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As heart-rate tracking technology improves, it’s important to adjust how we use it in our training. Wrist-worn, optical heart-rate sensors offer convenience, but they aren’t perfect. Understanding their limitations—and how to use the data effectively—is key to benefiting from these metrics without getting overwhelmed by them.

Starla Garcia, a 31-year-old runner, found that her Garmin Forerunner 235 often gave her inflated heart-rate readings during easy runs. While external factors like temperature can influence heart rate, research shows that Garcia isn’t alone in experiencing these inaccuracies. A 2017 study revealed that wrist-worn devices were less accurate for certain groups, including men, people with darker skin tones, and those with higher body mass indexes. Environmental factors like altitude and weather conditions can also distort heart-rate readings, according to Neal Henderson, head of sports science at Wahoo Fitness.

So, while tracking heart rate with a wrist device is certainly convenient, it may not be the most reliable way to guide your training. To better understand this, we need to look at how these devices actually work.

How Heart-Rate Tracking Devices Work

There are two primary types of heart-rate monitors: chest straps and wrist-based devices. Chest straps typically measure electrical conductivity in the heart, while wrist and arm devices measure blood flow using optical sensors.

Wrist devices use a method called photoplethysmography (PPG), which detects changes in blood flow. Since blood absorbs green light and reflects red light, optical sensors in these devices emit green light to detect blood flow in the wrist. The more blood flow there is, the more green light is absorbed, allowing the device to calculate heart rate based on these fluctuations.

While this method works fairly well, it’s not as accurate as chest straps. A 2017 study in JAMA Cardiology showed that wrist-based devices often provide less accurate readings than chest straps, especially during exercise. The accuracy of the Apple Watch was better compared to some other wrist-worn devices, but it still fell short of a chest strap.

Similarly, a 2019 study confirmed that chest straps, like the Polar H7, were the closest in accuracy to an electrocardiogram (ECG), while wrist devices like the Apple Watch and Fitbit performed well, but not as accurately.

The Limitations of Wrist-Based Heart Rate Tracking

While wrist-based devices offer greater convenience, they have several drawbacks when it comes to accuracy. One major issue is that many runners rely on heart-rate data to establish training zones, often using maximum heart rate as a baseline. However, determining your max heart rate through a test can be challenging and even risky for some people, such as those new to exercise or with existing health conditions.

Additionally, wrist-based devices are not always effective for all demographics or activities. For example, optical sensors may struggle with darker skin tones or tattoos. High humidity, altitude, and biomechanical changes can also lead to inaccurate readings. Some research suggests that the green light used by these devices isn’t ideal for everyone due to its wavelength, which is more readily absorbed by melanin in darker skin tones.

Alternative Ways to Use Heart Rate Effectively

Despite the limitations of wrist-based heart-rate monitors, these devices can still be valuable tools for personalizing your training. The key is understanding the data, using it appropriately, and not letting it dictate every aspect of your workout.

Training

If you want to track heart-rate data for training purposes, using a chest strap will provide more reliable information. However, it’s essential to interpret this data alongside how your body feels. Running coach Kaitlin Goodman advises runners to trust their bodies. “If your watch says your heart rate is 180 and you feel comfortable, trust yourself,” she says.

Instead of focusing on max heart rate, some runners, like David Roche, prefer to use lactate threshold heart rate (the point at which lactate builds up faster than it can be cleared). This method helps determine the intensity of exercise and can provide more accurate training zones based on individual fitness levels.

Recovery

Heart-rate variability (HRV) is another useful metric for tracking recovery. Devices like Whoop measure HRV to gauge your overall recovery status. A higher HRV indicates better recovery. If your device doesn’t track HRV, you can monitor your resting heart rate (RHR), which is often measured accurately by wrist-based devices. Elevated RHR can be a sign that you need more rest.

Nutrition

Garcia, a registered dietitian, used heart-rate data to monitor her hydration and nutrition levels during training. After noticing discrepancies in her device’s readings, she switched to a chest strap, which gave her more accurate data. During Grandma’s Marathon, for example, Garcia used her heart rate readings to adjust her electrolyte intake based on how she felt, ultimately helping her maintain control over her performance despite rising temperatures.

Where Is Heart Rate Tracking Headed?

Heart-rate tracking technology is still evolving, and manufacturers are working hard to improve accuracy across all skin tones and demographics. Companies like Coros, Apple, and Garmin are investing in more inclusive and accurate optical heart-rate sensors.

Despite its current limitations, heart-rate tracking is a valuable tool when used with care. As Garcia’s experience shows, heart-rate data can help athletes fine-tune their training, recovery, and nutrition strategies. With continued improvements in technology, we can expect even more reliable and useful data to guide our running performance in the future.

The Fitbit Sense is a versatile device that blends fitness tracking with advanced wellbeing features, making it an excellent choice for anyone looking to improve their overall health. While it may not provide the deep dive into training metrics that some athletes might seek, it offers a comprehensive set of functions aimed at monitoring both physical and mental wellness.

A Sleek and Durable Design

The Fitbit Sense is a step up from its predecessor, the Fitbit Ionic, in both design and functionality. The watch features a sleek graphite steel case and is equipped with durable Gorilla Glass, ensuring it can withstand the wear and tear of daily use. The silicone wristband is comfortable, and the bold, colorful display stands out, making it both stylish and functional.

Fitness Features: Basic but Reliable

For those seeking detailed training insights, the Fitbit Sense might fall short. It doesn’t offer advanced interval training or heart rate zone management, limiting its usefulness for serious athletes. However, it does cover the basics—providing reliable metrics like time, pace, and distance for everyday running or walking sessions.

The heart rate monitoring is fairly accurate, though not as precise as a chest strap. It provides a decent guide, but there is a slight delay when changing paces. GPS connectivity is quick and reliable, even in areas with moderate urban coverage.

While the watch offers access to 20 different training modes through a premium subscription, the lack of onboard storage means you’ll need to bring your phone along to make the most of those guided workouts.

Smartwatch Features: Practical and Convenient

As a smartwatch, the Fitbit Sense offers a good mix of functionality, including call and message notifications, Fitbit Pay for contactless payments, and Alexa voice control. The ability to dictate responses to messages using the built-in microphone is a nice touch, especially when you’re on the go.

The device also includes several health-tracking features, such as blood oxygen saturation (SpO2) monitoring and skin temperature readings during sleep. While these features may seem niche, they provide additional insight into your health, with SpO2 being particularly relevant during the current pandemic as a potential indicator of respiratory issues.

The skin temperature feature works by tracking your baseline temperature over a few nights, then monitoring fluctuations. This could be useful for identifying early signs of illness or changes in your health.

Stress Management: A Unique Feature

One of the standout features of the Fitbit Sense is its EDA (electrodermal activity) scan, which measures stress by analyzing sweat gland activity. This feature is the first of its kind in a smartwatch, and it can be a valuable tool for tracking your stress levels throughout the day. By combining the EDA scan with mindfulness meditation sessions and mood tracking, you can get a clearer picture of your stress patterns.

However, while the EDA scan is an innovative feature, its practical usefulness may vary. Some users may prefer to rely on their own feelings of stress, such as sweaty palms, rather than tracking data on a screen.

Usability and Functionality Concerns

While the Fitbit Sense has a lot of great features, its button functionality is a bit of a hassle. Instead of traditional physical buttons, the Sense uses a capacitive groove that you tap to interact with the device. This setup can be inconsistent—sometimes it responds immediately, but other times it requires multiple presses or a firm touch. Additionally, the sensitive nature of the groove can sometimes trigger unintended actions, which can be frustrating.

Another downside is that many of the more advanced features, like guided workouts and access to training modes, require a premium subscription. The device itself costs $499.95, and the additional $8/month for Fitbit Premium might be a deterrent for some users. However, it’s worth noting that the Sense comes with six months of Fitbit Premium free, so you can test the service before committing.

Final Thoughts

The Fitbit Sense stands out as an excellent wellness tracker with a range of features aimed at improving both physical and mental health. Its design is sleek, and its fitness capabilities are more than adequate for casual runners or those focused on overall wellness. However, for those seeking advanced training metrics, it may not be the best choice.

For anyone interested in maintaining a balanced, healthy lifestyle with a mix of fitness tracking and stress management, the Fitbit Sense is definitely worth considering. While it may not replace a dedicated fitness watch for serious athletes, it offers enough versatility and advanced features to make it a top contender for those who want a holistic approach to their health.