Over the last few years, researchers in Canada have been working on an experiment to see if people actually know how hard exercise really is. They put a bunch of participants on a treadmill and asked them to set it to a speed constituting a rigorous workout. According to the results of the study, published in PLoS One last month, more than half of them thought they were working hard, but in fact, experts considered their speeds "light."

This matters. In 2008, 57 million humans died. According to a 2012 paper, 5.3 million of those deaths (about nine percent) were because of "inactivity." The authors estimated that "elimination of physical inactivity would increase the life expectancy of the world's population" by at least a few months or even up to a year.

The authors of the present study, a team of York University scientists in Toronto, wanted to find out whether people even knew what exercise means. According to their paper, public health experts have various, but similar, standards for what constitutes light, moderate and vigorous workout intensity. The government in Canada circulates a guidebook called Canada's Physical Activity Guidelines, which recommends minimum heart rates necessary to gather health benefits.

So, how well do Canadians know the guides? Not well. The 129 participants, most of them women, were between 18 and 64 and were instructed to read the guidelines. To be sure they understood the differences between light, moderate, and vigorous exercise, they were tested on what they read. Then the scientists plopped them onto a treadmill.

The investigator read the following descriptor definitions to the participants. For light effort: "You are starting to feel warm and you have a slight increase in breathing rate"; for moderate effort: "You are warmer and you have a greater increase in breathing rate"; and for vigorous effort: "You are quite warm and more out of breath".

The results were discouraging. People who took a stroll thought they were training for a 5k. "When directed to walk at a pace that the participants thought would provide health benefits ... 52 percent walked at a light effort pace," according to the paper. Worse, only five percent walked at a vigorous pace. Lead author Jennifer Kuk told CTV News that the takeaway is that many people understimate how hard they need to work to achieve optimal health benefits from exercise. "This is worrisome both for personal and public health, and well-being," she said.

Source: Kuk J, Canning K, Brown R, et al. Individuals Underestimate Moderate and Vigorous Intensity Physical Activity. PLoS One. 2014.