HR is activity dependent. HR targets will be different whether you are biking, running or swimming. that is why it is really important to use RPE (rate of perceived exertion) AND HR together. HR equations are also inaccurate (although some are better than others).

When you are on your bike, your heart works a little differently to pump blood through working muscles than when you are standing (like running) or laying (like swimming). Even recumbent HR targets will be different since laying with legs in front means blood doesn't have to work against gravity to get to the legs.

There are various scales for RPE, 6-20, 1-10...basically giving a value to how you feel (1 is easy, 5 moderate 10 cannot continue and fill in in between).

Chin up!

han