In fact, it involves strenuous breath control and of all techniques, it's the most difficult.
7 seconds sound clip from the The Invincible Armour movie soundboard.
You can hear this line at 00:00:32 in the DVD version of the movie.
Quote context
[...]
- Iron armor, of all the Kung Fu techniques, is the most mysterious.
- With it, one can stand blows from swords and stabbings from spears. One is invulnerable.
- In fact, it involves strenuous breath control and of all techniques, it's the most difficult.
- The human body has 108 pressure points.
- Thirty-six of these can be fatal... to the remainder, paralyzing.
- To learn iron armor, one starts with the breathing.
- Then the body's completely protected and thus invulnerable.
[...]