Brooks G A
Department of Physical Education, University of California, Berkeley 94720.
Med Sci Sports Exerc. 1987 Oct;19(5 Suppl):S150-6.
The integrated use of several energy sources allows high muscular power outputs to be sustained. Muscle glycogen provides the major fuel source for muscular exercise, but other fuels can provide alternative energy sources which allow for muscle glycogen-sparing and an increased potential for prolonged high metabolic rates. Blood-borne glucose, derived from liver glycogenolysis and glyconeogenesis, as well as intra-muscular lipids and plasma free fatty acids derived from adipose tissue provide the main energy alternatives to muscle glycogen. Several amino acids, including the essential amino acid leucine, are also used directly as oxidizable fuels during exercise. Depending on the duration and intensity of exercise and other factors such as glycogen stores and energy intake, amino acids can provide from a few to approximately 10% of the total energy for sustained exercise. Additionally, many amino acids can be converted to glutamate (via glutamate dehydrogenase) and then to alanine (via glutamate-pyruvate transaminase). Alanine, along with lactate and pyruvate, are recognized as the major gluconeogenic precursors. Via this mechanism, several amino acids play crucial roles in providing the carbon sources for maintaining blood glucose homeostasis during exercise and glycogen restitution during recovery. And finally, during exercise and recovery, amino acids likely play important anaplerotic functions sustaining the whole metabolic apparatus.
多种能源的综合利用可使高肌肉功率输出得以维持。肌肉糖原是肌肉运动的主要燃料来源，但其他燃料可提供替代能源，从而节省肌肉糖原，并增加长时间维持高代谢率的潜力。来自肝糖原分解和糖异生的血糖，以及来自肌肉内脂质和脂肪组织的血浆游离脂肪酸，是肌肉糖原的主要替代能源。包括必需氨基酸亮氨酸在内的几种氨基酸在运动过程中也直接用作可氧化燃料。根据运动的持续时间和强度以及其他因素（如糖原储备和能量摄入），氨基酸可为持续运动提供总能量的几%至约10%。此外，许多氨基酸可转化为谷氨酸（通过谷氨酸脱氢酶），然后转化为丙氨酸（通过谷丙转氨酶）。丙氨酸与乳酸和丙酮酸一起，被认为是主要的糖异生前体。通过这种机制，几种氨基酸在运动期间为维持血糖稳态提供碳源以及在恢复期间糖原恢复方面发挥关键作用。最后，在运动和恢复过程中，氨基酸可能在维持整个代谢装置方面发挥重要的回补功能。
