Sometime in September of 2010 I started training for the 2011 race. I managed to shave 30 seconds off of my 2009 time with only a few months of training and decided to push it even harder for the 2012 race. I also picked up a heart rate monitor a few months ago in order to get a more detailed understanding of how my body was responding.
As your aerobic capacity increases, your heart gets physically bigger and is able to pump more blood during every cycle. This causes your RHR (Resting Heart Rate) to slow down, which is a good way to track your progress. I got my heart rate monitor on 17Aug2011 and strapped it on for the night while I was sleeping. I added a daily run to my training and strapped on the monitor again last night (05Oct2011) to check my progress.
The results speak for themselves - the blue graph is my August data and the pink represents the current state of affairs.
(Click to embiggen...)
From a subjective standpoint, I feel a lot calmer and more relaxed. The little things do not bug me as much as they used to, and on nights where I cannot get in enough sleep, I feel perfectly fine the next day.
To be sure, the data is not perfect (you are not perfectly at rest while sleeping) and last night could have been an anomaly. I will continue to track this on a monthly basis and see if a true trend is developing. I like what I see so far though.