The Siu Nim Tau introduces the single punch (straight-line thrusting punch) as a prerequisite to the chain punch. The motion of the single punch, along with the circling hand, develops the path and structure necessary for a safe and powerful chain punch.
When extending the punch in the air, be sure that the fist starts at the center-point and extends up to throat level when thrust forward. The air punch should be fully extended or locked out in order to call upon the correct muscle groups. If done properly, the triceps and the lateral muscles are the primary muscles engaged. Refrain from tensing or extending the shoulders. If done properly, the triceps and the lateral muscles of the back are the primary muscles engaged. Keep in mind that locking the arm out should only be done when practicing in the air, and not on a wall bag or target. The arm is locked out in order to allow the full power to be utilized.
After the punch is extended the huen-sau, or circling-hand, is employed in order to develop strength and flexibility in the forearm. To perform this open the hand palm up while keeping the elbow fully extended. Bend the hand back at the wrist, refrain from curling the fingers. Twist the hand down 180 degrees, with the fingers still extended straight. Roll the fingers into your hand and end with a horizontal fist. Then chamber the arm. If this is done properly, the forearm muscles should be flexing just before snapping into the fist position (as seen in the image below).
The single punch exercise with the huen-sau needs to be given special attention in order to reap the benefits of this often glossed-over portion of the Siu Nim Tau. I encourage students to practice sets of the single punch with huen sau while holding the character two stance. These simple movements, with effort, will develop power in the punch and hands of the contentious student.