Physical activity needs for health payoffs often underestimated

About 15 per cent of adults and fewer than 10 per cent of teens meet physical activity guidelines for health benefits, with some not really realizing what it takes to make gains, according to Statistics Canada.

New descriptions for moderate and vigorous activity may be needed, researchers say

Physical activity needs for health payoffs often underestimated

9 years ago
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Featured VideoA new study says many people who exercise think they are doing more than they actually are

About 15 per cent of adults and fewer than 10 per cent of teens meet physical activity guidelines for health benefits, with some not really realizing what it takes to make gains, according to Statistics Canada.

The agency compared self-reported physical activity during leisure time and objectively measured movements with a device called an accelerometer that is worn on the waist.

At the individual level, there was a discrepancy between how much some people thought they were moving and the measurements, both in terms of time spent and intensity. 

How much people think they're moving and what's objectively measured don't always match up. (Melanie Glanz/CBC)

"If you look at the measured data, we only have 10 per cent of teenagers that are meeting the guideline and 15 per cent of adults are meeting the guidelines, so there is room for improvement for sure," said Didier Garriguet of Statistics Canada's health analysis division in Ottawa.

Using self-reported data from a questionnaire, closer to between 30 and 50 per cent of people will meet the guidelines, Garriguet said.

"Maybe they're exaggerating like overestimating what they're doing," he said in an interview.

The difference in terms of minutes were pretty close for teenagers. But for older adults, there was about 16 minutes less of physical activity with the measured data on average compared with self-reported data, he said.

Garriguet pointed to a few possibilities to explain the discrepancy:

  • A matter of perception of the time you're doing an activity versus the time actually spent moving.
  • A difference in terms of intensity, such as walking at a pace that isn't fast enough to register, particularly for the older population.

The differences arise since the devices and questionnaires measure different aspects of physical activity. For instance, someone could report that they played hockey for one hour but the accelerometer only records 20 minutes.

York study: Some exercisers overestimate intensity

The findings come on the heels of a study published in May by researchers at York University in Toronto.

They found adults underestimate what the national guidelines for moderate to vigorous intensity physical activity are and overestimate how much they do.

Canadian physical activity guidelines, published in 2011, recommend those aged 12 to 17 get 60 minutes of moderate to vigorous intensity physical activity daily. For adults, the guidelines recommend that adults obtain 150 minutes of
physical activity of that intensity per week, accumulated in bouts of 10 or more minutes.

In the York study, 129 participants aged 18 to 64 walked or jogged on a treadmill at a speed that they felt corresponded to light, moderate and vigorous intensity. Researchers asked them to judge the intensity based on how warm and out of breath they felt.

Most of the study participants were young, normal-weight women with poor cardiovascular fitness, the researchers said. More than half, 57 per cent, said they met the minimum guidelines for moderate intensity physical activity.

But they underestimated how hard they should be working to achieve moderate and vigorous intensity, the researchers found.

"In conclusion, this is the first study to determine that adults of different sexes, ethnicities and body mass index classifications underestimate moderate and vigorous intensity physical activity, and underestimate the physical activity intensity recommended for health," Prof. Jennifer Kuk of the School of Kinesiology and Health Science at York and her co-authors said.

The guidelines say that for adults to achieve a moderate intensity, their heart rates should be within the range of 64 to 76 per cent of their maximum heart rate and between 77 to 83 per cent for vigorous intensity.

"With a lot of health promotion campaigns nowadays, they like to say exercise is easy, everybody can do it. So that may have changed how people perceive moderate and vigorous intensity exercise," said Ruth Brown, a co-author of the York paper.

The York team suggested new, subjective descriptions for moderate and vigorous intensity may be needed to help people to correctly interpret the guidelines.

Brown's tips include:

  • Use the heart rate rule of thumb of 220 minus your age to get the maximum.
  • Pay attention to your breathing rate. You should be starting to feel more out of breath.
  • You should be sweating and getting warmer.
  • Try the talk test — you should be having more difficulty talking or holding a conversation.

Brown raised another potential issue. Sometimes she sees people working out at the gym doing the same exercise on the same machine at the same level each time without taking into account that they're getting fitter and need to increase the intensity to get fitter.

The York researchers acknowledged limitations of the study, such as how the results need to be verified in older populations.

In the Statistics Canada report, self-reported walking and gardening accounted for much of the discrepancy between self reports and measurements for the older group.

The Statistics Canada questionnaire didn't ask about active transport, such as walking or cycling to school or work, or physical activity on the job or at school. It was based on a total of 7,158 participants from the 2007 to 2009 and 2009 to 2011 Canadian Health Measures Survey,

The findings were published in Wednesday's issue of the agency's Health Reports.

With files from CBC's Melanie Glanz and Pauline Dakin