Final answer:
The post-training period when a trained function demonstrates a higher performance capacity than before training, according to the gas principle, is called the supercompensation phase. This phase involves physiological adaptations that improve endurance and reduce fatigue.
Step-by-step explanation:
As it relates to the gas principle, the post-training period when the trained function has a higher performance capacity than prior to the training period is known as the supercompensation phase. During this phase, the body undergoes physiological adaptations, such as the formation of more extensive capillary networks (angiogenesis) around muscle fibers and an increase in the efficiency of oxygen and waste product exchange. These changes result from the body's response to the stress applied during training and lead to an enhanced ability to perform the trained activity with improved endurance and reduced fatigue.