Originally Posted by Trek Rider
A max heart rate doesn't decrease as you get more physically fit. As you excercise and increase your level of fitness, your cardio-vascular system also becomes more efficient. What this means is that it takes your heart less work to get oxygen to where it's needed in your body, which means you have a lower heart rate for the same level of effort.
HRmax *DOES* decrease with increased fitness level, and is mainly related to changes in plasma volume (which increases). for e.g., see
http://www.ncbi.nlm.nih.gov/entrez/q...t_uids=3747802
this shows HRmax (termed peak in this study, but the same thing) increases on average 9 b/min after detraining.
ric