Type-2 diabetes is supposed to be caused by insulin resistance.
You can become resistant to your own proteins.
This would include proteins like adrenaline.
Peak human abilities - the zone, inspiration, and so on - are caused by the release of special-purpose proteins. For instance in most times your muscles will not work to full capacity. (Chimps have been measured at pulling 900 lbs with one arm. Humans average 180. I'm sure we could do better without structural damage.)
The reason that the times and days where one works best is limited is not because of structural limits, such as the rate at which we repair stress, but rather limited by the body's ability to adapt to chemicals, whether foreign drugs or internal proteins.
Even if you turned the inspiration molecule up to max, you would adapt to the new level and function as normal - but without the ability to become inspired.
And that's why the full human potential is so hard to actualize. This explains things such as the inconsistency of a single author's writing, for example.