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Fitness tracking might sound like a ubiquitous term nowadays. A plethora of devices and apps aim to get you off the couch and in shape with tailored insights. However, tracking one’s health was not as accessible as it is currently, a few decades ago. 

From the early physical pedometers to inconspicuous smart rings, the field has come a long way in the digital health era. We’ll track the journey of fitness trackers in this article, and glimpse at what the future holds.

A centuries-old concept

Fitness trackers adopt a range of shapes and sizes, but they share a common feature: step count. This can be considered the most basic form of fitness tracking and owes its origins to Leonardo da Vinci. Indeed, the polymath proposed a waist-worn device to count the number of steps back in the 16th century, perhaps making this the first description of a pedometer, or stepcounter. But this was only conceptual.

The first actual pedometer can be traced back to the 1700s, attributed to either Swiss horologist Abraham-Louis Perrelet or Thomas Jefferson, depending on the source. The precursor to current fitness trackers appeared much later. In 1965, Dr Yoshiro Hatano presented the Manpo-kei device, or ‘10,000 steps meter’ in Japanese. The researcher proposed that taking 10,000 steps daily would be beneficial for one’s health, and that goal has generally stuck with fitness trackers ever since. 

In the modern era, fitness trackers can be broadly grouped into four categories. The first category includes simple clip-on devices that provide simple metrics, such as stepcounts, and were early mass market products. The second category, fitness trackers, are consumer-grade, usually wrist-worn devices that monitor steps, sleep or even stress levels. The third category includes smartwatches. These devices usually include all of the features of fitness trackers but are more feature-rich, serving as an extension to your smartphone, mirroring its notifications and allowing some phone controls.  The third category includes chest straps and sports watches, which are generally targeted at athletes and outdoor activities, often with GPS and more precise sensors. The fourth category involves apps, rather than devices, which can track steps from your phone itself or can serve as fitness diaries to track your activities manually.

The evolution of modern fitness tracking devices is marked by a number of milestones that we look at in the next section. 

Milestones of modern fitness trackers

Fitness tracking really propelled with the “Fitbit phenomenon”, as the company’s first clip-on trackers in 2009 helped turn stepcounting into a social, consumer habit. In subsequent years, the brand iterated from clips to wristbands and ultimately to smartwatches as sensors and batteries got smaller. 

In parallel, other companies also tapped into the growing trend. Garmin and Polar released sportswatches and chest straps with more athletic- and outdoors-oriented devices with GPS tracking, altitude and chest straps for more accurate metrics. Companies like Pebble and Apple released their own versions, this time as smartwatches with simple fitness tracking features.

It was Nike’s FuelBand from 2012 that popularised the gamification of exercise to motivate and engage fitness enthusiasts of the digital age. The wristband-like device enabled users to undertake weekly challenges and compete with their friends with a social sharing feature. This approach indicated that behaviour change could be engineered into wearables. 

The next leap was brought forth in 2014 by Fitbit with the Fitbit Charge HR’s ability for 24-hour heart rate monitoring. This was an early glimpse at the evolution of trackers from simple step counters to continuous physiology monitors. The company pursued this endeavour with the rollout of detailed sleep tracking features in 2017. This turned overnight data into actionable insights, helping people improve their sleep hygiene. 

Consumer-grade wrist-worn trackers went fully clinical starting in 2018. The Apple Watch Series 4 and Withings Move ECG, released a year later, brought ECG monitoring to the wrist, even bringing the ability to detect atrial fibrillation. indicated a future where smartwatches themselves would become the centre of fitness and health tracking. We are living in that future now.

From stepcount to whole-body analyses

Nowadays, as many as one in five people use a smartwatch or fitness tracker. But if you account for fitness apps, the share is likely to go up. Even smartphones can monitor one’s steps and physical activity. 

However, they cannot perform as much tracking as a dedicated device can. This is because with technological development and the miniaturisation of sensors, wrist-worn devices can monitor more metrics while being in contact with the user’s skin. 

In particular, photoplethysmography (PPG) has elevated fitness tracking. This non-invasive optical technique provides measurements based on changes in light intensity as a result of blood flow. PPG sensors can provide readings such as blood pressure without a cuff and blood-oxygen saturation (SpO₂), resulting in a sleeker and more practical fitness device. 

SpO₂ measurements became standard across major lines, from Apple to Fitbit, in 2020, partly driven by interest in respiratory monitoring during the COVID-19 pandemic. In the next wave, stress analyses and heart-rate-variability (HRV) took centre stage, moving wearables closer to mental-health and recovery use cases.

With such metrics becoming more common in smartwatches, these devices have turned into the default fitness tracker. The acquisition of Fitbit by Google in 2019 was an early indication of where the field was headed. Individual fitness trackers are now rarer, while only athletes wear chest straps and sport clothing embedded with sensors. For their part, fitness apps generally function as companions to smartwatches to gain deeper insights from the metrics.

With the wealth of personalised metrics from smartwatches, deeper insights could be drawn with the help of artificial intelligence (AI). Around 2021–2022, wearable companies started to provide personalised, AI-driven guidance. For example, Fitbit introduced the Daily Readiness Score, which aggregates activity, HRV and recent sleep data to help the user decide whether to prioritise physical workout or recovery.

Fitness trackers have evolved from mere stepcounters to literal whole-body analysing devices. They are capable of giving the general audience highly personalised metrics, but there’s more lying ahead for the future of these devices.

What’s next for fitness tracking?

From its humble origins to its current state, fitness tracking might seem to have peaked, but this is far from the case. The ubiquity and convenience of fitness tracking make trackers apt for turning the patient into the point-of-care without much effort.

With technological development and further miniaturisation of sensors, fitness trackers will be able to perform more noninvasive measurements. Blood pressure monitoring was an early indication of this, with the next frontiers being noninvasive glucose monitoring and hydration sensors. These could be integrated in familiar devices such as smartwatches or smart rings, while new, less conspicuous accessories could become more popular such as skin patches and, eventually, implantable monitors.

More than just measuring health metrics, the devices and the algorithms of their companion apps will provide ever more personalised insights to users. This can affect behaviour change, nudging people to adopt healthier habits.

The wealth of personal health data from such devices will need to be integrated with electronic health records for them to make valuable contributions. There will thus need to be a gradual change in accepting such means of health monitoring and their integration within healthcare systems.

Written by Dr. Bertalan Meskó & Dr. Pranavsingh Dhunnoo

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