I am in really good shape. I go to the gym pretty much everyday. I usually lift 3 times a week and run the other 4. I have very little body fat. When I run I usually run for 3-4 miles averageing under an 8 min mile throughout the whole run. I have noticed that as I get in better and better shape my resting heart rate has gone down. its usually in the low 50s and when I'm relaxed before bed it can get down in the mid 40's. I have heard that guys like lance armstong have a resting pulse of 33, which is crazy, I dont think to many other people have it that low. Has anyone else noticed a pulse in the 40s and 50s when they were or are in good shape?

The better shape you are in the lower it can go, it is simply an indication of the strength of your heart. I read somewhere that the stronger it is, the more blood and oxygen it can pump with each beat, hence the fewer beats required per minute. I don't know if there is unhealthily low heart rate, but if your body wasn't getting enough oxygen and blood flow there would be indications that you were not healthy.

My heart rate is in the upper 40s to low 50s. I have been riding a bike for 25 years.