And there you have it folks, Luffy is literally killing himself to maintain this form:
"When Luffy loses all his energy, he remember before that he was about to die and realizes that this form consumes a lot. Kaidou tells him to rest in peace, someone will talk about this fight in the future(like what he said to Oden when he was about to die) but Luffy says if he dies here everyone else will become bones.
Momo says that Luffy's "voice" is about to disappear, Luffy says that he can't lose here and repeats 4 names, "Momo, Tama, Kin'emon, Pedro" while he does something, Kaidou realizes what that something is and tells him that he will die but Luffy keeps doing it saying "Get loud, heartbeat sound!" and recovers his form."