On-going development in fitness and health devices, coupled with advances in data analytics continue to broaden the depth of information we get from our wearable tech and activity trackers.
This innovation in wearable tech and data processing continues at a rapid pace. For instance, in 2019, wearable devices incorporated 4.1 sensors on average compared to 1.4 in 2013.
Beyond the traditional accelerometers and GPS sensors, the latest generation of devices contain sensors that include thermometers, electrocardiogram (ECG), microelectronic mechanical (MEM) and electrodermal activity (EDA) monitors, to name a few, which all enable more advanced tracking capabilities.
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Heart-rate tracking
But few sensors have had the same impact as the optical heart rate sensor, which is now included in a wide range of wearables, from entry level to the most advanced devices.
This tracking capability changed the game for health and fitness tracking because it offered an unobtrusive means to measure your heart rate 24/7.
While this is a great way to track and analyse daily activity and estimate total energy expenditure throughout the day, the ability to measure your heart rate when you are active and, perhaps more importantly, while you sleep, helps to deliver a treasure trove of health and fitness-related insights.
With this data, our devices can make recommendations about the ideal intensity to train at or even suggest an extra rest day to improve recovery. Certain indicators like tracking our resting (or waking) heart rate over time can also help us pre-empt a possible infection or overtraining.
Wearable devices can even identify a potential cardiovascular event like a heart attack – Fitbit released its Irregular Heart Rhythm Notifications feature on certain devices in April 2022 that uses sensor data to identify atrial fibrillation (AFib).
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Heart rate variability
Heart rate variability (HRV) is a key metric that can deliver insights about your training and recovery, as well as your overall health and current stress levels.
Heart rate sensors measure the variability in time between consecutive heartbeats (typically measured in milliseconds) because your heart does not beat with a perfect metronomic rhythm. While these variations in your heart rate are healthy and normal, low heart rate variability can indicate higher stress levels.
As your heart rate activity is regulated by an involuntary part of your nervous system called the autonomic nervous system, any changes in your heart beat can offer insights into how well your system is regulating itself in response to stressors like exercise, psychological stress, environmental factors or situational demands like work.
In general, higher HRV is associated with parasympathetic dominance within your autonomic nervous system, which is a sign that your body is balanced and in the relaxed ‘rest-and-digest’ mode. In this state, your heart rate decreases and your heart beats in response to your immediate needs. As such, HRV increases.
On the other hand, a lower HRV is typically associated with elevated sympathetic activity within your autonomic nervous system, which may indicate high stress levels or that you are in high-alert ‘fight-or-flight’ mode. When your sympathetic nervous system is more active and dominant, your heart rate typically increases and it beats in a more regular rhythm, which means HRV decreases.
Ideally, you want to create balance between the activity of these two branches of the autonomic nervous system. In many devices, HRV values are also used to calculate various physiological measurements such as stress score, lactate threshold, and Body Battery (available on select Garmin devices).
Respiration rate
Various devices from Fitbit, Garmin, Apple and Google (Android) track your respiration or breathing rate – a measurement of your average breaths per minute.
This metric is another primary vital sign (along with heart rate, blood pressure, and body temperature) and can indicate exercise-induced fatigue, rising stress levels or even the onset of various health conditions such as potential adverse cardiac events or various respiratory conditions.
A typical resting respiration rates is 12-20 breathes per minute and can rise to 40-50 times per minute during intense exercise or activity due to increased oxygen demands needed for energy production.
Your breathing rate is also closely tied to HRV as the length of time between consecutive heartbeats shortens slightly as you inhale and lengthens as you exhale.
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SpO2 sensor
Sp02 sensors send and receive a light beam through your skin and blood vessels to measure the oxygen saturation level in your blood. This information is generally shared via a companion app to provide insights about general wellness and fitness. A healthy oxygen saturation level ranges between 95-100%.
For example, the Fitbit Charge 5 features a relative SpO2 sensor, which powers Fitbit’s Estimated Oxygen Variation Graph in the Fitbit app and may indicate variations in your breathing during sleep. Other brands that now include Sp02 sensors in select devices include Huawei, Apple, and Garmin.
Your Sp02 level indicates how well the body distributes oxygen from the lungs to the cells, and may can serve as an important indication of your health cardiorespiratory health and overall fitness.
A lower reading could indicate conditions like sleep apnea or hypoxemia, which is a potentially dangerous condition where the body has difficulty delivering oxygen to cells, tissues and organs.
Real-time form feedback
Smart clothing and apparel represent another frontier in the wearables game experiencing rapid innovation and technology-based advances.
Embedded sensors in running shoes, like the Under Armour Flow Velociti Wind 2 and UA HOVR Phantom, among others, connect to the UA MAPMYRUN™ app to track and analyse your running metrics to help make you a better runner with form queues and recommendations.
Similarly, Nadi smart exercise tights correct a wearer’s alignment using haptic feedback in the form of subtle vibrations determined from the sensors and the companion app to correct your body positions and form.
Disease detection
Numerous third party providers are developing apps that use data from common wearable devices like Android or Apple smartwatches and Garmin and Fitbit devices to gather and analyse key metrics and identify various health-related conditions.
For example, an app called MyPHD analyses collected data and in a study published in Nature Medicine, was able to detect 80% of pre-symptomatic and asymptomatic infections.
Fitbit also collaborated with The Scripps Research Institute and Stanford Medicine on research to determine if tracking changes in heart rate, activity, and sleep could help detect, track, and contain Covid-19.
Author: Pedro van Gaalen
When he’s not writing about sport or health and fitness, Pedro is probably out training for his next marathon or ultra-marathon. He’s worked as a fitness professional and as a marketing and comms expert. He now combines his passions in his role as managing editor at Fitness magazine.
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