Now, if one thinks about survival when there are big, hungry carnivores around, one would recognize that, the Maslow scale is correct: if physical safety is at risk, everything else can go hang.
The American Heart Association captures this in their "exercise" table:
Ideal For |
Benefit Desired |
Intensity Level (% Maximum heart rate) |
Light Exercise |
Maintain Healthy Heart/Get Fit |
50% - 60% |
Weight Management |
Lose Weight/ Burn Fat |
60% - 70% |
Aerobic Base Building |
Increase Stamina Aerobic Endurance |
70% - 80% |
Optimal Conditioning |
Maintain Excellent Fitness Condition |
80% - 90% |
Elite Athlete |
Maintain Superb Athletic Condition |
90% - 100% |
So, why stop at 70% if you want to "lose weight"?
The "secret" is that "burn fat" stops at about 70%: if a person's MHR is greater than 70%, the body doesn't waste the O2 to convert fat to glucose. When I checked, that conversion was pretty expensive in terms of O2 need and, if you're trying to outrun a lion, it likely isn't too important.
So, why stop at 70% if you want to "lose weight"?
The "secret" is that "burn fat" slow/stops at about 70%: if a person's MHR is greater than 70%, the body doesn't waste the O2 to convert fat to glucose. When I checked, that conversion was pretty expensive in terms of O2 need and, if you're trying to outrun a lion, it likely isn't too important.
The best way I have heard of is to have a formal "treadmill test". I had one when I was 39 (long ago). The cardiologist (yes, a real, live one) hooked me up with a lot of wires to watch my heart rate, etc, and took my blood pressure every couple of minutes. He put me on a treadmill and told me "hit the stop bottom when you feel you need to" (??? what a thing to say).
Well, I'm an over achiever. I just kept going and going as the incline got steeper and steeper. I finally said "enough" and hit the button. The Doctors commented "good, I was just about to stop it. See these little 'glitches; on the heart graph? Your heart is starting to miss beats which means you needed to stop...".
=> turns out the max was 196, gee, I must be 24 (again :-)
Back to that Century Ride: it seems I had determined my current maximum heart rate on my own, and probably with a chance I could have done myself in.
I had valiantly stayed up with them.
The flats were fine (but hard) and then we came to Clapshaw Hill: while keeping up, my heart rate when up to 183 bps! Wow! I'd never see it that high, so I slowed a bit more as I went up the hill. (and worried a tiny bit about whether I would keel over...).
But then I noted that my heart rate when up to 188bps!! All this is recorded in my Garmin Edge 305 so I have it in "electrons". I note that 4 hours later, on the steepest part of the ride, my legs "gave up" and started cramping, but that is a different story and likely not related to MHR.
At my age, it is amazing that I simply didn't keel over; a definite possibility (note to self: don't do that again without a doctor present!).