Sanchin has no prescribed bunkai, it is a training kata. It is considered a “Closed Hand” kata, or Heishugata. This doesn’t mean that your fist is physically closed, it means that your body remains tight and firm under dynamic tension throughout the entire kata. This helps build endurance and strength. The kata was inspired by an ancient White Crane form called San Zhan that aims to train the same things.
Sanchin improves your physical strength, your general health, blood circulation, lung capacity, and perhaps most importantly, your mind. The name translates to “3 Battles,” and many interpretations of equal validity can be used to improve your understanding of the kata.
As you further your comprehension of the kata, you should think about how motions or principles within it can relate to all of your other kata, kihon, or kumite.