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Getting Started 5
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Athlete App 3
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Teams Solution 2
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Sensors, Kits, and Packs 3
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Accounts and Orders 2
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Data and Education 8
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Troubleshooting 2
Understanding Heat Strain
The Heat Strain Index helps you understand how your body is responding to heat and effort in real time—so you can adjust before performance drops.
What Is the Heat Strain Index?
The Heat Strain Index is a real-time score from 0 to 10 that shows how hard your body is working to regulate temperature during exertion. It combines data from core body temperature, skin temperature, and heart rate—captured through your HeatSense thermal sensor and HRM—to give you a single performance-relevant metric.
Why It Matters
As you train or compete, your body works to cool itself through sweat and blood flow. But in high heat or during prolonged intensity, these systems can become overloaded—leading to rising core temp, accelerated heart rate, and reduced power output. That’s heat strain—and understanding it is the key to managing performance under pressure.
More Than Core Temp Alone
Core body temperature is important—but it doesn’t tell the whole story. The HeatSense algorithm calculates mean body temperature by blending core and skin data to reflect total heat load more accurately. This holistic view is what drives the Heat Strain Index score.
How to Read the Score
| Index Score | What It Means |
|---|---|
| 0 – 0.9 | No Heat Strain Your body is regulating well. Core temperature may be slightly elevated from exercise, but skin temperature is neutral — meaning heat is dissipating normally. This is your performance zone. You can push, recover, and train effectively. |
| 1-2.9 | Moderate Heat Strain Both core and skin temperatures are rising. Your heart rate may be slightly higher than usual as your body works harder to cool itself. You might feel warm. Performance may start to dip — not dramatically, but it's happening. This is a signal to stay aware. |
| 3–6.9 | High Heat Strain Your body is under significant thermal load. Core and skin temperatures are elevated. You're sweating heavily and blood is being redirected to the skin to help cool you down — which means less oxygen is getting to your muscles. Your heart is working harder to compensate. You'll feel hotter, your heart rate will climb, and motivation often drops. Performance and endurance are noticeably reduced. Exhaustion comes faster. |
| > 7 | Extremely High Heat Strain Prolonged activity here puts you at risk for heat-related illness. Warning signs include muscle cramps, dizziness, nausea, headache, or collapse. Performance drops drastically. You may need to stop entirely. Listen to your body — and if you see these signs in someone else, act quickly. |
How to Train With It
- Game Day Strategy: Stay in lower strain zones to protect performance late in competition.
- Acclimatization: Intentionally expose athletes to higher strain (45–80 min) during training blocks to build heat readiness—always under controlled monitoring.
- Recovery Optimization: Use the Index post-session to evaluate cooling effectiveness and session load.
Your Heat Strain Index is visible in real time through the HeatSense app.
