Fitness: How much are you really exercising?

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Most recommendations on the amount of exercise that is needed to improve health are based on self-reported data. Study subjects are quizzed on how often they engage in physical activity, what types of activity they do and how long they typically exercise. Yet most respondents struggle to accurately report their movement patterns, especially when asked to reach back several days or weeks.

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It’s not just poor recall that makes self-reporting such a challenge. There’s a strong tendency to be generous when recounting exercise frequency and duration. The same goes for intensity; due to its subjective nature, it’s even more challenging to interpret whether a workout was easy, moderate or hard.

These flaws in data collection have been acknowledged by most researchers, but up until the last few years there were few other options. Sophisticated activity trackers are expensive, limiting the ability to use them on a large pool of study subjects. But with the proliferation of consumer-based wearables that collect data 24/7, a more accurate picture of exercise habits is starting to appear.

But accurately tracking physical activity isn’t the only challenge when it comes to determining the role exercise plays in boosting health and wellness. Time spent being sedentary is subject to the same fallacies in self-reporting. People routinely underestimate the number of hours they spend in front of a screen or in a chair. And since the amount of active versus sedentary pursuits is considered a valuable predictor of health and longevity, more accurate data would provide a detailed and scientifically validated set of guidelines regarding how hard and how often we need to exercise in order to combat the consequences of inactivity.

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With that goal in mind, a team from the Mackenzie Wearables Research Hub at the University of Sydney in Australia examined data from a whopping 73,729 study subjects wearing fitness trackers to get a true picture of the impact exercise and sedentary time have on long-term health.

“We examined the joint associations of sedentary time and intensity-specific physical activity with all-cause and cardiovascular disease mortality,” said the researchers.

Wearing an accelerometer for one week, the subjects offered insight into their daily habits, including the volume and intensity of physical activity and the amount of time spent being sedentary. Daily activity was classified into four categories: sedentary, standing chores of everyday life (washing dishes, cooking), walking activities (gardening, house cleaning, commuting) and high-energy physical activity (purposeful exercise and vigorous movement). There were also four categories of intensity: sedentary, light, moderate and vigorous. Data was categorized based on volume and intensity of activity and analyzed against records of deaths occurring during a six-year followup period.

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Some of the results echoed similar studies, including confirmation that the most sedentary subjects were more likely to die within the followup period. Also endorsed was the theory that physical activity of any intensity reduces mortality risk. But the study adds more clarity on how long and how hard we need to exercise to improve longevity.

“Specifically, we showed that a median of six minutes per day of vigorous physical activity, 30 minutes a day of moderate to vigorous activity, 64 minutes a day of moderate or 163 minutes of light physical activity may attenuate the association between high sedentary time (more than 11 hours a day) and mortality,” said the researchers.

How does this information change what we already know about the impact of exercise on long-term health? More than just stating the need to accumulate 150 minutes of moderate-intensity exercise per week, the research team provides a set of guidelines based on intensity. So instead of setting the same bar for runners, walkers and plodders, individuals can set a baseline target of weekly exercise minutes according to the intensity of their workout. Runners need six minutes of exercise a day to lessen their risk of chronic disease, brisk walkers need 64 minutes and plodders need 163 minutes to ward off the unhealthy consequences of too many hours spent sitting behind a desk or looking at a screen.

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Keep in mind that these numbers represent the minimum amount of exercise needed to reduce the risk of chronic disease. The longer the workout and the more vigorous the intensity, the greater the benefits, and not just to health. Building muscle, improving aerobic endurance and optimizing joint range of motion are building blocks for improved athletic performance and overall fitness. Fit individuals maintain their quality of life longer than those who meet exercise minimums.

Adding more exercise minutes to your week, some of which are at an intensity that pushes your limits, and reducing the time spent being inactive remains the goal of anyone who wants to maintain their health and vigour as they age. And just to be sure you’re not overestimating how much and how hard you exercise, consider using an activity tracker (such as an Apple Watch, Fitbit or Garmin) to keep yourself honest.

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