Comparison

CORE Thermal Sensor vs Fuelin

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

Head to head
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.

About

Fuelin

This app provides personalized sports nutrition plans for athletes, adapting daily calorie and macro targets to workouts and goals. It offers smart meal recommendations, workout fueling guidance, and body composition management. Log food easily via voice, text, or barcode scanning.

Highlights
  • Personalized daily nutrition targets
  • Workout and race fueling guidance
  • Smart meal and portion recommendations
  • AI-powered food logging
  • Body composition management
  • Workout integration with popular platforms
  • Hydration and gut training tools
Features
Read full description

Fuelin is a personalized sports nutrition and fueling app for runners, cyclists, triathletes, hybrid athletes, and anyone who trains. It tells you what, when, and how much to eat: your daily calorie, carbohydrate, protein, and fat targets adapt to your workouts and goals, so you can fuel training, recover well, and manage body composition. Fully automated, no math required. Fuelin is trusted by 100K+ athletes. WHO IT'S FOR Whether your goal is everyday fitness, weight loss, muscle gain, HYROX, a marathon, or IRONMAN, Fuelin plans your nutrition. Supports 30+ sports and activities, from swimming to CrossFit. NUTRITION THAT ADAPTS TO YOUR TRAINING • Daily nutrition planning: calorie and macro targets adapt to planned and completed workouts, so hard days get more fuel and rest days less. • Smart Meals: personalized meal and portion recommendations based on your goals, training, and preferences. • Smart Adjustments: upcoming meal targets rebalance based on what you've already eaten. • Workout and race fueling: guidance on what to eat and drink before, during, and after runs, rides, and hard sessions, plus Race Week coach insights. • Body composition: lose weight or build muscle while still fueling your workouts. • Simple food logging: talk or type to the AI food logger, scan a barcode, save recipes and meals, and log in units like scoops or slices. PERSONALIZED TO YOU Fuelin builds your plan around your goal, body weight, gender, athlete experience level, and daily activity level. It estimates your resting metabolic rate (RMR), functional threshold power (FTP), and threshold pace, or you can enter your own. BUILT WITH SPORTS NUTRITION EXPERTS Created by sports dietitians, including co-founder Scott Tindal (20+ years in pro sport) and Dr. Alan McCubbin (researcher, 20 years with endurance athletes). IRONMAN World Champions Jan Frodeno and Daniela Ryf are on the team. WORKOUT INTEGRATIONS Connect Garmin, Strava, TrainingPeaks, V.O2, Pushing Limits, Final Surge, HumanGO, TriDot, or RunDot. You can also add workouts manually. HYDRATION, GUT TRAINING & MORE • Sweat Rate Tracker: measure sweat rate to guide hydration. • Carb Capacity Testing: gut training for endurance exercise. • In-app lessons on portions, supplements, and energy balance. • Community chat with Fuelin athletes. • Fuel Shop: member perks from Maurten, Momentous, and other partners. COMMON QUESTIONS How is Fuelin different from a calorie tracker? Calorie trackers count what you eat against a target. Fuelin sets that target from your workouts and goals, recommends meals and portions, and rebalances upcoming meal targets around what you've eaten. Do I need to be training for a race? No. Fuelin supports everyday training and rest days, whether your goal is more energy, weight loss, muscle gain, or an event. Can I use MyFitnessPal or Lose It!? Nutrition data from MyFitnessPal or Lose It! can sync to Fuelin through Apple Health. Does Fuelin include a human coach? Autopilot, Fuelin's core plan, is fully automated and doesn't include a coach. Copilot adds 1:1 messaging with a Fuelin nutrition coach and live group coaching every two weeks. WHAT ATHLETES SAY "Fuelin is the daily companion to take the guess work out of nutrition that I wish I had earlier in my career." - Jan Frodeno, 3x IRONMAN World Champion PLANS Fuelin requires a paid subscription. Autopilot: automated nutrition planning, Smart Meals, Smart Adjustments, food logging, workout syncing, hydration and gut-training tools, lessons, and community chat. Copilot: everything in Autopilot plus 1:1 coach messaging and live group coaching every two weeks. Medical Disclaimer: Seek a doctor's advice in addition to using this app and before making any medical decisions. Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/ U.S. Barcode Food Database Powered by FatSecret: https://fatsecret.com International Barcode Food Database Powered by Open Food Facts: https://openfoodfacts.org

Screenshots

CORE Thermal Sensor4 screens
Fuelin4 screens

Verdict

The call

The clearest difference is rating: Fuelin at 4.5 against CORE Thermal Sensor's 2.5. Fuelin also leads on review sentiment (51% vs 19%) and update cadence (every 10 days vs every 2 months). CORE Thermal Sensor's advantage is in-app purchases (none vs 5) and ads (none vs shown). On price and iOS requirement 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. Fuelin sells 5 in-app purchases, starting at $29.00 per month. CORE Thermal Sensor asks for nothing beyond the download.

ReceptionRating · Positive reviews · Number of ratings

Fuelin holds the better App Store score, 4.5 against 2.5. That said, the two scores are not equally well evidenced: Fuelin has 1.3K ratings behind it against 35, so its average is the more settled of the two. Written reviews point the same way: 19% of CORE Thermal Sensor's written reviews are positive against 51% of Fuelin's.

UpkeepUpdate frequency

CORE Thermal Sensor ships an update every 2 months, Fuelin every 10 days. The most recent releases landed on November 3, 2026 and November 7, 2026 respectively.

Scorecard8 real differences · 2 level
CORE Thermal Sensor versus Fuelin: the parameters behind the verdict, then further details
ParameterCORE Thermal SensorFuelin
PriceFreeFree
Rating2.5 (35 ratings)4.5 (1.3K ratings) — better
Positive reviews18.8% of reviews50.5% of reviews — better
Number of ratings351.3K — better
Update frequencyEvery 2 monthsEvery 10 days — better
AdsNo — betterYes
In-app purchasesNo — betterYes
MonetizationFree — betterFree with in-app purchases
DevicesiPhone, iPad, iPod — betteriPhone
Requires iOS15.1 — better16.4
Further details — not scored
Size55 MB87 MB
Age rating4+17+
Developergreenteg AGThrive AI Labs

Customer experience

CORE Thermal Sensor

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

Fuelin

All ratings1,321 ratings
Positive86.8%
Neutral3.0%
Negative10.2%
Written reviews299 reviews
Positive50.5%
Neutral11.7%
Negative37.8%

In-app purchases

None

CORE Thermal Sensor

No in-app purchases

5 purchases

Fuelin

Subscriptions5
  • Autopilot Monthly Plan$29.001 Month
  • Copilot Monthly$99.001 Month
  • Autopilot Yearly Plan$139.001 Year
Show 2 more
  • Autopilot Yearly7 Days trial$139.001 Year
  • Copilot Yearly$399.001 Year

Questions

Is CORE Thermal Sensor free?
CORE Thermal Sensor is free to download, with no in-app purchases.
Is Fuelin free?
Fuelin is free to download, with in-app purchases available.
Which has better reviews, CORE Thermal Sensor or Fuelin?
Fuelin is rated higher. CORE Thermal Sensor averages 2.5 out of 5 from 35 ratings, while Fuelin averages 4.5 from 1.3K ratings.
Do CORE Thermal Sensor or Fuelin have ads?
Fuelin shows ads; CORE Thermal Sensor does not.
Which is updated more often, CORE Thermal Sensor or Fuelin?
CORE Thermal Sensor ships an update every 2 months, and Fuelin every 10 days. Most recently, CORE Thermal Sensor was updated on November 3, 2026 and Fuelin on November 7, 2026.

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