Overstand is totally right!
I've been training at 6am in the last year and a half... I'm off to bed at 9pm, get up at 4.45, drink a protein shake with rice cakes at 5-5.10, start loosen up my hips-shoulders 20 min before training, start training at 6am.
My CNS "doesnt require xy amount of hours to function properly"... don't forget, symphathetic stimulus activates fast and has a long-lasting effect. It takes more time to "cool down", or to turn off yourself.
And you know what? At this gym, there are always 10-15 people at early morning.. They apparently have problem with CNS activation.
Otherwise, the best is to start the workout with some compound movement, ramp up. Everything will feel like child's play after that..
Heck, this morning my hip-knee-ankle joints were so good that I squatted with 300 pounds at 6.10am without any difficulty. The body will adapt.
And after long months of training early, I've learnt how to "turn on" myself after just a few minutes. It usually takes only a few minor sets of some compound to start the blood running, then I'M good for everything.
Oh, I'm only 20yers old, so I don't have problem with joints-tendons-ligaments.. But I've attempted to train at 8am when I was 17 and it was hell, literally. But the human body has incredible ability to adapt.