If there's one thing a person should respect about Sumo, it's their ability to maintain balance. They have to deal with 300+ pound monsters charging at them at full tilt and with that weight, be hit so hard they're thrown away from the force. The reason they practice the leg lifts is to grow stronger trunks (hips and leg muscles) = stronger balance and resolve. In martial arts, eastern and western, you need strong legs to take hits, as your legs are taking the brunt of the force of impacts. So it makes sense that a Sumo wrestler could get up after taking those hits, then again, he's also taking the supposed Supersonic strikes from Katsumi too, which borders on suspension of disbelief.