I'm an avid 60 year old male cross-country skier, participate in a
few races, and have been training 375-425 annually with that in mind
during the rest of the year since the mid 1990s. My heart seems to be
in excellent shape, according to tests done during a June hospital
visit for chest pain during exercise, which turned out to be apparently
gastric reflux related. For example, on the standard Bruce test I
didn't have to start jogging until Stage 6 (they stopped me a minute
later to image the heart). But there is something else cardiovascular
related that I've wondered about.

In 1999 (age 52), athletic treadmill testing located my lactate
threshold (4.3 mmol) in running at about 174 bpm (max of 184, VO2max
58).  In 2002, my x-c ski race average HRs in classical technique
on low altitude 15-30K courses ranged from 164-169 bpm (1-2:15 hrs).
The following year, 2003, on the same courses, same skiing style, my
average race HR dropped to around 155 and has stayed within a beat or
two lower since (per Polar Accurex Plus HR monitor). Lactate tests done
while classical rollerskiing the past two years have found a similar ~4
mmol HR point. While I haven't done a max HR test since 1999, I have no
reason from my training to believe it's come down appreciably, and that
Bruce test in June would seem to support that (I was at 162 bpm, mid
level 4 in my training, at 16 mins).  Overtraining is also not an issue.
I know that with age these capacities gradually decrease, but I've
always heard the drop (in HR) is gradual and slowed or even stabilized
with training. Is the kind of decrease year to year - probably within a
few months - I experienced normal or common, or is there something I
should investigate further?  Thanks.

Roger