Well, to add to the discussion.... you need to have good nutrition to take you to the next level. You need to eat enough, eat the right stuff and at the right times to get a good training session in.
I know if I don't eat enough during the day, my training session at night suffers.
As far as taking it to the next level... you have to come to understand that even if you are sore you can still pedal a bike. You can still run. So many people have sore muscles and think "I need to rest". Being a little bit sore, doesn't mean you get to rest. Especially if your training plan doesn't call for it.
We have become a society where pain is not embraced or seen as good or helpful. Now, there is a difference between pain and suffering. I guess what I'm talking about more is suffering. If you have accute pain, which will lead to injury then stop. But if you are simply suffering... keep moving forward.
With my IM training, I have 3 hard weeks of training and then I get a recovery week... that is what my coach has me doing. Those 3 weeks are hard. I'm sore. He doesn't care. I have to keep training. It's how it works.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"