Heart Signs

I believe I detect differences in my training heart rate trends now compared to a few months ago.

For almost a year now, I've been learning about and getting a bead on my heart rate signature, establishing my benchmarks for training purposes and health assessment.  At 49 years old, the standard rule-of-thumb guide is that my maximum heart rate would be around 220-49, or 71 beats per minute.  The caution about that is that it's just a guide and not a given.  Based on my experience, I believe my maximum heart rate is somewhere in the neighborhood of 175.  I also understand that whatever the number is, it's not something that I can change through physical conditioning.  If it's going to change at all, it'll come down as I age. 

But it's from that number that other training zones are calculated, factored as a percentage of that maximum.  I had concluded that the threshold (when running) between aerobic and anaerobic exercise occurred around the 90% mark, or around 158.  That seemed to be where my heart rate would stabilize on race pace 5K or 10K runs, and that'd be the point around which I'd go from maybe slightly uncomfortable to pretty vigorous and exhaustive breathing.  For shorter periods, I could get my heart rate up into the mid-160s, and at times even see 170 or a little more.

My concept of all this had been that with improved conditioning, I would see my lactate/anaerobic threshold increase.  Whereas maybe before, the threshold was at 85-90%, maybe now it would be 90-95%.

One thing I didn't expect was that I find it much more difficult to get my heart rate up that high.  It's true that my perceived level of exertion when around 158 is less than it used to be, but now I really have to push myself and get more uncomfortable to see my heart rate elevate into that 163-165 range.  I can't remember the last time I've seen it rise about 165, even though my level of exertion has increased and my speed and endurance marks have improved.

I wasn't sure what what going on.  Was my maximum heart rate dropping?  I don't think so.  I think that improved conditioning has resulted in a more efficient heart pump such that when working harder it doesn't have to pump as vigorously as it used to to circulate the oxygen my body needed.  At least that's what I think is happening.

It correlates to a reduction in my heart rate at lighter loads too.  A light or easy run used to mean a heart rate of around 145-148 bpm.  Now, I find that the same level of exertion results in a steady rate of 138-143 bpm.  I believe that's a direct indication of improved efficiencies in my heart, which is kind of exciting. 

I haven't noticed any differences in my resting heart rate.  I've always had a bit of sinus bradycardia and my resting heart rate ranges anywhere from 48 to 55; but that was true even when I wasn't fit.  I have noticed that my resting heart rate will be elevated for a day or two after some particularly strenuous workout days, but it eventually settles back down to normal.

I like metrics and bio-feedback, so it's typical for me to get fixated on things like heart rate measurements. I've tried to ween myself off of the heart rate monitor and rely more on my perception of exertion and ventilation indicators to assess how my body is doing at various levels of stress.  It takes time though and isn't as fun or objective.  I'd probably need the battery in my monitor to die before I could truly go cold turkey.

One thing that I'm keeping an eye on is my systolic blood pressure.  I've noticed a trending rise in that lately.  It's not always elevated, but it has been measuring 125-130 at times, which is strange since it's normally been well under 120.  I don't know what, if anything, is going on there.