Our happy hour fact to amaze your drinking buddies with.

Up to one in five people have an "unfitness" gene, which severely limits their ability to increase their aerobic capacity.

After having 600 volunteers take up a cycling training program, researchers tracked improvements in their fitness, including how much oxygen they could inhale (an indicator of a healthy heart). About 20 percent of the volunteers, who shared a similar cluster of genes, were unable to get any cardiovascular benefit from the exercise.

"The change in aerobic fitness was so small, you could miss it," said one of the researchers. On the other hand, 10 percent of the volunteers, who also shared another genetic cluster, saw "massive improvements" when compared to the rest of the group.

Soon there will be a simple blood test to determine if you have the "unfitness gene." We recommend everyone play it safe (and not risk wasting their time) by taking it easy until then. (Or just take this.)