I'm not actually outside yet, I use the RPM bikes provided in the classes so there is no shifting, only adjusting the resistance. I am only basing my heartrate on what I have experienced in different training situations, I know it is not very scientific but I can tell when it is pounding in my throat and it is really racing vs. a raised, but not max target rate. I agree, if I'm out of breath that should be the max but my legs are worn out before that point where you are gasping for air and the only reason I am trying to get to that point is that I'm trying to get as in shape as I can! I have about 20 pounds to lose and I have to "learn" how to bike the best that I can for this trek