Johnson J M
Department of Physiology, University of Texas Health Science Center at San Antonio, 78284-7756, USA.
Med Sci Sports Exerc. 1998 Mar;30(3):382-6. doi: 10.1097/00005768-199803000-00007.
The process of physical training places frequent significant demands for increased blood flow to cardiac and skeletal muscle tissues and sets into action adaptive responses to better enable the circulatory system to meet those demands. These adaptive changes and the associated mechanisms are dealt with elegantly in other portions of this symposium. The repeated bouts of dynamic exercise with training also expose the temperature regulatory system to increased body temperatures and attendant demands for increased heat loss. These frequent demands for increased heat loss lead to adaptations in the control of the cutaneous circulation. There are consistent results among the limited number of studies conducted to test this question directly. The primary result is that skin blood flow in the trained state is higher at a given level of internal temperature than in the sedentary or less trained state. This result is seen in both cross-sectional and longitudinal comparisons, in older and younger subjects, in responses to heat at rest and during exercise, and in the changes with detraining as well as those attending training. In some studies this adjustment is made by a shift in the threshold internal temperature at which skin blood flow begins to rise, whereas in others it is accomplished by an increase in the sensitivity of the skin blood flow-internal temperature relationship. Reasons for this variation are not clear. The cutaneous circulation is controlled by vasoconstrictor and separate vasodilator nerves, but it is not clear how much of the training effect is manifest through one or the other neural system. However, indirect data suggest that vasoconstrictor activity is generally reduced and that active vasodilator activity is initiated at lower internal temperatures. It is also not clear to what extent the mechanism for the training effect is through the acclimatization process, as opposed to the influence of training, itself. In any case, the adjustments in control of the cutaneous circulation with physical training increase the capacity of the circulation to transport and eliminate heat as that training process increases the capacity of the active tissues to produce that heat.
体育训练过程经常对增加流向心脏和骨骼肌组织的血流量提出显著要求，并引发适应性反应，以使循环系统更好地满足这些需求。本次研讨会的其他部分已对这些适应性变化及其相关机制进行了精彩阐述。训练中反复进行的动态运动还会使体温调节系统面临体温升高以及随之而来的增加散热的需求。这些对增加散热的频繁需求导致皮肤循环控制出现适应性变化。在直接测试该问题的有限数量研究中，结果是一致的。主要结果是，在给定的内部温度水平下，训练状态下的皮肤血流量高于久坐或训练较少状态下的皮肤血流量。在横断面和纵向比较中、在老年和年轻受试者中、在静息和运动时对热的反应中、在停训后的变化以及训练过程中的变化中，均可见到这一结果。在一些研究中，这种调整是通过皮肤血流量开始增加时的阈值内部温度的变化来实现的，而在另一些研究中，则是通过皮肤血流量与内部温度关系的敏感性增加来实现的。这种差异的原因尚不清楚。皮肤循环由血管收缩神经和独立的血管舒张神经控制，但尚不清楚训练效果在多大程度上通过其中一个或另一个神经系统体现出来。然而，间接数据表明，血管收缩活动通常会减少，而活跃的血管舒张活动会在较低的内部温度下启动。同样不清楚训练效果的机制在多大程度上是通过适应过程，而非训练本身的影响。无论如何，体育训练对皮肤循环控制的调整增加了循环系统运输和散发热量的能力，因为该训练过程增加了活跃组织产生热量的能力。
