How I Improved My Fitness Performance by Tracking This Often-overlooked Metric

Matthew Miller/ZDNET

Key insights from ZDNET

  • The core body sensor is available now for $285.
  • It provides an accurate measurement of internal body temperature, is lightweight, has a long battery life, and is a functional smartphone app.
  • The device is quite expensive and must be connected to a chest strap or an adhesive patch.

Wearable technology has evolved significantly over the last decade and amateur athletes can now collect extensive amounts of data with their smartwatches, GPS sports watches and external heart rate monitors. I’ve been running and cycling with it for the last few months Core sensor<!–>a wearable device that detects and records your internal body temperature without the need for other invasive methods.

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Historically, heart rate measurement has been the most common metric for tracking runners’ performance, but in recent years more attention has turned to running performance. Almost every new GPS sports watch and smartwatch now tracks and calculates mileage to normalize the unevenness of the terrain you exercise on and the physical effort you exert.

View at Core–>

The Core Body Temperature Sensor adds another element to your training program, and while it may be more important for professional athletes, its price is so high that even amateur athletes get access to its insights. When I first tested it in the Pacific Northwest in January, the outside temperatures were too cold for me to sense a noticeable increase in my internal body temperature.

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However, after taking a trip to visit my daughter and future son-in-law in Australia, I saw firsthand the value of the Core’s metrics. I completed three long runs in my first week in temperatures only experienced in mid-summer in Washington state, and was surprised to find my core temperature and heat stress index readings rising to a level where the device indicated my performance was beginning to suffer .

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Matthew Miller/ZDNET

My recent 20 pound weight loss has significantly increased my running pace and given Brisbane’s mostly flat landscape I was able to keep up with my pace easily. However, after 35 to 40 minutes, my pace slowed while my sweat output increased. I slowed down a bit and saw my internal temperature drop as well.


Australia is much wetter and hotter than Washington State, but as I’ve gotten older my tolerance for humidity has increased, so I’ve felt quite comfortable running in the humid conditions. When running in Washington, my skin temperature feels pretty cold, even after a long run with a lot of sweat. In contrast, my skin temperature remained much more constant in Australia.

This points to one of the main applications of the core body sensor used by athletes: determining optimal cooling strategies during hard training sessions. Core’s website shares experiences with cyclists seeing up to an 8% increase in speed after just 10 days of heat-focused training. Unfortunately, I didn’t train with the Core long enough to develop a training strategy with it, but I was able to collect enough data to see the potential benefits of training with the sensor.

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Matthew Miller/ZDNET

One of the easiest ways to attach the Core to measure your temperature is to attach it to a heart rate chest strap. When running, it was connected to the strap of my Garmin HRM-Pro Plus. The clip holds the core in place very well, but you can also attach the core sensor directly to the body using the disposable sports adhesive plasters provided.

To power the device, the core sensor is charged via the USB-A cable using its proprietary magnetic cable. Core claims six days of continuous use on a full charge, and in my eight workouts with the device, I only charged it once to ensure it was ready for any longer runs.

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The Core measures your skin temperature and then uses its proprietary algorithms to calculate your internal body temperature. Tests have confirmed the accuracy of the Core Sensor, so there is no need to use an internal probe or e-pill to measure your internal temperature. Since I haven’t used a rectal probe since I was a child, it was interesting to see the measurements of my internal temperature.

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Matthew Miller/ZDNET

While there is a Core smartphone application that collects and displays all of your measurement data, you can also connect the Core sensor to your Garmin, Coros, Suunto, Apple Watch and other recent wearables. I used it primarily with a Garmin Quatix 7 Pro and a Coros Apex 2 Pro. So it was great to have the core data appear as a separate field while running and then on the summary data pages in the associated smartphone applications.

The highest body temperature I recorded during my five training sessions in Washington was 100.9 degrees. In Australia, I experienced a high of 102.5 degrees on my last of three runs. This run was just over seven miles long and ended around 10am, so the temperature outside was rising.

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My heat stress index also rose to 4.12 during this run and it was clear that I needed to slow down and lower my internal temperature if I ran longer. Knowing these heat load and training load metrics provided by the device can go a long way in optimizing a training program and providing insight into your body’s physical limits.

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Matthew Miller/ZDNET

If you are considering the Core Body Sensor for a better workout, I highly recommend that you read through the manual and FAQs on the website. There are also testimonials from athletes that can help you figure out if the $285 sensor is worth it to better understand your body and how it responds to the environment and your training program. Core states that indoor temperatures above 102 degrees Fahrenheit put the human body at risk for heat stress.

ZDNET’s buying guide

While I could train for my simple recreational races and activities without the use of wearable technology, I find it fascinating to collect the data and then create reports. The core body sensor–> adds another metric to the mix and if I lived in regions like Australia or the southern US I would consider adding the sensor to my arsenal. It’s fascinating to see how accurate the core sensor is and how cost-effective it is to use than advanced body temperature methods traditionally used by high performance athletes.

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