McMaster University researchers have discovered that a key gene may explain why some people are energetic and others find it hard to get moving.

The team was working with mice, some of which had two genes removed. The genes control the AMP-activated protein kinase (or AMPK), an enzyme that is released during exercise.

While mice like to run, the mice without the genes were not as active as mice with the genes.

"While the normal mice could run for miles, those without the genes in their muscle could only run the same distance as down the hall and back," Gregory Steinberg, associate professor of medicine in the Michael G. DeGroote School of Medicine and Canada Research Chair in Metabolism and Obesity, said in a release Monday.

"The mice looked identical to their brothers or sisters, but within seconds we knew which ones had the genes and which one didn't."

The researchers found the mice without the AMPK genes had lower levels of mitochondria — sometimes described as cellular power plants — and their muscles were less able to take up glucose while they exercised.

By removing the genes, the researchers found that AMPK is the key regulator of the mitochondria, said Steinberg.

The research is in the current issue of the Proceedings of the National Academy of Sciences.

Research on mice is not always applicable to people.