Fitness Trackers Offer Widely Different Data, Experiment Finds

An experiment involving five different fitness trackers simultaneously revealed considerable variations in the data collected, particularly concerning sleep stages and calorie expenditure. The findings suggest that users may be basing their health decisions on inconsistent information.

The test, conducted over four days, involved a Garmin watch, a Whoop band, an Oura Ring, an iPhone with Apple Health, and the Eight Sleep mattress, which also tracks sleep. The participant noted the discomfort and constant notifications from the devices, which included prompts to move or warnings about stress levels. One evening, the Oura Ring advised winding down for sleep at 8:15 p.m. while the participant was engaged in household chores.

Discrepancies were particularly notable in sleep tracking, with differences of up to an hour in recorded 'deep sleep' and a 40-minute variation in total sleep duration between devices on a single night. For example, the Eight Sleep recorded 6 hours and 57 minutes of sleep, while the Oura Ring logged 6 hours and 17 minutes.

Calorie tracking also showed significant variance. On one day, the Oura Ring estimated 2,580 calories burned, while the Whoop band estimated only 1,436, a difference of over 1,100 calories. Such disparities could significantly impact individuals attempting to manage weight based on these metrics.

Step count data proved to be the least variable, with devices generally falling within a 1,000 to 2,000 step range of each other daily. Even the Apple Health app, which relies on the iPhone's sensors, provided comparable step counts, despite not being constantly monitored for every step.

Michael Sawh, a journalist specializing in wearable technology, explained that while many trackers use similar sensors, the proprietary algorithms used to interpret the data differ. This can lead to the inconsistencies observed in the experiment.

Beyond the technical variability, the psychological impact of fitness trackers was also examined. Research fellow Paulina Bondaronek of University College London noted that users of fitness and calorie-counting apps often experience shame, guilt, stress, and demotivation when failing to meet targets. Some apps, with their 'all-or-nothing' approach to streaks, can exacerbate these negative feelings.

Bondaronek also highlighted the importance of self-belief and identity in maintaining healthy behaviors. Simply tracking an activity, like walking 10,000 steps, does not automatically lead to adopting an active identity. Individuals who see themselves as 'runners,' for instance, are more likely to maintain their running habits than those who simply 'try to run more,' as the former integrates the behavior into their self-identity.

The participant in the experiment concluded that while they view their fitness trackers as useful tools that align with their established identity as an active person, others might find negative data points feel like a personal indictment rather than objective information. Despite notifications urging continuous wear for optimal feedback, the participant chose to stop using the devices, asserting control over their relationship with the technology.