Board Thread:Site Discussion/@comment-30940727-20170806154038/@comment-32566907-20180202173256

I think it's just some sort of thing where they absorb energy from other sources and their own adrenaline and sheer mental strength, which is why Izuku's that much stronger when fighting Chisaki to save eri (not mentioning 100%). I think that's why his veins get literally filled with energy when he uses full cowl. I also think that in the anime Izuku vs All might fight, that's why the lightning goes into him as he activates one for all. I also think that without realizing, his sheer haste to run away had boosted him past 5%, but that's speculation.

The closest way to this working i can think of is that during the early stages of having OFA, you rapidly increase in terms of strength, absorbing a stupid amount and then gradually slowing down until you started losing that energy and give away OFA.