CoQ10, or better yet, ubiquinol.
I am horribly out of shape, but even in my better years, the trip to mammoth from SoCal absolutely killed me the first couple nights. SO...one year I started a CoQ10 regimen a week before, and every day during, in addition to ginger capsules for stomach upset, and valerian to help with sleep at night and I felt and rode much better. Actually slept the whole night through even the first night.
Ubiquinol, if I understand correctly, is CoQ10 for older bodies.