We use the slapping bag to train our Iron-Palm or Iron-Fist. Martial arts trains us to fight against humans, and man is not made of wood nor stone, therefore there is no reason to hit anything harder than cotton inside leather.
We are not liable for any injuries you incur by copying the exercises in this video! As with anything martial, be careful when trying the lessons here without some formal training. It is very important to make sure you use only up to 30% of your maximum total capacity. 😎