Heat Training with the CORE Sensor: Heat Zones Explained

What is heat training?

Heat training is the deliberate use of thermal load as a training stimulus. Instead of avoiding heat, you spend controlled time at an elevated core temperature — through warm rooms, reduced cooling, extra layers, or simply riding indoors where heat builds naturally. Done consistently over roughly two weeks, the body adapts in ways that improve performance not only in hot races but, according to a growing body of research, in temperate conditions too.

Why does heat training make you faster?

The best-documented adaptation is plasma volume expansion: more blood plasma means better stroke volume, cardiovascular stability and cooling capacity. Heat exposure also lowers your core temperature at a given workload, raises your sweat rate and starts sweating earlier — all of which delay heat-related fatigue. Research also points toward increases in haemoglobin mass with longer protocols, which is why heat training is increasingly discussed as a legal, practical complement to altitude training.

What is the CORE body temperature sensor?

CORE (by greenTEG) is a small wearable sensor, typically clipped to the heart-rate strap, that measures core body temperature continuously and non-invasively using thermal energy transfer technology. It transmits over Bluetooth, which means training apps can read your core temperature live during a ride — no ingestible pills, no lab equipment.

What are heat zones?

Heat zones translate core temperature into training ranges, exactly like power or heart-rate zones structure watts and pulse. The zone concept answers the key practical question of heat training: am I hot enough for an adaptation stimulus, or too hot to be productive? The adaptation sweet spot for most athletes sits around 38.3–38.8 °C. Below it, the thermal stimulus is minimal; far above it, performance and safety degrade. Live heat zones let you steer a session into the productive range and keep it there.

How do you structure an indoor heat session?

Indoor training is ideal for heat work because conditions are controllable. A proven starting pattern:

• Ride at an easy, steady endurance intensity — heat sessions are not interval sessions.
• Reduce cooling: fan off or low, moderate room temperature, optionally an extra layer.
• Use live core temperature to reach your target heat zone (~38.3–38.8 °C), then hold it for 30–45 minutes.
• Hydrate during and after; expect elevated heart rate at a given power — that is the stimulus, not a fitness loss.
• Repeat 4–6 sessions per week for about two weeks for the initial adaptation block, then maintain with 1–2 weekly sessions.

How does ENDURE integrate the CORE sensor?

ENDURE is the first indoor cycling app to natively integrate the CORE body temperature sensor — including a live heat-zone display right on the ride screen. Pair the sensor over Bluetooth like any power meter, watch your core temperature and current heat zone live while you ride, and find the full temperature trace stored with power and heart rate in your ride analysis afterwards. No second app, no workarounds — heat becomes a first-class training metric. Available in Early Release on iOS and Android.