Are you setting up and adjusting the bike to fit you? As someone who has to adjust everything to fit myself it seems odd how common it is for riders to not even do basic adjustments on their bikes to work better for them, Dave Moss has a lot of fantastic stuff on this.
As someone who grew up doing upholstery I would say this definitely includes the seat and making sure it is raised/lowered to the right height for you and that the padding is sufficiently firm enough that you don't end up bottoming out on long rides. In my experience people most often think they need softer padding because of soreness issues, when in reality it is MUCH more common that their padding was already far to soft and they were bottoming out. I liken this to suspension: the harshest ride is when your suspension is so soft that you are constantly bottoming out and getting hard locked, stiffen up the suspension to where it should be and suddenly the ride is much less harsh and far more forgiving.
Honestly as long as my bike is well setup to me and I have reasonable wind protection longer rides are one of the least exhausting parts of riding, but obviously there are a lot of variables there so YMMV.
You dont have to answer here, but have you had your hormone levels checked? Seems most normal doctors have to be practically threatened with violence before they will check basic hormone levels, but that is a huge part of what makes us who we are. I know age is a big component here as well, since I am just over half your age, but a few years back I found out my testosterone was tanked to a level of around 200ng/dl total testosterone and pretty much 0 free, which isnt terribly abnormal for an 80-90 year old man. After starting on HRT mine is now more like 800-1,200ng/dl total with about 50ng/dl free and my endurance is TREMENDOUSLY better. I also just stacked on a fair amount of muscle passively in about the first 6 months on HRT and feel WAY better.
As a bonus tip for those of you that are either with or are women around middle age or later: while it is even harder to get doctors to admit women need testosterone, let alone check it and adjust it, it is very VERY much worth it to get it checked and adjusted to the higher side of normal feminine levels. As much as adjusting my testosterone made a difference, if my wife and I could only afford to keep on of us on HRT it would DEFINTELY be her. I am not going to go into specifics, but trust me on this, it is 100% worth it!


