Pendergast D R, Horvath P J, Leddy J J, Venkatraman J T
Department of Physiology, State University of New York, Buffalo 14214-3078, USA.
Am J Sports Med. 1996;24(6 Suppl):S53-8.
This paper presents a model to evaluate the nutritional status of trained athletes based on work in our laboratory as well as others. The model proposes that substrate use is set by the muscle fibers recruited, based on the exercise intensity. Second, the substrate available is primarily determined by the intramuscular stores. In trained athletes, intramuscular fat plays an important role in metabolism at exercise intensities as high as 80% of maximal aerobic power. Based on these factors, increasing the fat in the diet (while maintaining adequate intramuscular glycogen) increases VO2max and intramuscular stores of fat (presumably due to increased mitochondrial volume). These two factors result in a significant increase in the time to exhaustion at set levels of exercise (endurance). It also appears that fatigue is associated with depletion of either glycogen or fat. These conclusions hold true for athletes on diets where sufficient calories are taken in to meet demands and for exercise levels below 80% of VO2max, where primarily slow-twitch oxidative fibers are used. These data may not apply in exercise where predominantly fast-twitch fibers are used. Also, these data do not apply to runners eating a hypocaloric diet, where reducing the percentage of carbohydrates may compromise their glycogen stores. It would appear that the fat in the diet can be increased to a very high level without compromising the cardiovascular or immune systems of athletes. Moreover, it can be proposed that these data could be applied to sedentary persons, as long as they are isocaloric. This would imply that the fat consumed in the diet would be used in the muscle, as in the runners, although at a lower level. Thus, the dietary intake should be matched in both total calories and percentage of fats and carbohydrates to calories consumed by daily activity. It should be cautioned that if glycogen and fat stores are compromised, protein resynthesis is inhibited and loss of muscle mass may result. This has a negative effect on the athlete's ability to perform at high levels.
本文基于我们实验室以及其他机构的研究成果，提出了一个评估训练有素的运动员营养状况的模型。该模型认为，根据运动强度，所募集的肌纤维决定了底物的利用情况。其次，可用底物主要由肌肉内储备决定。在训练有素的运动员中，肌肉内脂肪在高达最大有氧功率80%的运动强度下的新陈代谢中起着重要作用。基于这些因素，增加饮食中的脂肪（同时保持充足的肌肉内糖原）可提高最大摄氧量和肌肉内脂肪储备（可能是由于线粒体体积增加）。这两个因素导致在设定的运动水平（耐力）下疲劳时间显著延长。此外，疲劳似乎与糖原或脂肪的耗尽有关。这些结论适用于摄入足够热量以满足需求的运动员饮食，以及低于最大摄氧量80%的运动水平，此时主要使用慢肌纤维。这些数据可能不适用于主要使用快肌纤维的运动。此外，这些数据不适用于摄入低热量饮食的跑步者，减少碳水化合物的比例可能会损害他们的糖原储备。似乎饮食中的脂肪可以增加到很高水平而不会损害运动员的心血管或免疫系统。此外，可以提出这些数据可应用于久坐不动的人，只要他们摄入的热量相同。这意味着饮食中消耗的脂肪将像跑步者一样在肌肉中被利用，尽管水平较低。因此，饮食摄入量应在总热量以及脂肪和碳水化合物的百分比方面与日常活动消耗的热量相匹配。需要注意的是，如果糖原和脂肪储备受损，蛋白质再合成会受到抑制，可能导致肌肉量流失。这会对运动员高水平表现的能力产生负面影响。
