Often we hear cyclist frustrated by the difference in power numbers they produce relative to heart rate when riding indoors as opposed to out on the road. We can do an example with a cyclist, a masters racer… 45 years old, been cycling for the last 6 years. Whenever he conducts a FTP test outside he is posting better 20 minute numbers vs a test on a trainer. The HR of the data is the same. We have tried a multitude of things to improve his “trainer” FTP (to match his outside FTP), such as fans, using the trainer outside, music…. but there still seems to be a difference.
Here are the numbers from a past test: on a trainer resulting in 258W and an average HR of 174. He was frustrated at his low number so 10 minutes later he went outside and put down a 278W with 175 HR.
A lot of riders experience this. But we’ve also heard from some who have exactly the opposite problem—better numbers indoors than out. So it remains a mystery. There are a couple of possibilities that may explain it, but they are rather lame we’ll have to admit. One is that when riding on the road there are brief episodes of “recovery” due to slight hills, cornering and changes in wind direction. These little changes don’t occur indoors on a trainer where power is usually much steadier. Some research shows that these little “mini-recoveries” allow the rider to go harder overall.
The next is that when riding on the road the bike actually rocks from side to side slightly while the body remains relatively steady over it. On the trainer it’s the opposite – the bike is locked in place so the rider’s body moves slightly side to side while pedaling. This requires a somewhat different technique and muscle recruitmen and so may elevate HR and effort “artificially.”
Could one of these explain a 7% difference? Probably not. Could some combination of them account for that? Possibly. Bottom line is that I really don’t know.