Nerves to muscles die. Mitochondria become less efficient. Tendons and ligaments grow less flexible as they crosslink through the Maillard reaction.
All are irreversible processes. Well, some reenervation is possible.
If you don’t exercise regularly after 50 or 60, you go downhill faster than when you were 25.
Less testosterone for the men too. That makes getting back in shape harder
“Energy” is a pretty broad term, if one wants a serious answer. Power, endurance? Physical capacity or mental eagerness? Literal metabolic efficiency?
There are without question real physiologic impacts of aging on all of those. The open question is not whether those impacts exist but how big they are relative to the impacts of lifestyle choices, both when younger (how much is in the bank) and ongoing as we age (making more deposits even if small or making withdrawals, and then how fast).
Both play roles in loss of power, endurance, and even energy for novel cognitive work associated with aging. How much each? Unclear. The aging clock itself is slowed with regular exercise and healthy nutrition choices.
Can stop there.
But if one wants to use our Hunter Gatherer ancestors as the evolutionary archetype then those who survived young adulthood (not dying a violent death or in childbirth) often lived quite long and fairly well.
There are many physical effects of aging that cause low energy levels, including limited blood flow, slow metabolism, and interrupted sleep patterns.
Our bodies, all living things, are engineered to work for a finite period of time.
But the overwhelming majority of people fail to maximize their potential energy, which is why people notice a dramatic change in energy levels if they shake up their routine in mid-life.
As a result of modern living, a majority of people die slowly, with their bodies gradually - sometimes painfully - breaking down over a period of years or even decades. If we take care of ourselves and maximize use of our bodies, we are more likely to simply go out like a light bulb when we die. That’s the ideal way to die.
I went looking for evidence for my pet theory, but I couldn’t find any. On the other hand, I couldn’t find a clear rejection.
As we get older, our cardio-respiratory system becomes less effective. Blocked arteries and reduced lung function contribute. As a result, we have less ‘energy’. You can replicate this effect by going to altitude: you can reverse this effect by blood doping (as demonstrated on my mother). I experienced this effect by living at altitude and then coming down to sea level: my nephew experienced it by living at sea level then visiting Nepal (‘Slow down’ they told him. ‘One step at a time’.).
You’re welcome to my theory: remember, it’s not a medical theory, it’s just something you read on the internet.
I think your theory of reduced cardio-respiratory function is correct, but also: everything else
We’ve had this come up a few times before on the Dope. For example, I recall a thread where someone asked why old people don’t run up stairs (seriously). People were trying to think of the one thing that is responsible. One person would say it was joint mobility. Another would say muscle strength. And then, yes, cardio-respiratory function decline.
The answer is of course all of the above, and any other involved system we could care to name. It all ages.
Yeah. I recall a thread where I said old people look old on the outside; e.g. wrinkly, thin hair, blotchy skin. Then I asked: do their innards look aged too? To which the medics more or less said: “Yep”.
IOW: Like ugly, old goes clean to the bone.
Then again, the alternative would be worse in a way.
My very aged MIL is getting pretty raggedy but is still going. She finds the infirmity, and all her generally cranky creaky parts & pieces to be a PITA. I pointed out that that’s a good thing.
Me: You’re wearing out your whole body. If you died while any part of it still worked well, you’d be wasting it. You’re a Depression era woman; you know never to waste anything. What’s that motto you’re always quoting: “Use it up, wear it out, make it do, or do without”?
She laughed and said I had a point. “100 or bust” is her new motto. She shook off COVID like it was the sniffles. It’s plausible she’ll make it. Go Mom!
It’s all about getting older man. All of us getting older and it’s a normal thing. It’s possible to slow this process by eating right and doing sports.
Yes. There are multiple possible reasons.
As I understand it, there are three broad types of reasons why older people may lose the capacity to do what they did when they were younger:
(1) the natural effects of aging—the body just “wearing out”;
(2) the lingering effects of illness or injury, not directly related to age except that, the older we get, the more chance we’ve had to experience such illness or injury; and
(3) “use it or lose it”: when we stop doing something, our ability to do so atrophies.
That’s all true, however it’s also true that many of the effects are non-linear.
Or rather; we seem to age in a linear fashion between roughly, 20-40, then after that the decline steadily accelerates.
This is one reason to favor “programmed” theories of ageing, like telomeres, cellular senescence, mitochondrial dysfunction etc.