The description in the Daizenshuu is vague, but it makes it sound as though it works similarly to Grade 3.
I don't think there's anything special about it aside from the fact that he is using his ki to pump up his muscles. As for Piccolo Daimao, I'd highly doubt it even when Roshi was in his prime.
Chapter: 135, P6.1
Kame-sennin: “Despite the cute name, he was an outrageously fearsome person…His strength was extremely overwhelming…[ ]
He was an opponent we were utterly unable to oppose; not only my younger self or Tsuru-sennin, but even our master, Mutaito. ”
Chapter: 142, P3.6
Context: Kame-sennin, Tenshinhan, and co. search for the dragonballs
Kame-sennin: “
But we have no chance of winning if we run into them directly! Our only chance is to take advantage of an opening, steal the dragonballs, and leave it to Shenlong…ask him to destroy Daimao.”
Roshi makes it pretty clear that they can't beat him without stealing the Dragon Balls. A Taiyoken + Roshi Kamehameha wasn't even considered an option.