Core body temperature is the hidden variable in cycling performance—and now it's measurable. Ross McRa from Core walks us through why thermal power matters as much as mechanical power, how heat training creates adaptations similar to altitude camps, and how top teams like Remco's are using continuous core temp monitoring to gain a competitive edge.
Key Takeaways
- Power output drops roughly 5% for every 1°C increase in core body temperature, making thermal efficiency as critical as mechanical power in races.
- Heat training in Zone 3 (your optimal heat adaptation zone) is paradoxical: it builds vascular and hemoglobin adaptations during training but signals you need to cool down during racing to maintain performance.
- Core temperature can be measured non-invasively using heat flux sensors (mimicking skin's energy transfer) combined with skin temp and heart rate—avoiding the need for rectal probes or expensive telemetry pills.
- Heat adaptations take roughly 2-3 weeks at high frequency (6 sessions/week) or 12 weeks at lower frequency (2-3 sessions/week), and once adapted, you only need 1-2 maintenance sessions weekly to retain the benefit.
- Kit and thermal properties matter as much as aerodynamics: optimized fabrics can provide 10-20% better thermal performance, a gain comparable to marginal aero improvements teams obsess over.
- Heat training is an extra stressor—adding it without coach oversight and adjusting total training load will throw off your entire plan and recovery.
Expert Quotes
"The human body is similar to just any other thermal engine—we understand pretty well power in pedals, the mechanical power that's 20%, but the human body being rather inefficient means that another 80% needs to be dissipated through heat, and we've had very little understanding of that thermal power."
"If you're doing the same session, what you'll start to see is your core temp will be lower at the same power threshold—that's an easy way to look at it. You're being more efficient; your thermal power is lower to hit the same mechanical power number."
"Once you've adapted you've adapted, and then you can go into maintenance mode and focus maybe on other ways to optimize your performance. The maintenance is lower stress so maybe before your event you can back off and recover a little bit but maintain the benefit."