Exercise physiologists tested the iWatch and found that accuracy was dependent on intensity level.
Fitness trackers are becoming more and more popular as everyone is interested in counting how many steps they took daily and how many calories they burned. But do they work just as well for people who use wheelchairs for mobility?
This is the question that researchers at the School of Exercise and Dietetics at San Diego State University set out to answer by comparing the devices to laboratory equipment designed to measure accurate caloric expenditure.
Exercise physiologist and associate professor Jochen Kresler and graduate student Daniel Moreno studied 15 non-disabled people and 15 wheelchair users who performed similar exercises on wheelchair treadmills called roller systems.
“Adaptive fitness is a workout for people with special needs, and they are just like everyone else, interested in knowing how many calories they burn,” said Kresler. “In the lab, we measure breathing gas intake to give accurate calorie counts with a portable metabolic cart, but fitness trackers are much easier to use, so we wanted to see if they provide an accurate measurement.”
He and Moreno found that at higher intensity levels - increased wheelchair impacts - the iWatch’s metabolic response measurements were more accurate, but at lower intensity levels the measurements were turned off.
Takeaway: Trackers are not well suited for wheelchair treadmills or hand cycles.
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The self-funded study was published in the International Journal of Sports Medicine in March.
Chairler noted that trackers count “steps” even if the user simply shakes one of them with his hand. “So the trackers don’t count actual steps or bumps, but actually measure acceleration in all three planes - up and down, back and forth, and side to side.”
Metabolic Response - which is the Chair’s area of expertise - measures oxygen consumption and carbon dioxide emissions during breathing, which is then used to calculate caloric expenditure. It can help people decide how to change what they eat and how they exercise. Along with the iWatch, the participants in the trial wore a mask connected to a gas analyzer attached to their chest, connected wirelessly to a computer that analyzes the measurements.
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Kresler and Moreno observed the two groups and found that there was no significant difference in how the smartwatch measured calories burned. for sets of 30, 45 and 60 stroke counts, so the results were pooled for both groups.
The tracker underestimated the calories burned on the treadmill but overestimated the calories burned on the arm cycle by an average of two to five kilocalories (kcal) in three minutes. Extrapolated to an hour of activity, which translates to a tracker underestimating about 40 to 100 calories per hour for a treadmill and about 20 to 60 calories for an arm cycle.
It all comes down to how important these measurements are to each user.
“I would not use it in a laboratory, but everyone has to decide for themselves,” said Kresler.
However, to get accurate measurements with the equipment he used, currently the only option is to go to health spas or physical physiology laboratories. Moving forward, he plans for people to wear the next generation iWatch and go about their normal day so that he can observe them in the field rather than in the laboratory.