Wrist-worn fitness trackers that monitor steps and heart rate have evolved significantly, once hailed as cutting-edge technology. Today, these wearables are increasingly high-tech, offering features like personalized workout programs and the ability to monitor stress and sleep quality.
Since 2015, we’ve been rigorously testing 46 different fitness trackers while running, walking, swimming, cycling, sleeping, and more. Our assessment focused on accuracy, ease of use, and comfort. Although no tracker perfectly recorded every metric, we found that the Fitbit Inspire 3 stands out as the best option for most users. It combines a simple design with a robust set of features, including metrics for distance traveled, step count, heart rate, and estimated calories burned.
How we tested
We paid close attention to battery life, comfort, ease of menu navigation, and customizability.
We wore each device for two days straight, comparing step-count data to that of a pedometer we know to be precise.
We walked, jogged, and ran with each fitness tracker to see how well it documented workout data.
We performed two tests with each device using a chest-strap heart-rate monitor as a comparative control.
Fitbit Inspire 3
The best fitness tracker
This easy-to-use tracker is comfortable to wear all day and provides accurate measurements, without too much clutter on the homescreen.
The Fitbit Inspire 3 emerged as the most accurate fitness tracker for step count and ranked highly in all other tests we conducted. Its touchscreen display, while only 1.5 inches tall, is easy to navigate thanks to vibrant colors and clear text and icons. The sleek, half-inch band feels lightweight and comfortable during workouts and daily activities, weighing just 0.32 ounces—lighter than a standard USB flash drive.
Fitbit offers a free app that allows users to connect with others, log information for stress management, and delve into data like heart-rate history. A premium version of the app is available for $10 per month or $80 per year, granting access to additional features, including apps like Calm for sleep and meditation. The Inspire 3 boasts a battery life of up to 10 days before requiring a charge, although in our experience, it fell a bit short of that expectation.
- Battery life: Up to 10 days
- Water resistance: Yes, up to 50 meters
- GPS: Available when connected to a phone
Fitbit Charge 6
More features, including built-in GPS
The latest version of the Charge series continues a tradition of accurate activity tracking, but many of the new additions require Google integration.
The Fitbit Charge 6 introduces several enhancements over the Charge 5, which we previously recommended as a strong runner-up. The most significant upgrade is the addition of a haptic side button, making screen navigation smoother and more intuitive compared to swiping on the touchscreen, which we found to be occasionally unresponsive.
The Charge 6 also features built-in GPS, a capability not available on the Inspire 3, along with access to Google Maps, Google Wallet, and YouTube Music (with a subscription). However, in our distance tracking tests, the Inspire 3 outperformed the Charge 6.
- Battery life: Up to 7 days
- Water resistance: Yes, up to 50 meters
- GPS: Built-in
Apple Watch SE (2nd generation)
A smartwatch and fitness tracker in one
The Apple Watch SE delivers some of the most precise readouts and—with a mobile plan—can be used for calls and messaging. But its battery life is much shorter than that of our Fitbit picks.
The second-generation Apple Watch SE boasts a vibrant, clear display and the most intuitive touchscreen among the devices we tested. Even without an iPhone connection, users can access a vast library of apps. In terms of performance, the Apple Watch SE—our top budget smartwatch choice for iPhone users—accurately tracks heart rate, steps, and distance. However, for those looking to simply track their pace and distance while running, the Apple Watch SE may feel like overkill, particularly given its higher price point and limited battery life.
- Battery life: Up to 18 hours
- Water resistance: Yes, up to 50 meters
- GPS: Built-in
The research
Why you should trust us
Who this is for
How we picked and tested
How the fitness trackers we tested fared
Our pick: Fitbit Inspire 3
Runner-up: Fitbit Charge 6
Also great: Apple Watch SE
Other good fitness trackers
The competition
Sources
Why you should trust us
To gain a deeper understanding of the various components and accuracy of fitness trackers, we consulted cardiologists, professors specializing in device accuracy, and running coaches, as well as physicians who regularly utilize wearables in their assessments. Their insights helped us evaluate the effectiveness and reliability of these devices in monitoring health metrics.
Who this is for
Fitness trackers provide valuable insights into how you move throughout the day, making them essential for individuals looking to set goals for increased daily activity and gain a clearer picture of their overall health.
These wrist-worn devices primarily track the swinging of your arm, which closely corresponds to your legs’ movements when walking or running. However, since humans engage in many activities beyond just walking and running, these trackers can misinterpret other arm movements—like folding laundry or clapping—as “steps.” The commonly referenced goal of 10,000 daily steps appears arbitrary, yet increasing movement throughout the day is generally beneficial.
There are also specialized GPS running watches and smartwatches that deliver similar health-related information, often with added features. The distinctions between fitness trackers, GPS running watches, and smartwatches are becoming increasingly blurred. Typically, fitness trackers are less bulky and more affordable than their GPS and smartwatch counterparts. They also tend to boast longer battery life, often lasting a week or more between charges, while smartwatches usually require daily charging.
Many fitness trackers, GPS running watches, and smartwatches come with companion apps that track additional data, such as sleep patterns, hydration levels, and menstrual cycles. According to Aric A. Prather, a professor of psychiatry at the University of California San Francisco Weill Institute for Neurosciences, most wearable devices can accurately estimate total sleep time and sleep fragmentation, but are less reliable when it comes to assessing sleep architecture, such as the duration of deep sleep.
It’s important to note that none of the wearables discussed in this review are classified as medical devices, and the data they collect is not regulated or protected in the same manner as other health data.
If you have concerns about starting a new exercise regimen or suspect a health issue, it’s crucial to consult a medical professional. Additionally, if you are worried about abnormal heart rates, do not rely solely on an activity tracker to manage your health condition.
The limitations of fitness trackers
Approach certain metrics from fitness trackers with caution. These devices should not replace consultations with medical professionals regarding any cardiovascular symptoms to ensure proper diagnosis and treatment, as emphasized by Meagan Wasfy, a sports cardiologist at Mass General Brigham. However, they can offer a general overview of your health. For instance, as individuals become more fit, their resting heart rate typically decreases because a stronger heart pumps oxygen-rich blood more efficiently, according to Seth Martin, a professor of medicine at Johns Hopkins specializing in cardiology. “Fitness trackers can provide valuable insights into heart rate trends over time and store this information for later review.”
GPS accuracy—whether a tracker has its own onboard GPS or relies on your smartphone—can be adequate but is rarely perfect. More advanced metrics, such as breathing rate, blood oxygen saturation, and atrial fibrillation (A-fib) detection, should be viewed as guides rather than substitutes for medical assessments.
Most fitness trackers offer an estimated calorie burn tally based partially on your basal metabolic rate. Andrew Jagim, PhD, director of sports medicine research at Mayo Clinic Health System, notes that each company employs its proprietary algorithm for these calculations. Some may rely on heart rate data, while others incorporate accelerometer information.
Max Paquette, an associate professor at the University of Memphis who advises athletes on performance optimization, cautions that trackers can sometimes disconnect users from their bodies. “They become overly reliant on data, neglecting to listen to their own physical sensations. They prefer to have their watch tell them what they’re experiencing, which I view as a disadvantage. You can learn a lot from your body while training.” Nicole Hagobian, a sports psychology consultant at California Polytechnic State University, adds that for individuals who fear failure and struggle with negative social comparisons, a tracker can introduce anxiety and unnecessary stress during workouts.
To monitor data like heart rate, fitness trackers—and other wrist-worn devices, such as GPS running watches—utilize photoplethysmography. This technology employs light (most commonly green LEDs, as they effectively measure hemoglobin) to assess changes in blood volume at the wrist. However, this method is not without its quirks. The way a tracker is worn—its position on the wrist and the tightness of the band—can influence readings. Research has explored additional factors, such as skin tone, body hair, and tattoos, which may affect the accuracy of wrist-based heart rate measurements. Findings related to skin tone, in particular, have produced mixed results.
How we picked and tested
In this guide, we focused on evaluating the key features that potential users of dedicated fitness trackers typically seek: step count, distance tracking, and resting heart-rate readouts. We also considered factors such as smaller bands and displays that resemble traditional fitness trackers more than smartwatches, along with price points. Additionally, we tested the daily activity tracking capabilities of more expensive devices like the Samsung Galaxy Watch 5, Apple Watch SE, and the screenless Whoop 4.0.
Our primary goal was to identify devices that are accurate, dependable, and durable.
Throughout our testing, we aimed to answer the following questions:
How easy is the fitness tracker to use and live with? Since these devices are designed to be worn all day, we prioritized comfort, wearability, and user-friendliness—both of the device itself and its companion app. We also paid close attention to battery life and syncing capabilities.
How well does it track activities? To assess the accuracy of the trackers in recording all-day step counts, we wore two devices simultaneously—one on each wrist—for two consecutive days, switching wrists on the second day. We compared their step-count readings with those from a reliable Ozo Fitness SC 3D Digital Pedometer we had on hand.
How well does it record workouts? For each device, we evaluated how accurately they estimated distance traveled by walking one mile on a treadmill.
For any device designed to track active heart rate during workouts, we conducted two separate tests on the treadmill: a steady-state run lasting five minutes at an easy pace, followed by a six-minute session that included a walk, jog, and run for two minutes at each intensity. We compared the heart rate readings from the fitness trackers against those from a Polar H10 heart-rate sensor with a chest strap. Additionally, we evaluated the resting heart rates recorded by each fitness tracker in comparison to the Polar H10, ensuring a comprehensive assessment of their accuracy in measuring heart rate during both active and resting states.
How the fitness trackers we tested fared
The first column displays the accuracy of each tracker in measuring the distance covered (1 mile) during our treadmill workouts. The second column tabulates the step count error percentage, comparing the readings from each tested fitness tracker with those from our reliable pedometer. It’s important to note that many wrist-worn fitness trackers tend to inflate all-day step counts, as they often register certain arm movements as “steps.”
The percentages in the third column indicate each company’s advertised battery life, while the final column reveals how much battery remained after two days of continuous use. This comprehensive breakdown provides valuable insights into the performance and reliability of each fitness tracker.
Fitness tracker performance
Here’s how the fitness trackers we tested—or retested—in 2023 performed, with our top picks highlighted in bold. The Fitbit Inspire 3 and Charge 5 stood out for their accuracy in tracking steps and distance, both ranking among the most precise devices. Their battery lives fell in the middle range compared to other trackers. The Apple Watch SE also demonstrated commendable performance in tracking steps and distance; however, it had the shortest battery life of all the devices we tested, highlighting a trade-off for its smartwatch capabilities.
Our pick: Fitbit Inspire 3
Fitbit Inspire 3
The best fitness tracker
This easy-to-use tracker is comfortable to wear all day and provides accurate measurements, without too much clutter on the homescreen.
The Fitbit Inspire 3 delivers precise readings, impressive battery life, and a wealth of features designed to accommodate various health goals. In some respects, it serves as a throwback, featuring a simple interface and compact size that we appreciated. A flashy display and an abundance of specialized health metrics don’t necessarily guarantee a product’s ability to handle fundamental tasks, such as accurately measuring step count and resting heart rate—basic functionalities that some users prioritize in a wearable.
This device is particularly user-friendly. The display activates with a simple swipe across the screen. When synced with the Fitbit app, the home screen can be customized with various backgrounds displaying time, heart rate, step count, and other vital information. A swipe up from the home screen reveals additional metrics, including distance traveled and SpO2 (blood oxygen) levels, while a right swipe navigates to timers, exercise programs, and other features.
Swiping down from the home screen provides access to settings that allow you to customize notification frequency and general settings, including screen timeout duration and brightness options—dim, normal, and max. Prior to changing these settings, informative warnings appear, indicating how adjustments may impact battery life, ensuring users are aware of potential trade-offs.
The Fitbit Inspire 3’s interface is intuitive to use.
The Fitbit Inspire 3 app is equally user-friendly. Fitbit’s free app is intuitive and filled with tips and insights on specific metrics, making it easy to navigate. It connects you to a large, active social network that can help motivate you to achieve your goals. For those seeking more features, there’s Fitbit Premium, the enhanced version of the app, available for $10 per month or $80 annually (first-time Premium users can activate a six-month trial subscription). This option includes perks like guided workouts and audio mindfulness sessions.
Through the free app, you can manually track blood glucose levels and connect to your phone’s GPS. It also allows you to set reminders to move, establish fitness goals, and log important details like heart rate, sleep, and activity for a stress management score. Additionally, the app helps you monitor food and water intake. While these features are not essential, they serve as useful add-ons presented in clear language for anyone interested in enhancing their nutritional health tracking.
Since Google acquired Fitbit in 2021, the latest Fitbit devices are fully integrated with Google accounts. New users purchasing certain wearables (including our runner-up pick, the Fitbit Charge 6) must sign up for Fitbit using a Google account. Existing users can still link new Inspire 3 devices to their current Fitbit accounts. According to a company representative, support for existing Fitbit accounts will continue until at least 2025, after which all Fitbit owners will need to use a Google account for their devices. The company plans to communicate this transition transparently through notices in the Fitbit app, emails, and help articles.
New Fitbit users must register with a Google account and accept Google’s terms and services, which encompass Google’s privacy policy. These terms detail how Fitbit data is collected, stored, and shared with third parties. A Google representative confirmed that existing Fitbit account users who choose not to migrate before 2025 can continue to use their Fitbit under the original terms of service and privacy policy.
In terms of performance, the Fitbit Inspire 3 is the most accurate tracker and boasts impressive battery life. In our step count accuracy tests, it deviated by just 0.32% from our pedometer readings over a two-day period—the best accuracy among all tested fitness trackers. During a one-mile distance accuracy test, the Inspire 3 recorded an impressive deviation of only 0.03 miles.
Battery life also showed promising results; while some testers rated it as average, others experienced exceptional longevity. After wearing the Inspire 3 for two days and two nights, including multiple recorded workouts and auto-detected activities, we found it lasted approximately seven days before requiring a charge, despite being advertised for 10 days.
One tester, who owns both the Inspire 3 and the Fitbit Charge 5, noted that they need to charge the Charge 5 much more frequently, stating, “I cannot remember the last time I plugged in my Inspire 3.” Additionally, in tests measuring resting heart rate, the Inspire 3 recorded a deviation of just 1 bpm, making it one of the most accurate devices we evaluated.
The free version of the Fitbit app is easy to navigate and has a wealth of information to track your health.
The Fitbit Inspire 3, like all Fitbit products, comes with a one-year warranty for added peace of mind. Users can also customize their device with additional bands available in various colors and materials, including stylish stainless steel options, as well as a convenient clip-on alternative—all offered at an additional cost. This customization allows you to personalize your Inspire 3 to fit your style while maintaining its functionality.
Flaws but not dealbreakers
The Fitbit Inspire 3 features a flexible silicone band that fastens with a plastic buckle and tang, reminiscent of how a belt buckle closes. While this design is common among fitness trackers, we found that it sometimes took a few attempts to secure properly. The slim profile of the Inspire 3 can be a drawback in this regard, as the band doesn’t lay as flat as that of a thicker device like the Apple Watch SE. Additionally, the tang feels somewhat flimsy, making it challenging to keep in place during adjustments on the wrist.
During our testing, we noticed that occasionally, when swiping through the touchscreen, we applied too much pressure, inadvertently activating modes we didn’t intend to or bringing up screens that required extra swipes to exit. This could be seen as a minor downside of the tracker’s minimalist design and smaller-than-average display.
In one of our tests, the battery life fell about three days short of the advertised 10 days. While this is not ideal, it’s still a performance level that isn’t terrible, especially given the functionality it offers.
Runner-up: Fitbit Charge 6
Fitbit Charge 6
More features, including built-in GPS
The latest version of the Charge series continues a tradition of accurate activity tracking, but many of the new additions require Google integration.
When it comes to tracking distance, the Fitbit Charge 6 excels with its built-in GPS—an advantage that the Inspire 3 lacks. Its predecessor, the Charge 5, was previously a recommended pick in this guide and remains widely available. However, several reviewers have noted challenges with syncing the Charge 5 to the Fitbit app. In contrast, we encountered no such issues with the Charge 6, although a Google account is required for use, even for those who already have the Fitbit app. The Charge 6 also features a convenient haptic side button, making screen navigation much easier.
The Charge 6 is highly reliable for tracking. Historically, the Fitbit Charge series has been dependable in monitoring steps and distance. In our one-mile distance test, the Charge 6 was off by only -0.02 miles and achieved an error rate of 1.3% in our step-count evaluation, performing just below our top pick. After two days of continuous use, the battery was at 68%, slightly below the company’s estimate of lasting seven days.
Easier-to-Use Display and Band: Many Fitbit Charge users had expressed frustration over the absence of a haptic side button on the Charge 5, so its return in the Charge 6 is a welcome improvement. This small enhancement significantly simplifies screen navigation, especially during runs or when wearing gloves, as the touchscreen may not always respond optimally in those situations. The Charge 6 features a thick, flexible silicone band that is easier to adjust compared to the Inspire 3’s slim band, which can sometimes be challenging to secure. The vibrant AMOLED display on the Charge 6 is bright and clear both indoors and outdoors, and the device weighs just 1.02 ounces.
More Exercise Options: The Charge 6 comes equipped with an impressive 40 exercise modes, a significant upgrade from the Charge 5, which supported only six modes. While you could switch different exercises onto the Charge 5 through the app, it had a limit on storage. Additionally, the Charge 6 introduces the capability to broadcast heart rate via Bluetooth to select third-party apps, such as Peloton.
Integration with Google: Fitbit is fully integrating into the Google ecosystem, a development that followed Google’s acquisition of Fitbit in 2021. The Charge 6 includes features like Google Maps, Google Wallet, and YouTube Music (subscription required). However, it’s essential to have a Google account to use the Charge 6, even if you already have a Fitbit account (you can still track workouts via the Fitbit app).
Connection Issues: Despite the built-in GPS advantage, the Charge 6’s GPS performance could benefit from enhancements. We encountered some connection issues that were not present during our tests with dedicated GPS running watches. Some testers have also reported experiencing inconsistent GPS connections and frequent disconnections, indicating there’s still room for improvement in this area.
With a bigger screen than the Inspire 3, the Charge 6 can show more data, such as battery life, date, step count, distance, and Fitbit’s personalized energy zone metric.
Also great: Apple Watch SE
Apple Watch SE (2nd generation)
A smartwatch and fitness tracker in one
The Apple Watch SE delivers some of the most precise readouts and—with a mobile plan—can be used for calls and messaging. But its battery life is much shorter than that of our Fitbit picks.
If you’re already immersed in the Apple ecosystem, the second-generation Apple Watch SE stands out as our budget smartwatch pick for iPhone users. It’s a reliable choice for tracking essential metrics like step counts, distance traveled, and heart rate. While there are workarounds to use an Apple Watch with an Android phone, the pairing isn’t straightforward, making it far more advantageous for those who are fully integrated into Apple’s ecosystem. This smartwatch seamlessly complements your iPhone, providing a cohesive user experience and access to a wide range of health and fitness features.
All of the Apple Watch’s apps are featured in a bubble layout, accessible by pressing the right dial on the side of the screen.
The Apple Watch SE boasts a top-notch display and design. Its vibrant screen is fully customizable in the Watch app, allowing you to add shortcuts for features like weather reports or connect to apps such as Nike Run Club. The comfortable rubber band is also the easiest to put on among the trackers we tested; simply select the peg that fits your wrist size and tuck the remainder of the band underneath a slit. Dr. Mary Delahoussaye, director of Split Second Cares, emphasized that an elastic or Velcro band should be a standard accessory for Apple Watches, particularly for individuals who may struggle with the multistep process. While Apple offers a variety of options for universally designed bands, some of the more inclusive designs can be pricier or not available for the SE model.
The Apple Watch SE tracks several unique metrics, some of which are more useful than others. Like all Apple Watches, it encourages you to close a trio of rings—red for “Move,” green for “Exercise,” and blue for “Stand”—each day. However, these rings are not always the most meaningful indicators of personal health feedback; they often serve more as a daily competition. Notably, the Apple Watch also includes a wheelchair mode, which tracks pushes instead of steps, making it a versatile option for a wider range of users.
The Apple Watch SE syncs easily with Apple’s Health app to provide visually clear data.
See Apple’s privacy policy.
It has lots of add-on modes but does the simple stuff well, too. There are dozens of workout modes to choose from—more than Fitbits offer, including activities like Tai Chi and pickleball—so you can really get specific. We found that the watch trailed the Fitbit Inspire 3 only when it came to measuring step counts accurately. The SE also performed solidly in our distance testing.
The battery life is very short. The SE doesn’t have an always-on display, and it has a mere 18 hours of projected battery life, falling far below that of most designated fitness trackers. In a test, we found that the battery had dropped to 9% after 18 hours of use, so if you’re traveling overnight, be sure to bring a charger.
The Apple Watch SE is covered by a one-year warranty.
Other good fitness trackers
The Whoop 4.0 has no display, and all data is stored through its app.
If you’re a serious athlete who doesn’t care about tracking steps: You may like the Whoop 4.0, a niche tracker that uses a subscription model ($30 a month/$239 annually). It’s a good tracker for people seeking specialized health feedback or data on every workout, movement, and resting period they complete. The band, made of poly Lycra and pima cotton, is comfortable to wear, and the tracker sends information to an app where your workouts and recorded health information lives. A coaching feature suggests how much recovery is needed after a workout and provides insight on how hard certain muscles work during training. You can track recovery trends, and monitor respiratory rate, SpO2 (blood-oxygen levels) and temperature.
The Amazfit Band 7 is an accurate budget tracker.
If you’re looking for a budget tracker, the Amazfit Band 7 is an excellent option, offering fairly accurate readouts along with impressive battery life. Advertised to last up to 18 days, our tests revealed that after two days of continuous use, it still had 90% battery remaining. Aesthetically, the Amazfit Band 7 closely resembles the Mi Xiaomi Smart Band 7; a representative from Amazfit noted that the company shared manufacturing resources with Xiaomi until late 2022. In our tracking and distance tests, the Amazfit Band 7 outperformed the Mi Xiaomi Smart Band 7, although it still fell short of the capabilities of our top pick. This combination of affordability and performance makes the Amazfit Band 7 a strong contender in the budget fitness tracker category.
The competition
Over the past eight years, we’ve tested 45 wrist-worn wearables, including the discontinued predecessors of many devices reviewed here. In early 2023, we evaluated just before the company announced its decision to discontinue support for the Halo series on July 31, 2023. As a result, the devices and app are no longer functional. walmart has stated that it will refund any unused and prepaid Halo subscription fees and assist owners in recycling their Halos at no cost. This commitment to customer service reflects the company’s acknowledgment of the limitations of the Halo series, emphasizing the importance of long-term support in the wearables market.
In 2023, alongside the Mi Smart Band 7, we also tested the Garmin Venu Sq 2 and Garmin Vívomove Sport. While both devices underperformed in our step count tests, they offer notable perks, including accurate heart-rate readouts and seamless integration with the user-friendly Garmin app. Both Garmins could easily qualify as smartwatches—the Vívomove Sport, in particular, is designed to resemble a fashionable accessory—making them ideal choices for those who prioritize style over substance. This blend of aesthetics and functionality positions the Garmin devices as versatile options in the fitness tracker and smartwatch landscape.
The Fitbit Luxe has a slim, jewelry-like profile, with optional accessories that feel more like bracelets and less like sporty bands. We had a few hiccups, like when the Luxe blacked out during heart-rate testing and we couldn’t get back to the display.
If you want to keep in-depth records of your workouts, the Garmin Vívoactive 4S is a sporty, advanced fitness tracker with an emphasis on exercise. Its color touchscreen is clear and responsive, albeit more muted than those of a few color-screen competitors. Buttons beside the screen make it easier to toggle between workout modes or to start and stop workouts, and workout-data screens display more than one metric simultaneously.
The best thing the Garmin Vívofit 4, a former pick for basic fitness tracking, has going for it is that you don’t need to charge it, since it runs on a watch battery that’s good for a year. It also looks dated.
Instead of using step counts as the primary stat, the Mio Slice claims to measure all-around activity with a proprietary “personal activity intelligence” based on heart-rate monitoring.
The third-generation Oura Ring did not track our tester’s workouts as well as the wrist-worn devices she tested alongside it.
The Polar Unite has the sporty look of a fitness watch, and it can hold up to 20 sport profiles. We had a hard time getting it to connect to our phone for GPS use. It was comfortable—its heart-rate sensor is flat, which is a nice touch.
We’re fans of the minimalist aesthetic of the Withings Pulse HR; a reinforced polycarbonate surface coating over the screen has a cool, matte finish. The company, perhaps best known for its smart scales, has built in a seemingly impossibly long battery life—20 days—which held up in our testing. Step counts were hit or miss, sometimes nearly spot-on and other times far off. And it didn’t perform as well in our active-heart-rate tests as we expected.
Sources
- Andrew Jagim, PhD, director of sports medicine research at the Mayo Clinic Health System, phone interview, September 9, 2021
- Seth Martin, professor of Medicine in the Division of Cardiology at Johns Hopkins Hospital, email interview, January 17, 2023
- Max Paquette, associate professor in the College of Health Sciences at the University of Memphis, phone interview, January 19, 2023
- Nicole Hagobian, running coach, sport and exercise scientist at California Polytechnic State University, email interview, January 30, 2023
- Meagan Wasfy, sports cardiologist at Mass General Brigham, email interview, February 6, 2023
- Dr. Mary Delahoussaye, director of Split Second Cares, email interview, March 3, 2023
- Aric A. Prather, PhD, professor of psychiatry, University of California, San Francisco Weill Institute for Neurosciences, email interview, May 10, 2023