C975 Power of Thunder and Fire
In battle, both sides would often have the ability to draw on each other's Qi. Normally, when a martial artist reached the Tempered Body Refinement realm, they would have this ability.
However, this wasn't absolute. It depended on a martial artist's combat talent, as well as their combat experience.
Zuo Feng was one of the best in this area. When he was at the Bone Refining stage