Most insidious of all was the complaint of the body. His body didn't like the pressure and wanted it to stop, so his body kept urging him to surrender.
His body was like a traitor for the enemy. It was demoralizing him.
Even if his body could continue to endure the physical pressure, he still had to contend with the internal pressure from his body urging him to quit so that the pain would be over.
Fortunately, he had the dominating fire intent flowing through his blood. He had already made up his mind not to quit. No matter what his body says, he won't quit.
It is just like Augustus telling him to let go of those snarky youths who made fun of him. He didn't listen to Augustus back then, and he won't listen to his cowardly body right now either.
Be that as it may, sometimes the situation is bigger than one's capabilities. As they say, the mind is willing, but the body is weak.