Fitness Trackers May Fail Obese Individuals
Fitness trackers have become one of the most popular tools for measuring how many calories you’ve burned in a day. But for individuals dealing with obesity, who are known to have differences in energy burned, speed, and walking gait, these trackers are often inaccurate in monitoring activity- until now.
Fitness trackers may be underestimating calorie burn in obese individuals, which may lead to discouragement. A new smartwatch algorithm designed for individuals with obesity achieves over 95% accuracy in tracking calories burned.
Researchers at Northwestern University have designed a new algorithm that helps smartwatches to more precisely measure the calories burned by individuals with obesity throughout various physical exercises.
Nabil Alshurafa, whose Northwestern lab, HABits Lab, designed and tested the open-source, dominant-wrist algorithm, specially created for individuals with obesity. He noted that it’s been rigorously tested and is available for other scientists to utilize. The next move is to release an activity-monitoring app later this year. It will be available for both Android and IOS use.
"People with obesity could gain major health insights from activity trackers, but most current devices miss the mark," said Alshurafa, associate professor of behavioral medicine at Northwestern University Feinberg School of Medicine.
Activity-monitoring algorithms currently used in fitness trackers weren’t built for people with obesity. Hip-worn trackers frequently misread energy expenditure due to gait changes. Devices tilt in individuals with higher body weight, Alshurafa noted. Wrist-worn models offer more comfort, compliance, and accuracy across body types, but haven’t been scientifically evaluated or calibrated for obese subjects.
Alshurafa tested his lab’s algorithm against 11 state-of-the-art algorithms created by researchers utilizing research-grade trackers. He used wearable cameras to capture each moment when wrist sensors failed to catch calories burned. "Without a validated algorithm for wrist devices, we're still in the dark about exactly how much activity and energy people with obesity really get each day -- slowing our ability to tailor interventions and improve health outcomes”.
The findings were published on June 19 in Nature Scientific Reports.
Research motivated by an exercise class
The rationale for a new algorithm started after Alshurafa went to an exercise class with his mother-in-law, who has obesity.
"She worked harder than anyone else, yet when we glanced at the leaderboard, her numbers barely registered," Alshurafa said. "That moment hit me: fitness shouldn't feel like a trap for the people who need it most."
Algorithm challenges gold-standard methods
Through the use of commercial activity trackers, the new model challenges gold-standard methods of measuring energy burn and can monitor how much energy a person with obesity is using every minute with over 95% accuracy in real-world conditions. The technology makes it simpler for people with obesity to monitor their daily activities and energy usage, Alshurafa stated.
How the study measured calories used
Alshurafa’s research included 27 study subjects in one group who wore a fitness tracker and metabolic cart- a mask that tracks the volume of oxygen the user inhales and the volume of carbon dioxide the user exhales to measure their calorie burn (in kilocalories) and resting metabolic rate. The study subjects participated in a set of physical activities to track their calorie burn during each task. The researchers then evaluated the fitness tracker results to check how they compared to the results of the metabolic cart.
A second group of 25 study subjects wore a fitness tracker and body camera while going about their lives. The scientists could visually confirm when the algorithm was above or below the estimated calorie level using the body camera.
Alshurafa would push study subjects to do as many pushups as they could in five minutes.
"Many couldn't drop to the floor, but each one crushed wall-pushups, their arms shaking with effort," he said, "We celebrate 'standard' workouts as the ultimate test, but those standards leave out so many people. These experiences showed me we must rethink how gyms, trackers, and exercise programs measure success -- so no one's hard work goes unseen."
Below are tips to motivate clients to exercise:
· Check with your healthcare provider if you’re starting or haven’t exercised in a long time.
· Start slowly with just a few days per week and gradually build up your tolerance.
· Add exercise to your calendar to keep it consistent.
· Join a gym or class to keep yourself motivated.
· Have a friend, family member, or coworker join your exercise venture.
· Wear an exercise tracker, but keep in mind it may not be measuring your output. You are likely using more energy than you think!
· Mix up your exercise to challenge yourself. Do a combination of both cardio and weight-training exercises as tolerated.
· Consider water classes, which are often easier to participate in for those with arthritis.
· Hire a personal trainer to provide exercise tips and goal setting.
· Don’t give up. Try various forms of exercise to see what you enjoy most.
Lisa Andrews, MEd, RD, LD
Reference:
Wei, B., Romano, C., Pedram, M. et al. Developing and comparing a new BMI inclusive energy expenditure algorithm on wrist-worn wearables. Sci Rep 15, 20060 (2025). https://doi.org/10.1038/s41598-025-99963-0
