Not talking about the low resting HR improving by exercise.

I was under the impression that the max HR is generally very rigid with slight decreases occurring as age takes its toll. A few weeks back, my max HR did a step-function like change, and has been stable at the new point since then, it was large enough to shift the numbers that I use to limit how much high intensity sprinting I do.. It was about 175, and now its a good 183-185. Resting has remained at 55 or a bit lower. I don't really mind, as maybe I can pretend to be about 5 years younger??? (i'll be 48 soon)... 1 min recovery remains a respectable 35-40bpm.

Power and endurance didn't seem to change noticeably, just the numbers that I see on the HR monitor's output at different exertion levels. (and no, monitor didn't go nuts, compared it with other monitors, and its fine).

Is this odd, or am I mistaken about maxHR in the general population? I was just really caught by surprise by the change.

I would say that the only thing we know about Max Heart Rate is what we have sampled. We know that it tends to decline with age but we don't know what limits it or why? Are the limits electro-chemical? Or are they mechanical limits? Nobody knows. And equally, we don't know why max heart rate is different in different people of the same age. All we know is: "If you are this old, it tends to be 'this', and it tends to not change (at least it doesn't tend to increase).

Sort of like a weather forecast based on: "It has rained 7 out the past 10 years on this day".

For myself, my speed and and heart rate increased by 10% after I started taking Q10 to offset the effects of aging and the statin I have have taking...

Does that contradict the conventional wisdom that max heart rate can't change? Not really, I changed the chemical equation -- so the result of that equation (my heart rate stats) changed too...

The heartrates I achieve in the summer are higher than I see in the winter. Heat and dehydration are factoring in.

I also get a higher heartrate while cycling than I have when swimming. The cool water and horizontal position make it easier on the heart.
Swimming butterfly I still don't get the same heartrate as cycling uphill. (I have a competitive swimming background)

I will hit higher heartrates on a ride if I have had a fear episode earlier that day - driving/riding in scary traffic or being chased by a dog.
A hard hill that I struggle on also makes me more aggressive and I cannot ride socially afterwards, I just want to hammer not yammer.

I took a maximal stress test age 37 and have hit the same heartrates on some steep hills this summer age 57.
When I was a teenager I would hit much higher heartrates so there has been some decline over the years.

There is no reason our hearts can't do 250 or 300 bpm if our brain told it to. As it happens it only beats fast enough to provide oxygen and cooling as needed. As you become fitter it is not unthinkable that your muscles are working harder and require more oxygen and cooling.
I have noticed that when I started cycling seriously at 35yr, 170 bpm felt like I was going to collapse, while now 175 feels intense but doable and I max out at 182.

Also it is not adviced to base HR zones on Max HR, better to use LTHR.

This is a technical point, but: Our brains do not control our heart rate (except indirectly via such things as adrenaline or the vagal response). The heart has its own baroreceptors and its own electrical system that control how hard and how fast it beats. And, for some reason not completely understood it does tend to beat slower and slower as we get older and older. For instance, the resting heart rate for an infant of up to 160bpm (with the average being 120-145) can be as high as the maximum heart for an older person.

But that doesn't change your basic point: The heart can beat as fast as it wants...

My (rhetorical) question is: why does it slow down with age? What changes to make it slow down and the max decrease?

Medical science seems to just shrug and say: "It slows down because you are older"... But that avoids the question rather than answers it -- and neither does it answer why some people (like you) are able to maintain their max heart rates as they age.
.... BTW: Good Job!

It is odd, I've reduced my HR numbers overall after 7 months of a dramatic diet change and adding more running to my work-out week. My peak and zones seem to have dropped about 20 points across the board, resting HR dropped about 4 points. I'm not complaining, but the why is a mystery. There are so many variables; even breathing through your mouth vs. nose is argued to increase your HR by as much as 10 bpm.

Am reading about the Tarahumara, .. a marathon a day on little more than corn beer...and no power bars.

Well, now is only 1 year later since I started cycling so I am still only 36yr old and max of 182 I have seen during short hard efforts is close to 220-age. I have never tried a max heart rate test as I understand that requires somebody with a gun behind you.

So I assume that when people talk about the heart slowing down with age it is for comparable efforts? So is the oxygen consumption then still the same and can older people somehow bring more oxygen to the muscles with less blood?

I don't know. I don't think anybody does...

But I do think that for many, many years medical science has simply assumed that things like fraility, dementia, heart disease and the like are simply ramifications of aging rather then preventable illnesses -- so they have never really investigated things like why our hearts slow down as we age. Simply put, that goes against the norm and there's no money in it for them.

Thanks for all the replies, I'm going to bet its "summer heat/dehydration" for now. Be interesting to test it in winter, indoors on the stationary to see what happens.

It's just as likely that your previous estimate of your max HR was not correct.

I had a little over 12 months of interval testing to back up the previous estimate, and then *poof* it step-function changed on me. It was almost as abrupt as the time I changed meds a long while back. Still not out of the question though. Maybe if it doesn't drop back down when I go indoors, I'll just consider the old estimate erroneous. Whatever it is, the old number is clearly wrong now, last long ride I had gave me nearly 2hrs in zone 5/redline which just can not be right. lol.
https://www.sportstracklive.com/track...ycling/1182636
nb.. before anyone heckles my speeds, its a hybrid with a touring load, full paniers, about 100lbs...

Watts at LT goes down with age. That's why we have age classes for sports. MHR goes down even if one continues to exercise strenuously. At 55, I could hit 184 during an attack. At 68, I attack at ~160. LT at 55 was ~162, now ~149. Nothing to do with mentality. It just goes down as we age. However, a lifetime commitment to training will slow the drop-off, possibly to about 1 beat/year.

MHR and LTHR also vary with training state. Once one is highly trained, training stress will reduce both numbers. Laying off for a few days will increase both. Watts won't vary as much as HR with training stress.

Effort is not the same as result.