Brouns F, Beckers E, Wagenmakers A J, Saris W H
Department of Human Biology, University of Limburg, Maastricht, Netherlands.
Int J Sports Med. 1990 May;11 Suppl 2:S78-84. doi: 10.1055/s-2007-1024858.
In a number of individual cycling tests lasting 2.5-5 h with alternating exercise intensities of 50%-85% of maximal working capacity, it was observed that plasma ammonia levels may rise above 250 mumol/l when reaching exhaustion, while lactate levels remain relatively low. Acute quantitative ammonia production during intensive endurance exercise may be enhanced by a reduced glycogen availability in muscle. However, adequate amounts of glycogen itself do not prevent ammonia production when exercise is at high intensity and long-lasting. The continuous ammonia accumulation in blood during endurance exercise in trained individuals may be the result of a relatively low blood flow to the liver and thereby low clearance in contrast to lactate which may not accumulate due to a high clearance rate in both active and nonactive oxidative muscle fibers. In a number of subjects it was observed that exhaustion, when performing endurance exercise at high exercise intensities, occurred when plasma ammonia levels were high. Muscle cramps occurred in subjects who reached their highest individual ammonia values and seemed not to be related to serum potassium, plasma lactate, or muscle glycogen. These individual observations give rise to the hypothesis that high intramuscular ammonia levels may be related to the etiology of muscle exhaustion and muscle cramping during highly intensive endurance exercise.
在一系列时长为2.5至5小时、运动强度在最大工作能力的50%至85%之间交替的个体骑行测试中，观察到当达到疲劳状态时，血浆氨水平可能会升至250微摩尔/升以上，而乳酸水平则相对较低。高强度耐力运动期间急性氨的定量产生可能会因肌肉中糖原可用性降低而增强。然而，当运动强度高且持续时间长时，足够量的糖原本身并不能阻止氨的产生。与乳酸不同，由于活跃和非活跃氧化肌纤维中乳酸清除率高，乳酸不会积累，而训练有素的个体在耐力运动期间血液中氨的持续积累可能是由于肝脏血流相对较低，从而清除率较低所致。在一些受试者中观察到，在进行高强度耐力运动时，当血浆氨水平较高时会出现疲劳。肌肉痉挛发生在达到其个体最高氨值的受试者中，似乎与血清钾、血浆乳酸或肌肉糖原无关。这些个体观察结果提出了一个假设，即高肌肉氨水平可能与高强度耐力运动期间肌肉疲劳和肌肉痉挛的病因有关。
