I've been following the Carmichael Training System (CTS) for the last two years (extent of my cycling experience). As many of you may know, the CTS uses HR "zones" based on the average HR determined from a 3-mile "field test". Most of my winter riding is done indoors on a Computrainer. The problem I have is that when I do the field test indoors, my maxHR and my averHR are about 10 beats lower than when I conduct the field test outdoors on the road even though the perceived effort is the same (I want to puke in both cases). I max out at 176 indoors, and 186 outdoors (I'm 45 yo). What could be the reason for this? To check if there was a problem with my HR monitor, I wore my outdoor HR monitor while riding my computrainer, which has an integrated HR monitor, and the numbers matched up. My question is, should I be using two sets of averHR numbers as the basis for my training, one for outdoors and one for indoors, or should I just be using the higher of the two for all my training? I don't want to overtrain (by using too high a number indoors), but I don't want to undertrain either. Thanks for your input.