What velocity said is absolutely correct.A case in point is, this week I am doing night duty,so pretty much don't get as much sleep as I would have liked.And these few days my heart rate during the ride is where my work load should be at around 70-80% but yet I am only pedalling at around 50-60% effort.If I have to stick to what my HRM tells me for my recovery ride for the week ( I try to do recovery ride during the night duty week so to keep up my fitness and without putting too much strain on my body,but that is another story ),then I would have to soft pedal so softly that I may as well have the day off the bike

So the bottom line is listen to your body and the HRM is only a guide afterall.

In regards to the different heartrate for different sport is due to the working musles are used in different way,and from what I have learned,those sport that used the lower body part such as our feet,the heart has to pump much harder to supply the nesseccary blood flow and that will have a much higher heartrate than sport that using the upper body such as swimming which is using our hands as primary musles.