance of oxidants in various aspects of biology needs to be revisited.

ISSN:1066-7814    

DOI:h2001-037

出版商:NRC Research Press    

年代:2001

数据来源: NRC

摘要:

Magnesium, zinc and chromium are mineral elements required in modest amounts for health and optimal performance. Accumulating evidence supports the hypothesis that magnesium and zinc play significant roles in promoting strength and cardiorespiratory function in healthy persons and athletes. Differences in study designs, however, limit conclusions about recommendations for intakes of magnesium and zinc needed for optimal performance and function. The role of chromium in supporting performance is not well established. There is a compelling need to confirm and extend findings of beneficial effects of magnesium and zinc function and performance of humans. Suggestions for an experimental model and specific topics for research to advance knowledge of mineral nutrition to promote attainment of genetic potential for optimal performance are provided.

ISSN:1066-7814    

DOI:h2001-038

出版商:NRC Research Press    

年代:2001

数据来源: NRC

摘要:

Strenuous prolonged exertion and heavy training are associated with depressed immune function. Furthermore, improper nutrition can compound the negative influence of heavy exertion on immunocompetence. Dietary deficiencies of protein and specific micronutrients have long been associated with immune dysfunction. An adequate intake of iron, zinc, and vitamins A, E, B6 and B12 is particularly important but excess intakes can also impair immune function. Immune system impairment has also been associated with excess intake of fat. To maintain immune function, athletes should eat a well balanced diet sufficient to meet their energy requirements. An athlete exercising in a carbohydrate-depleted state experiences larger increases in circulating stress hormones and a greater perturbation of several immune function indices. Conversely, consuming carbohydrate during exercise attenuates rises in stress hormones such as cortisol and appears to limit the degree of exercise-induced immunosuppression, at least for non-fatiguing bouts of exercise. Strong evidence that high doses of antioxidant vitamins, glutamine supplementation or echinacea extracts can prevent exercise-induced immunosuppression is lacking.

ISSN:1066-7814    

DOI:h2001-039

出版商:NRC Research Press    

年代:2001

数据来源: NRC

摘要:

Heavy sports training schedules and competition is often associated with immuno-suppression, and so there is a theoretical justification for providing athletes with nutrients that display immuno-regulatory properties. Among such immuno-nutrients, considerable attention has been paid in recent years to two amino acids, arginine (ARG) and glutamine (GLN). ARG and GLN availability regulate the function ofT lymphocytes, macro phages and polymorphonuclear cells. ARG acts through nitric oxide and polyamine synthesis. The mechanism of action of GLN in immune cells remains unclear. Experience in clinical nutrition suggests that an ARG-enriched diet may limit infectious morbidity in critically ill patients. Data concerning oral/enteral GLN supplementation are more controversial. There have been few trials of supplementation in sports medicine, but results are promising, justifying further studies in which dosages and administration schedules should be taken into account.

ISSN:1066-7814    

DOI:h2001-040

出版商:NRC Research Press    

年代:2001

数据来源: NRC

摘要:

In contrast to moderate physical activity, prolonged and intensive exertion causes numerous changes in immunity that reflect physiologic stress and suppression, and an increased risk of upper respiratory tract infection. Enzymes in immune cells require the presence of micronutrients, leading to attempts by investigators to alter changes in immunity following heavy exertion through use of nutritional supplements, primarily zinc, dietary fat, vitamin C and other antioxidants, glutamine, and carbohydrate. Except for carbohydrate supplementation, none of these nutrients has emerged as an effective countermeasure to exerciseinduced immunosuppression. Data from several studies of endurance athletes suggest that carbohydrate compared to placebo ingestion is associated with an attenuated cortisol, growth hormone, and epinephrine response to heavy exertion, fewer perturbations in blood immune cell counts, lower granulocyte and monocyte phagocytosis and oxidative burst activity, and a diminished pro- and anti-inflammatory cytokine response. Overall, the hormonal and immune responses to carbohydrate compared to placebo ingestion during intensive exercise suggest that physiologic stress and inflammation are diminished, although clinical significance awaits further research.

ISSN:1066-7814    

DOI:h2001-041

出版商:NRC Research Press    

年代:2001

数据来源: NRC

摘要:

For many years athletes have used carbohydrate loading to enhance endurance performance. This practice has been based on findings demonstrating that 1) exercise induced depletion of the muscle glycogen stores followed by the intake of a carbohydrate rich diet, resulted in muscle glycogen stores above normal values and 2) that the pre-exercise muscle glycogen content was the main determinant of the capacity to perform strenuous exercise to exhaustion. Lately it has been speculated whether a period of a high fat diet, followed by carbohydrate loading to restore or increase muscle glycogen levels above normal, would be of further advantage for exercise performance. From the discussed data it emerges, however, that varying periods offat adaptation followed by a carbohydrate rich diet prior to exercise is of no benefit for exercise performance. Despite an increased fat oxidation and a concomitant decrease in carbohydrate oxidation during submaximal exercise, no benefit in a subsequent time trial appeared. Data suggest that this dietary regimen impairs the ability to utilise carbohydrates.

ISSN:1066-7814    

DOI:h2001-042

出版商:NRC Research Press    

年代:2001

数据来源: NRC

摘要:

The goals of pre-exercise nutritional strategies are to optimise the availability of carbohydrate (CHO) and fluid. Ingestion of CHO 3-4 hr prior to exercise can increase liver and muscle glycogen stores and has been associated with enhanced endurance exercise performance. The metabolic effects of CHO ingestion persist for at least 6 hr. Although an increase in plasma insulin following CHO ingestion in the hour prior to exercise inhibits lipolysis and liver glucose output, and can lead to transient hypoglycemia during subsequent exercise, there is no convincing evidence that this is always associated with impaired exercise performance. Having said that, individual experience should inform individual practice. Interventions to increase plasma FFA availability prior to exercise have been shown to reduce CHO utilisation during exercise, but do not appear to have major ergogenic benefits. It is more difficult to hyperhydrate prior to exercise and although there has been interest in glycerol ingestion, to date research results have been equivocal. At the very least, athletes should ensure euhydration prior to exercise.

ISSN:1066-7814    

DOI:h2001-043

出版商:NRC Research Press    

年代:2001

数据来源: NRC

摘要:

The intake of fluid and CHO offers benefits to the performance of a number of sports events and exercise activities. The effects of dehydration on performance are now well known, with the penalties ranging from subtle, but often important, decrements in performance at low levels of fluid deficit to the severe health risks associated with substantial fluid losses during exercise in the heat. Although evidence of the beneficial effects of CHO intake during exercise have existed for over 70 years, sports scientists are still to discover all the situations in which benefits occur and to explain the mechanisms involved. Optimal strategies for CHO and fluid intake during exercise are yet to be fine-tuned, and ultimately will be determined by practical issues such as the opportunity to eat or drink during an event, and gastrointestinal comfort.

ISSN:1066-7814    

DOI:h2001-044

出版商:NRC Research Press    

年代:2001

数据来源: NRC

摘要:

The effect of oral creatine supplementation on high-intensity exercise performance has been extensively studied over the past ten years and its ergogenic potential in young healthy subjects is now well documented. Recently, research has shifted from performance evaluation towards elucidating the mechanisms underlying enhanced muscle functional capacity after creatine supplementation. In this review, we attempt to summarise recent advances in the understanding of potential mechanisms of action of creatine supplementation at the level of skeletal muscle cells. By increasing intracellular creatine content, oral creatine ingestion conceivably stimulates operation of the creatine kinase (CK)/phosphocreatine (PCr) system, which in turn facilitates muscle relaxation. Furthermore, evidence is accumulating to suggest that creatine supplementation can beneficially impact on muscle protein and glycogen synthesis. Thus, muscle hypertrophy and glycogen supercompensation a1'e candidate factors to explain the ergogenic potential of creatine ingestion. Additional issues discussed in this review are the fibre-type specificity of muscle creatine metabolism, the identification of responders versus non-responders to creatine intake, and the scientific background concerning potential side effects of creatine supplementation.

ISSN:1066-7814    

DOI:h2001-045

出版商:NRC Research Press    

年代:2001

数据来源: NRC