Between a hectic day when I have to be on my feet all day and a day spent just sitting in the car or on the train and looking out the window, the latter feels 10x more exhausting.
Why is this? If you’re not the driver, you barely have to do anything on those long trips, and yet they’re still so tiring for no reason.
Road trips are tiring even as a passenger because I’m still “alert” as if I were driving, assessing hazards etc.
I find train trips are more relaxing, although there is stress/anxiety if you have to change trains and connections are tight etc. Also if it’s a stopping-train in an unfamiliar area, then I’m alert to other people, and whether they’re going to be unruly or any kind of threat.
Another reason is that sitting requires some muscles to permanently be clenched or partially clenched, without rest. Clenched muscles require a steady supply of nutriments to stay clenched, even if the load isn’t so heavy, and over hours that accumulates. That is also why, for example, it feels so good to stretch your legs every so often. Better ergonomic in designing car seats combat some of that, so does the ability to lower your seat, but that won’t help on a cramped train or plane ride.
The brain thing mentioned earlier is also another reason.
The brain is a predictive machine with the theory that consciousness is only a product of “incorrect predictions.” This is why if you move to a new city and walk to work, on your first day you will be much more conscious of all the new sights and sounds. After walking that route every day for a year, at the end you may walk the entire way and it felt like it happened in the blink of an eye or you were in your head more and didn’t “notice” as much stuff.
It could be that when you’re in a car or a train there is so much “new” stimulating signals that your brain is much more alert and processing so much more than if you were sitting for an equal amount of time on your couch at home.
Your body adjusts and compensates against every shift of the car/carriage, like you’re constantly bracing yourself. That’s a lot of work, and tiring.