Vaisampayana said, “Then contracting that huge body of his, which he had assumed at will, the monkey with his arms again embraced Bhimasena. And O Bharata, on Bhima being embraced by his brother, his fatigue went off, and all (the powers of body) as also his strength were restored. And having gained great accession of strength, he thought that there was none equal to him in physical power.

In plain words: Hanuman shrinks back to normal size and hugs Bhima. The hug takes away Bhima's tiredness and gives him so much new strength that he feels no one is as strong as he is.