I’m interesting about the physiology of energy, in a few word.

1/ you need to have sufficient production of ATP for mitochondria. If you have a problem of the production of oxidative stress (pollution, heavy metal, HCSF…) your cell produce peroxinitric from NO that down regulate the krebs cycle (aconidase) or OXPHOS (down regulation of complex 1 to 4)… Result is low energy

2/ You need the bosster of T3 and DA for energy

3/ energy loss from infection and inflammation