The Effect of Exercise on the Brain

Do we know what percentage the brain controls that process versus the muscle? And if we don't, is it, are we all on different sliding scales? In other words, does an elite athlete have the ability to push further into that zone where the brain is almost switched off to the muscles? Or does something like me, who can only feel tired when my temperature gets to 39 or my metabolites or a certain even in other said, can you shift that? Is there a difference between what elites can shift versus normal people? Almost certainly yes, but I would be cautious to reduce it to just the fact that elites can tolerate homeostatic discomfort for longer.