Even though the sai are sometimes called "short swords," they were not used as a sword would be used. Sai were primarily a defensive weapon, much as the way a club would be used. Some of the major techniques with the sai are:
- With the blade retracted, the sai covers the forearm to augment blocking techniques. Also, the butt end may be used as an effective punching implement. When held in this position, since the kimono had very long and baggy sleeves, the opponent cannot tell exactly what you are holding or the length of the weapon.
- After flipping the long end outward, it may be used as a whipping or striking tool or for poking and blocking techniques.
- The butt knob may be used for punching techniques or for pressing on nerve centers and pressure points.
- Many believe the prongs were used to catch and trap a strike from a weapon, such as sword or a bo. Once the prongs complete the trap, the defender may use the sai to twist the attacker's weapon from his grasp or even break the weapon. However, the range and momentum generated by a longer weapon, such as the bo, would make this a risky defense. Although this type of defense may be effective against a short weapon, such as a knife. Prongs are used to protect the hand from injury.
There is evidence that the sai was used for "hojo undo" or endurance training. While it is possible that the native martial artists used these heavy sai for fighting, it is more probable that they were training tools used for developing arm and wrist strength. Because of the flipping techniques employed in use of the sai, strong and limber wrists need to be developed if one is going to master their use. For this reason, modern martial artists use the sai to supplement their training.