Frankly, I'm not a big fan of 'pacing'. Go all out, run yourself dry, then take an extra break if you need it. Running the tank dry is, I think, a great way to make it 'bigger'.

That said, one possibility is phase I eating. For some people, this just isn't enough carbs. You crash and run out of energy. Phase II eating should fix this. This 'crash' is fully expected (see Steve's explanation of Phase I eating in the FAQ section).

Good Luck!

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