I think everyone here knows that at a constant effort your HR will drift upwards overtime due to heat stress, dehydration, etc. In an attempt to measure my thermal cardiac drift I did a little heat stress experiment on my computrainer in ergometer mode. On consecutive days I did short submaximal workout that would be intense enough to bring on some heat stress, while still being short enough to rule out significant dehydration and heat illness. Yesterday I did the workout without a fan, today with a fan.
You can see that for the first 6.5min the HR data correlates beautifully ruling out calibration differences. This also indicates that at first, while you warm up to the new setting, the fan does nothing. However, after that the effect of the fan is dramatic; by the end of 5min at 300W the HR difference averages 6bpm (3% of 204MHR).
“It’s the same wattage who cares about HR?”
Sure, it’s all about the watts but if you overheat and blow up to much over 90% of max HR your internal thermostat will tell the central governor to decrease muscle fiber recruitment. In a race at the same wattage what condition would you rather be? Don’t ignore HR data; it should be able to tell us a huge amount. Why HR monitors won’t give us the derivative is beyond me, it could tell so much more….