Are Fitness Trackers and Running Watches Accurate? What The Latest Studies Reveal

Can we rely solely on our fitness tracker’s data? Or is there more to it?

Wearable devices, like Garmin, Apple Watch, Whoop Band, or Fitbit, have revolutionized the landscape of sports.

These gadgets, once seen as mere novelties or “random number generators” by many in the coaching industry due to their once questionable level of reliability and obscure algorithms, have now become essential in offering insights into performance, health, and overall well-being.

Wearables, especially fully featured GPS running watches, offer a great way of logging your workouts, training volume, and effort level without using a coach.

However, the reliability and accuracy of these devices’ data have always been scrutinized.

Close-up of an Apple Watch showing a fitness tracker with a question mark.
Credit: Marathon Handbook Staff

A recent study published in the International Journal of Sports Science and Coaching1Lundstrom, E. A., Jane, M., Koltun, K. J., Nicole C.A. Strock, Canil, H. N., & Williams, N. I. (2023). Wearable technology metrics are associated with energy deficiency and psychological stress in elite swimmers. International Journal of Sports Science & Coaching. https://doi.org/10.1177/17479541231206424provides further insight into this debate. The study focused on 27 collegiate-level swimmers during an intensified training period.

Researchers equipped these athletes with Whoop straps, a popular wearable technology, to collect various data.

In addition, the swimmers were asked to fill out the RESTQ, a subjective stress and recovery questionnaire, while also having their resting metabolic rate and T3 levels, a thyroid hormone linked with energy deficiency, measured.

The findings of this study are quite revealing, particularly in the context of how effective these wearables are in measuring strain and recovery.

Across the board, both male and female athletes showed no significant correlation between the Whoop strain and recovery index, physiological variables, or the RESTQ measures of stress and recovery.

Although there was some correlation, the lack of statistical significance suggests that the observed relationships could have arisen by random chance, and they do not provide substantial evidence to support the idea that fitness watch data can reliably predict levels of stress and recovery.

This lack of correlation was more pronounced when the group was divided by gender.

In males, only the Whoop strain score showed some correlation with resting metabolic rate and a few subjective stress scores. However, the recovery scores did not correlate with any measured variables.

In females, neither the recovery nor the strain score showed any significant correlation with the assessed parameters.

These findings raise crucial questions about the effectiveness of Whoop’s algorithms in accurately determining an athlete’s strain or recovery.

The low correlation between these wearable-derived metrics and physiological and subjective assessments of stress and recovery suggests that these devices might not be as reliable as once thought.

Are Fitness Trackers and Running Watches Accurate? What The Latest Studies Reveal 1

This recent study isn’t the first to call accuracy into question either in 2021, a study published in the “Journal of Sports Medicine and Physical Fitness”2JAGIM, A. R., KOCH-GALLUP, N., CAMIC, C. L., KROENING, L., NOLTE, C., SCHROEDER, C., GRAN, L., & ERICKSON, J. L. (2021). The accuracy of fitness watches for the measurement of heart rate and energy expenditure during moderate intensity exercise. The Journal of Sports Medicine and Physical Fitness61(2). https://doi.org/10.23736/s0022-4707.20.11151-4examined the accuracy of fitness watches by comparing the Fitbit Versa and Polar Ignite, along with a chest-worn heart rate monitor, Polar TeamPro Sensor, against standard medical equipment.

Twenty participants engaged in moderate-intensity exercise while wearing these devices.

Results showed that for heart rate (HR) measurements, the Fitbit and Polar Ignite had mean absolute percentage errors of 11.6% and 11.0%, respectively, while the chest-worn monitor had a lower error rate of 6.3%.

For runners, accurate HR monitoring is crucial for training within specific heart rate zones, which can affect the efficiency and outcome of their training.

The margin of error seen in the HR readings above could lead to runners training at an intensity level different from their target.

If a runner aims to maintain their heart rate in a specific zone, such as 150-160 beats per minute (bpm) for a moderate-intensity workout, the Fitbit mean absolute percentage error of 11.6% could vary this reading substantially.

This means a displayed heart rate of 155 bpm on the Fitbit could be off by about 18 bpm (11.6% of 155), placing the true heart rate somewhere between 137 and 173 bpm.

So, what’s the bottom line? Are fitness watches accurate?

The take-home message from this study is clear and straightforward: reliance solely on wearables like Whoop, Garmin, or Fitbit for determining real-time athletic strain or recovery might not be the best approach.

While wearable devices offer a convenient way to track various metrics, these studies suggest they should not be the sole source of information for athletes and coaches.

Instead, a balanced approach that combines technology with traditional methods of monitoring training and recovery seems to be the most effective strategy for athletes striving for peak performance.

Are Fitness Trackers and Running Watches Accurate? What The Latest Studies Reveal 2

Why You Should Use Rate Of Perceived Exertion

Heart rate monitoring and Rate of Perceived Exertion (RPE) serve similar yet distinct purposes in training. Both methods have benefits and should be used complementarily for a comprehensive training strategy.

RPE offers a nuanced approach to training that emphasizes personalization and adaptability.

By grading workout intensity on a scale of 1-10, RPE allows runners to account for variables often overlooked by technology, such as changes in terrain, weather, and personal energy levels.

This subjective measure of effort acknowledges that many factors, not just physical capacity, influence performance. For instance, running the same distance on a hilly trail can be more demanding than on a flat road, and RPE accommodates this difference.

Furthermore, RPE empowers runners to adjust their training based on their body’s signals.

If fatigued, a pace that usually feels moderate may feel more strenuous, and RPE allows for this adjustment, promoting a healthier and more sustainable training approach.

Are Fitness Watches Accurate?

Fitness watches have revolutionized how we approach health and fitness. They excel in logging activities, from daily steps to long run sessions, providing a tangible record of physical exertion over time.

However, the true value of these devices lies in their ability to interpret data over time. Looking at trends in HRV, RHR, sleep quality, and stress markers offers a deeper insight into one’s health than any single measurement could.

While metrics like strain, which primarily tracks cardiovascular output, may have limitations, especially in activities like weight training, they still provide useful information.

Although not always precise, the interpretation of recovery offers a general guide to how well the body copes with stress and fatigue.

While current research highlights certain limitations in fitness watch technology, it’s important to recognize the potential for improvement. We expect these devices to become more accurate and reliable as technology advances.

Additionally, larger and more comprehensive studies are needed to provide clearer insights into the effectiveness of fitness watches.

While fitness watches have limitations, they should be considered complementary to other health and fitness tracking methods, such as subjective measures like RPE.

Together, these tools offer a comprehensive picture of one’s health, aiding in a more informed and personalized approach to fitness and well-being.

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Ben is a qualified Personal Trainer and Sports Massage Therapist with a particular interest in running performance and injury. He has spent the last 9 years working with runners at his clinic in Brighton. Ben is a keen runner and avid cyclist. Evenly splitting his time between trail running, road biking, and MTB.

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