Originally Posted by
siovene
I'm actually surprised at how fast I was for such a low heart rate. I'd never tried before. It seems that if I just want to average 1 or 2 km/h faster, it's going to cost a lot in terms of heart rate. Is that really the way of it?
Yes. Wind resistance increases as the cube of the speed. Wind resistance consumes a large portion of your power.
Also, average speed is not a good way to measure your performance. Too many thing affect it even on the same course... wind being the major factor.
While LTHR does increase with training, it is slow to change and won't change a lot.