We are a commune of inquiring, skeptical, politically centrist, capitalist, anglophile, traditionalist New England Yankee humans, humanoids, and animals with many interests beyond and above politics. Each of us has had a high-school education (or GED), but all had ADD so didn't pay attention very well, especially the dogs. Each one of us does "try my best to be just like I am," and none of us enjoys working for others, including for Maggie, from whom we receive neither a nickel nor a dime. Freedom from nags, cranks, government, do-gooders, control-freaks and idiots is all that we ask for.
How often do you feel "bursting with physical energy"? It's a wonderful feeling. We see it in kids all the time. They have to run, have to move, have to dance, have to climb, can't sit still. It's hard to know what it's about, though.
Feeling as energetic as a 7 year-old, with that need for physical activity, is rare in those over 30. A sedentary lifestyle (roughly defined as less than 6-8 hours of exertion/week - not including walking unless elderly) is a mental habit rather than a measure of any sort of true physical "energy." Energy, however, accrues to the energetic even though we will never be 7 again.
I make distinctions between these biological and psychological things:
1. The drive, need, and desire for challenging physical activity that derives from high fitness (Get Up and Go is a result of fitness + attitude), 2. The ability to recruit the mental energy to complete hard things in a dutiful way or with external demand, but without the need or drive to do them (70/30% mental/physiological), 3. The state of one's capacity for muscular and cardiac function (100% physiological) 4. "Low energy," aka "laziness", ie lethargic life habits (90% mental, but the physiological obviously deteriorates rapidly with disuse).
OK, so subjective "energy" is not mainly related to actual physical "energy". Same word, different things. #3 is of most interest to me even though it has nothing to do with how much Get Up and Go you feel when you wake up in the morning. I have a strong bias in favor of those with that Go Go attitude regardless of age or physical conditioning.
Energy details below the fold -
So let's put the subjective experience of energy aside and just consider the physiology of cardiac and muscular energy. These are kinds of energywhich are not usually "felt" except in their absence, but are just there as resources.
At the macro level, the ability to do physical work relies on neuro-muscular connections, the number and size of contracting fibers inside your muscle cells, and blood supply to muscle. All of those are improved with strenuous exercise - including cardiac muscle.
On the more interesting micro level, the energy that keeps us alive is generated inside our mitochondria. (Yes, plants have mitochondria too.) Interestingly, the number and size of cellular mitochondria is increased by exercise (mitochondrial biogenesis).
All three energy systems can be trained for efficiency, to varying degrees. Phosphagen is the least-trainable.
The causes for short-term muscle fatigue are clear: phosphagen and glycolysis are exhausted quickly unless given a few minutes to replenish. That is why you can't do one more bench press, but the causes of longer-term muscle fatigue remain somewhat mysterious under normal conditions.
Why are your legs tired after a 6-hour mountain hike? It's not entirely understood, but the best guess is that it has something to do with glycogen depletion. It's a bit confusing, because gycolysis is a short-term energy source yet it is constantly trying to replenish. Regardless, trained athletes can have double the muscle glycogen stores compared to ordinary people. Studies seem to indicate that HIIT training is the best way to increase one's glycogen capacity and to extend the time at which fatigue occurs.
Despite these confusing aspects, it is never a bad idea to take in some sugary drinks during an extended exercise session or extended physical effort. Assuming that you are not fat, not doing that can be one cause of "overtraining" in which your body is forced to break down muscle protein for fuel. That is not much of a danger if you have some pudge on board, because fat is an excellent, if slow, fuel source.
Old age and major surgeries have sapped my energy. I may feel good but doing anything physical quickly becomes unsustainable. Two lung operations to remove two lobes. I joke with my oncologist that we can't keep doing this. I miss the old me, the energy and exercise. I still hang in their, hike, walk, work around the house, but I must pace myself.
Funny true story; Two years ago I was hiking up Bright Angel Trail. I didn't hike down that far but any hike uphill is a struggle for me. So I was struggling and it was close to noon so it was warm. Most people who pass you on the trail say hi and keep moving. This nice lady passed and turned to me touching my shoulder and looking right at me asked "are you all right". I bet she was a nurse or doctor and was quite concerned about how bad I looked. I answered that I was fine and she went on up the trail. Once I got to the top I was fine, tired and a little dehydrated but fine considering I had hiked up 3 miles.
So enjoy the energy while you are young(er) and exercise to stay young for awhile longer. Soon enough you will miss the old you.