ISSN:0112-1642    

DOI:10.2165/00007256-199315010-00001

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

ISSN:0112-1642    

DOI:10.2165/00007256-199315010-00002

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThree principal cellular mechanisms have been proposed to explain the ergogenic potential of caffeine during exercise: (a) increased myofilament affinity for calcium and/or increased release of calcium from the sarcoplasmic reticulum in skeletal muscle; (b) cellular actions caused by accumulation of cyclic-3′,5′-adenosine monophosphate (cAMP) in various tissues including skeletal muscle and adipocytes; and (c) cellular actions mediated by competitive inhibition of adenosine receptors in the central nervous system and somatic cells. The relative importance of each of the above mechanisms in explainingin vivophysiological effects of caffeine during exercise continues to be debated. However, growing evidence suggests that inhibition of adenosine receptors is one of the most important, if not the most important, mechanism to explain the physiological effects of caffeine at nontoxic plasma concentrations. Numerous animal studies using high caffeine doses have reported increased force development in isolated skeletal muscle in bothin vitroandin situpreparations. In contrast,in vivohuman studies have not consistently shown caffeine to enhance muscular performance during high intensity, short term exercise. Further, recent evidence supports previous work that shows caffeine does not improve performance during short term incremental exercise. Although controversy exists, the major part of published evidence evaluating performance supports the notion that caffeine is ergogenic during prolonged (>30 min), moderate intensity (≈75 to 80% V̇2max) exercise. The mechanism to explain these findings may be linked to a caffeine-mediated glycogen sparing effect secondary to an increased rate of lipolysis.

ISSN:0112-1642    

DOI:10.2165/00007256-199315010-00003

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryThe drag force on a racing shell increases with the square of velocity corresponding to a 3.2 power increase in energy expenditure. However, the metabolic cost increases with only an approximately 2.4 power function of shell velocity. During international races the metabolic cost corresponds to an oxygen uptake of 6.7 to 7.0 L/min over 6.5 min. The relative anaerobic contribution to 6.5 min of ‘all-out’ rowing has not been determined but is estimated to range from 21 to 30%. Because of the large muscle mass involved in rowing, blood variables reach extreme values: adrenaline 19 nmol/L; noradrenaline 74 nmol/L; pH 7.1; and bicarbonate 9.8 mmol/L. Because of the static component of the rowing stroke at the catch, blood pressure increases to near 200mm Hg, and the heart of oarsmen has adapted to this load by increasing wall thickness and internal diameters. The maximal oxygen uptake of oarsmen may reach 6.6 L/min and ventilation 243 L/min. Arterial oxygen tension decreases by 20mm Hg during ‘all-out’ rowing corresponding to a decrease in pulmonary diffusion capacity. A force of approximately 800 to 900N is developed on the oar. Force generation during rowing is relatively slow, 0.3 to 0.4 sec. Oarsmen are strongest in low velocity movement with 70 to 75% slow twitch fibres in skeletal muscle. Data indicate that rowing technique and training may improve explaining why results become approximately 0.7 sec faster per year.

ISSN:0112-1642    

DOI:10.2165/00007256-199315010-00004

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryStudies of the dietary practices of athletes report that nutritional supplements are commonly used. Supplementation practices vary between sports and individual athletes; however, there is evidence that at least some athletes use a large number of supplements concurrently, often in doses that are very high in comparison with normal dietary intakes.In exploring supplementation practices we propose a classification system separating the supplements into dietary supplements and nutritional erogogenic aids. The dietary supplement is characterised as a product which can be used to address physiological or nutritional issues arising in sport. It may provide a convenient or practical means of consuming special nutrient requirements for exercise, or it may be used to prevent/reverse nutritional deficiencies that commonly occur among athletes. The basis of the dietary supplement is an understanding of nutritional requirements and physiological effects of exercise. When the supplement is used to successfully meet a physiological/nutritional goal arising in sport it may be demonstrated to improve sports performance. While there is some interest in refining the composition or formulation of some dietary supplements, the real interest belongs to the use or application of the supplement; i.e. educating athletes to understand and achieve their nutritional needs in a specific sports situation.The sports drink (carbohydrate-electrolyte replacement drink) is a well known example of a dietary supplement. Scientific attitudes towards the sports drink have changed over the past 20 years. Initial caution that carbohydrate-electrolyte fluids compromise gastric emptying during exercise has now been shown to be unjustified. Numerous studies have shown that 5 to 10% solutions of glucose, glucose polymers (maltodextrins) and other simple sugars all have suitable gastric emptying characteristics for the delivery of fluid and moderate amounts of carbohydrate substrate. The optimal concentration of electrolytes, particularly sodium, remains unknown. Most currently available sports drinks provide a low level of sodium (10 to 25 mmol/L) in recognition that sodium intake may promote intestinal absorption of fluid as well as assist in rehydration. The sodium level of commercial oral rehydration fluids (used in the clinical treatment of diarrhoea and dehydration) is higher than that of the present range of sports drinks. However, even if research indicates that intestinal glucose transport is optimally stimulated at higher sodium concentrations, concern for the palatability of sports drinks may impose a lower ceiling for sodium levels. Commercial viability of a sports drink requires that it provide a refreshing and palatable fluid replacement across a wide variety of sports and exercise situations. However, in specific situations, the appropriate use of a drink may offer special advantages in meeting physiological requirements. For example, during endurance and ultraendurance exercise, suitable intake of a sports drink to preserve hydration and to supply additional carbohydrate substrate for glycogen-depleted muscles has been shown to enhance performance. Additionally, the sports drink may provide a special advantage in recovery and rehydration after prolonged exercise, particularly where more rapid restoration of body fluid and fuel levels will enhance performance in future exercise bouts.High carbohydrate liquids at higher concentrations (20 to 25% carbohydrate solutions, typically from maltodextrin sources) represent another type of dietary supplement. These high carbohydrate supplements, often known as ‘carbo-loader’ supplements, have been manufactured to assist athletes in achieving a high carbohydrate intake by overcoming problems of dietary bulk or lack of nutritional knowledge. They may be useful in situations where a short term need for carbohydrate supersedes other nutritional goals, e.g. carbohydrate loading and prolonged competition over successive days. Where long term nutritional goals and requirements for a combination of nutrients need to be addressed, liquid meal supplements provide a low-bulk, nutritionally complete choice. Liquid meal supplements may be useful as a compact nutrient-dense high energy supplement for athletes with high energy requirements, particularly when it is not practical or comfortable to consume solid foods. They may be useful in preparation for exercise, both as a pre-event meal and as a low residue preparation.Athletes who consume low energy intakes and/or restricted food variety may consume sub-optimal intakes of micronutrients, particularly minerals such as iron or calcium. Adequate vitamin and mineral status is a requirement for optimal sports performance, since many of the micronutrients play a key role in exercise metabolism, recovery and adaptation. A heavy exercise programme may increase requirements for some nutrients, including the B-group vitamins and iron. Athletes at high risk of inadequate micronutrient intake or nutritional deficiencies such as iron deficiency should benefit from nutritional counselling. Supplementation may be required in cases of ongoing suboptimal dietary intake, or to rapidly restore a diagnosed nutrient deficiency state. While many athletes regard iron supplements as a low cost ‘safety net’ against iron deficiency, there are many disadvantages to unsupervised long term intake of high doses of iron. The debate surrounding biochemical and haematological markers of optimal iron status remains unresolved. In general, screening and individual treatment of athletes in high-risk groups is preferred to a mass treatment programme.There is a need for nutrition education of athletes to explain the appropriate use of these dietary supplements. In many cases, the information is specific to the individual athlete or sports situation and may require one-to-one counselling. In most situations, the use of the supplement will simply be a part of a larger plan of optimal sports nutrition or the clinical management of a nutritional disorder. Effective education will not only ensure that dietary supplements are used correctly, but will highlight the importance of optimal sports nutrition.

ISSN:0112-1642    

DOI:10.2165/00007256-199315010-00005

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS

摘要:

SummaryOrthotic shoe inserts are very effective in providing symptomatic relief of lower extremity complaints in running athletes. Inserts adjust the biomechanical variables associated with running injuries and reduce the effect of high stresses produced by running activities. Orthotic treatment is based on an understanding of complex coupling of rotation of the lower extremity with pronation and supination of the subtalar joint. Orthotic fabrication is initiated by determining the neutral position of the foot and obtaining an accurate cast of this position.Successful treatment with orthotic shoe inserts is dependent on careful evaluation of the runner and formulation of a properly fitted orthosis. When correctly utilised, orthotic shoe inserts are beneficial for a broad range of disorders experienced by runners. Since biomechanical deficits may be related to injuries along the entire lower extremity, specific diagnoses may be of lesser indication; however, accurate identification of the underlying biomechanical deficit is critical. Problems related to excessive or prolonged pronation are most amenable to orthotic treatment. While treatment of the cavus foot with orthotic shoe inserts is sometimes worthwhile, the clinician should be aware of limited success in this instance.Finally, orthotics are only one facet in the overall treatment plan for injured running athletes. Most overuse syndromes will respond to rest, training modification, and a change in the running surface or shoe. Equally important is the use of a proper conditioning and stretching programme both for injury prevention and for treatment of specific injuries. Treatment with orthotic shoe inserts should not be used as a substitute for any of these approaches.

ISSN:0112-1642    

DOI:10.2165/00007256-199315010-00006

出版商:Springer International Publishing    

年代:2012

数据来源: ADIS