Thread:Desboy96/@comment-39268687-20190426152314/@comment-1706203-20190426165202

Are you caught up in the Manga? There's a panel in Chapter 172 page 15 that explains perfectly how Izuku uses Full Cowl. Before Full Cowl, Izuku would access 100% of One For All's power in a single body part. Then he learned how to channel a lower output in that single bodypart like 5%.

Thanks to Gran Torino, Izuku learned to channel 5% throughout his entire body, inventing Full Cowl. Full Cowl allows him to control One For All's output while its power is flowing continously through his entire body. After switching over to Shoot Style, he raised his upper limit to 8%.

Izuku can still access any percentage at any time, but going over his limit with injure his body. Currently, Izuku can push his limits and use 20% of One For All for a short period of time, but even this hurts his body and is difficult to maintain.

I hope this helps.