Stamina was the ability to continue performing physical or mental tasks without tiring.

In 2348, Julian Bashir, a Human from Earth, illegally received a form of DNA resequencing on Adigeon Prime known technically as accelerated critical neural pathway formation. These "treatments" accelerated the growth of neuronal networks in his cerebral cortex, enhancing his mental abilities and allowing his intelligence quotient to jump five points a day for over two weeks. Further "treatments" led to improvements in his hand-eye coordination, reflexes, vision, stamina, height, and weight. (DS9: "Doctor Bashir, I Presume")

Some geneticists were of the opinion that Klingons developed a third lung in order to increase their stamina while fighting. (VOY: "Lineage")