Martin W H
Division of Cardiology 111A/JC, John Cochran Hospital, St Louis, Missouri, USA.
Exerc Sport Sci Rev. 1996;24:203-31.
Fatty acids are an important source of energy for skeletal muscle contraction, particularly during exercise of mild-moderate intensity, prolonged duration, and in the fasting state. Plasma FFA transported from remote adipose tissue stores and triglycerides contained within skeletal muscle fibers are the major sources of these fatty acids. The relative contribution of each source is dependent on the mode, intensity, and duration of exercise and on training status. Plasma FFA oxidation is directly related to the rate of lipolysis in adiopose tissue. The most potent stimulants of the latter are the catecholamines, but a lower plasma insulin concentration during exercise also plays a contributory role. In contrast, intramuscular triglyceride hydrolysis appears to be mediated entirely by beta 2-adrenergic stimulation. Endurance training substantially enhances fatty acid oxidative capacity in skeletal muscle and increases the proportion of energy derived from fatty acid oxidation during exercise. In addition, the sympathoadrenal response to exercise is markedly blunted in the trained state. Studies conducted in our laboratory indicate that plasma FFA and glycerol concentrations and whole body FFA uptake and oxidation are all decreased during moderate-intensity exercise at the same absolute work rate after physical conditioning, probably because of the reduction of sympathoadrenal activity. However, the lipolytic response to catecholamines also is enhanced in trained subjects. Perhaps as a consequence, the magnitude of the decrease in lipolysis and plasma FFA oxidation is less than the decrement in sympathoadrenal activity in the same individuals during exercise in the trained state. Other investigations were conducted in our laboratory to determine the source of the additional fatty acids oxidized in physically conditioned subjects. These studies demonstrated that during moderate-intensity exercise at the same absolute work rate, depletion of triglycerides from within skeletal muscle fibers was twice as great after, as opposed to, before training. Regardless of training status, intramuscular triglyceride use accounted for about 90% of the oxidized fatty acids that were not supplied from adipose tissue via the plasma. Intramuscular triglycerides were the source of virtually all of the additional fatty acids oxidized in the trained state. Both before and after physical conditioning they explained the discrepancy between the rates of plasma FFA and total fat oxidation during moderate-intensity exercise of up to 2 hr in duration.
脂肪酸是骨骼肌收缩的重要能量来源，尤其是在中低强度、长时间运动以及禁食状态下。从远处脂肪组织储存转运而来的血浆游离脂肪酸（FFA）以及骨骼肌纤维内所含的甘油三酯是这些脂肪酸的主要来源。每种来源的相对贡献取决于运动的方式、强度和持续时间以及训练状态。血浆FFA氧化与脂肪组织中的脂解速率直接相关。后者最有效的刺激物是儿茶酚胺，但运动期间较低的血浆胰岛素浓度也起一定作用。相比之下，肌内甘油三酯水解似乎完全由β2 - 肾上腺素能刺激介导。耐力训练可显著增强骨骼肌的脂肪酸氧化能力，并增加运动期间脂肪酸氧化所提供能量的比例。此外，训练状态下交感肾上腺对运动的反应明显减弱。我们实验室进行的研究表明，在体能训练后，以相同的绝对工作速率进行中等强度运动时，血浆FFA和甘油浓度以及全身FFA摄取和氧化均降低，这可能是由于交感肾上腺活动的降低。然而，训练有素的受试者对儿茶酚胺的脂解反应也增强。也许因此，在训练状态下运动时，相同个体的脂解和血浆FFA氧化减少的幅度小于交感肾上腺活动的减少幅度。我们实验室还进行了其他研究，以确定体能训练有素的受试者中额外氧化的脂肪酸的来源。这些研究表明，在以相同的绝对工作速率进行中等强度运动时，训练后骨骼肌纤维内甘油三酯的消耗是训练前的两倍。无论训练状态如何，肌内甘油三酯的利用约占非通过血浆从脂肪组织供应的氧化脂肪酸的90%。肌内甘油三酯实际上是训练状态下所有额外氧化脂肪酸的来源。在体能训练前后，它们都解释了长达2小时的中等强度运动期间血浆FFA和总脂肪氧化速率之间的差异。
