When watts become heat
In cycling, watts usually mean one thing: the power a rider puts into the pedals.
But the body is not a perfectly efficient engine. A relatively small part of the energy becomes mechanical power that moves the bike forward. A much larger part becomes heat inside the body.
“For every calorie the human body burns, roughly 20 percent becomes mechanical watts, creating forward motion. Around 80 percent goes to other processes — especially heat,” Bu explains.
For elite athletes pushing 300 to 400 watts on the bike, that can mean producing 1500 to 2000 watts of heat. In simple terms: almost like having a heater on full power inside the body.
That is the heat CORE helps make visible. The sensor estimates core body temperature indirectly by combining skin temperature with heat flux — a measure of how much heat is moving from the body towards the skin and out to the environment.
“CORE measures heat flux, or thermal watts, together with the temperature of the skin. When you combine those two, you can estimate the body’s core temperature quite accurately,” Bu says.
If the rider cannot get rid of heat efficiently, performance starts to drop. Heart rate rises, the effort feels harder, and the body may eventually force the rider to reduce the power on the bike.