Originally Posted by MoAlpha

Great effort! The next one will be easier.

Lower back: As others have said, you need to get used to spending time in that position. However, I strongly believe that being comfortable on the bike, particularly low and comfortable, is largely a matter of strength in the posterior chain, centered around the glutes, which support the lower back and spare the paraspinal muscles, which are what hurts. This is why I love deadlifts, but there are lots of great exercises which will do the same thing.

Hunger: Your liver and muscle glycogen stores are gone by about 90 min. After that, you need to live on ketone bodies from fat and make glucose out of other molecules. Those processes involve enzyme systems the genes for which aren't transcribed into proteins (enzymes) at high rates unless we need them. If you go out in an untrained state and burn up your carb stores, you can go right into a state of energy collapse with lots of attendant hunger and stress. Long rides turn up the rate of gene transcription for those systems which mitigate starvation and soon you'll be able to go for hours without eating or getting hungry unless you're like WhyFi , in which case you will have to stop for donuts. : Þ

Leg pain: Probably related to metabolic stress. Again, training.