I’m going to spend my lunch hour at the gym today. I have to, after the message I heard last night.I went over to Northwestern University’s Chicago campus last night to attend the second event of the year sponsored by the Chicago Council on Science and Technology. The speaker was Toby Tate, Ph.D., dean of the College of Applied Health Sciences at the University of Illinois at Chicago.

Tate’s message was simple and direct: Only 5% of the people in the United States exercise at an intensity and duration that result in health benefits. And the reason? “Because we don’t have to,” she said.

She’s right. We all have to eat every day, but unlike our ancestors, like Cro Magnon man, we don’t have to go foraging and hunting for food. We drive to the store. When we get home, we have electric gadgets to open the cans.

Likewise, when we go to work, we don’t have to walk or ride a bike. We have cars and mass transit that take us from door to door. And when we get to work, escalators and elevators take us up and down the stairs.

“Convenience is killing us,” Tate said, because it is taking away the challenges that used to force us into physical activity. The resulting sedentary lifestyle has been linked to many diseases and chronic medical conditions, and it contributes to obesity.

Interestingly, Tate said regular exercise doesn’t really extend the lifespan. What it does do is extend the “healthspan.” In other words, people who get regular exercise will have a shorter “zone of disability” than those who don’t. Tate said the average zone of disability in the United States is 10%. That means most people will spend 10% of their lives disabled.

It’s all about independence, Tate said: “To be able to get out of a chair. By yourself. To be able to open a jar of peanut butter. By yourself.”

Her advice? “Find your inner athlete,” she said. Find a type of exercise that you really like. And then do it.