I ride a recumbent bike, and I always do an hour and 10 minutes. I am 35 and I know my max HR should be about 185. However, tonight for instance my avg. was 153 bpm and max was 176 bpm. I've been riding for several months though, so I didn't just start up at this level. Anyway... just wanted to know what was safe. I just sort of figure my heart should be in the best condition it can be in case I even need to push it beyond the typical 75-80%.

On a side note... why do I smell like ammonia when i'm riding?