Comparison

Retül Fit vs CORE Thermal Sensor

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

Retül Fit

This app uses advanced technology to collect and analyze rider data, helping retailers and fitters improve comfort, prevent injuries, and enhance performance. It leverages insights from professional athletes to benefit riders of all levels.

Highlights
  • Rider data collection and analysis
  • Injury prevention guidance
  • Performance improvement insights
  • Product decision support
  • Professional athlete insights
  • Modern immersive experience
Features
Read full description

Retül is an inspirational, immersive and modern experience for riders. Our technology is used to collect and analyze data to help retailers and fitters advise riders and help them make the best product decisions to increase comfort, prevent injuries and improve performance. We've been partnering with Specialized since 2012. Together, we've been able to take Retül technology to new heights, and along the way, we've also elevated the precision of Specialized's Body Geometry products. This relationship has also brought a tremendous opportunity to Retül, as we've been fully integrated with Specialized's pro-level athletes and teams. Now, we can take what we've learned from working with the world's most demanding riders and apply this knowledge directly to riders of all experience levels and motivations. Based in Boulder, Colorado, we've specialized in bike fitting technology and training since 2007. In that time, we have performed thousands of fits and taught hundreds of training courses around the world. We have helped bike shops, fit studios, performance centers and medical professionals implement Retül technology services into their businesses. Here, we've also been able to work with the most talented team in the industry, employing everything from software development to shipping & receiving. And now, we're situated in a brand new Innovation Center here in Boulder, which allows us to both grow and expand upon exciting new projects and groundbreaking innovations.

About

CORE Thermal Sensor

This app continuously monitors your core body temperature and thermal strain, providing critical data for heat training and optimal race performance. It helps athletes of all levels improve their training and achieve better results.

Highlights
  • Continuous core body temperature monitoring
  • Real-time Heat Strain Index
  • Heat Zones for training and racing
  • Heat Training Load and Adaptation Score
  • Passive heat training tracking
  • Data trends and historical analysis
  • Connectivity with sports devices
Features
Read full description

The CORE Thermal Sensor accurately measures your core body temperature and thermal strain on your body – continuously and non-invasively. Thermal data and insights are critical for facilitating safe and effective heat training and for performing optimally on race day. Designed for athletes at all levels, CORE will help to improve your training and performance in your personal adventures or races. IMPORTANT: The CORE app is designed to work with the CORE device which you can order at www.corebodytemp.com Here's how it works: • Set up your CORE sensor: connect your heart rate monitor and sports devices for optimal sensor use. • Measure your thermal vitals during training: mount the newly designed clip on your heart rate strap and snap in the CORE sensor. Shake the sensor to wake it up, wear it and track your thermal data. • Core body temperature: the interior temperature deep in your body, including organs and other tissues. A critical measure during sports, it can reach up to 40°C (104°F) during vigorous activity in hot environments. Be aware that hotter is not better – cooler is faster. • Heat Strain Index: A combination of your core body temperature and skin temperature representing the thermal strain on your body. The real-time feedback on how hard your body is working to stay cool, delivering a value from 0 (no heat strain) to around 10 (extremely high heat strain). • Heat Zones: Your Heat Strain Index divided into easy-to-use zones. Heat Zone 3 will likely lead to a performance loss, BUT it is the needed stimuli to create adaptations in your body. During heat training, strive for time in heat zone 3. During racing, stay cool and prevent a performance loss by staying in heat zone 1 or 2. • Heat Training Load: a cumulative daily metric of the heat strain on your body. A daily value of 10 out of 10 indicates ideal contribution to heat adaptations. More is not always better! • Heat Adaptation Score: Track your heat adaptations over time with effective heat training. Get a heat champion to perform best in the heat. Long-term heat training will most likely lead to improvements also in cool conditions. • Add your passive heat training: Supplementing your active heat training or general training with passive heat exposure in a sauna or hot bath. You can track your sessions in the app manually, contributing to your heat adaptation score. NOTE: do NOT take your CORE sensor into the sauna or hot environments. What else you can do in the CORE app: • Dig into the details: See a breakdown of your thermal data, and even see trends across days, weeks and months. • Share your CORE metrics with your friends through the social sharing feature, earning more kudos and likes • Connect your connectivity accounts (e.g. Garmin) to directly synchronize your data after the training. • Update your sensor to the latest firmware ensuring having the best sensor functionality. Note: CORE provides products and services designed for general fitness and training purposes. For accurate measurement readings during sports, a connection to a heart rate monitor is necessary. CORE products and services are not medical devices, not intended to treat or diagnose any disease, and should not be used as a substitute for professional medical advice, diagnosis or treatment. All content available through CORE products and services is for general informational purposes only.

Screenshots

CORE Thermal Sensor4 screens

Verdict

The call

The clearest difference is monetization model: CORE Thermal Sensor at free against Retül Fit's free with in-app purchases. CORE Thermal Sensor also leads on review sentiment (19% vs 0%) and ratings volume (35 vs 5). Retül Fit's advantage is update cadence (fortnightly vs every 2 months). On price, rating, ads and in-app purchases there is nothing between them.

Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS

CostPrice · In-app purchases · Ads · Monetization

Both are free to download. Neither carries in-app purchases, so what you see is what you pay.

ReceptionRating · Positive reviews · Number of ratings

On the App Store both sit at effectively the same score — 2.6 for Retül Fit against 2.5 for CORE Thermal Sensor. That said, the two scores are not equally well evidenced: CORE Thermal Sensor has 35 ratings behind it against 5, so its average is the more settled of the two. Written reviews are what separate them: 0% of Retül Fit's written reviews are positive against 19% of CORE Thermal Sensor's.

UpkeepUpdate frequency

Retül Fit ships an update fortnightly, CORE Thermal Sensor every 2 months. The most recent releases landed on October 11, 2026 and October 15, 2026 respectively.

Scorecard5 real differences · 5 level
Retül Fit versus CORE Thermal Sensor: the parameters behind the verdict, then further details
ParameterRetül FitCORE Thermal Sensor
PriceFreeFree
Rating2.6 (5 ratings) — better2.5 (35 ratings)
Positive reviews0.0% of reviews18.8% of reviews — better
Number of ratings535 — better
Update frequencyFortnightly — betterEvery 2 months
AdsNoNo
In-app purchasesNoNo
MonetizationFree with in-app purchasesFree — better
DevicesiPadiPhone, iPad, iPod — better
Requires iOS16.215.1 — better
Further details — not scored
Size181 MB55 MB
Age rating4+4+
DeveloperSpecialized Bicycle Components, Inc.greenteg AG

Customer experience

Retül Fit

All ratings5 ratings
Positive40.0%
Neutral0.0%
Negative60.0%
Written reviews4 reviews
Positive0.0%
Neutral25.0%
Negative75.0%

CORE Thermal Sensor

All ratings35 ratings
Positive22.9%
Neutral20.0%
Negative57.1%
Written reviews48 reviews
Positive18.8%
Neutral25.0%
Negative56.3%

In-app purchases

None

Retül Fit

No in-app purchases

None

CORE Thermal Sensor

No in-app purchases

Questions

Is Retül Fit free?
Retül Fit is free to download, with no in-app purchases.
Is CORE Thermal Sensor free?
CORE Thermal Sensor is free to download, with no in-app purchases.
Which has better reviews, Retül Fit or CORE Thermal Sensor?
Retül Fit is rated higher. Retül Fit averages 2.6 out of 5 from 5 ratings, while CORE Thermal Sensor averages 2.5 from 35 ratings.
Do Retül Fit or CORE Thermal Sensor have ads?
Neither Retül Fit nor CORE Thermal Sensor shows ads.
Which is updated more often, Retül Fit or CORE Thermal Sensor?
Retül Fit ships an update fortnightly, and CORE Thermal Sensor every 2 months. Most recently, Retül Fit was updated on October 11, 2026 and CORE Thermal Sensor on October 15, 2026.

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