Isshin-Ryu Karate is a style karate founded largely a synthesis of Shorin-Ryu and Goju-Ryu karate. The name means, literally, "one heart way" (as in "wholehearted" or "complete").
Isshin-Ryu employs a vertical punch with the fingers tucked in and the thumb on top of the fist. Advantages vary with opinion, but it is usually taught that the thumb placement increases the stability of the wrist when punching, and that a vertical punch strikes with the same force at any range instead of at maximum extension as with a corkscrew style punch. Another advantage is that when punching, the thumb will not get caught on an object as opposed to having the thumb sticking up or out.
In Isshin-Ryu it is believed that the vertical punch is faster than the cork-screw punch: three vertical hand punches can be generated in the time of two cork-screw punches.
Isshin-Ryu arm blocks are performed today with the muscle at the intended contact point as opposed to other styles that block with the bone. By using the two bones and the muscle to form a block, less stress is created against the defender's arm, increasing the ability to absorb a strike.
The original arm blocks were taught with palm up, wrist bent, to form a trapping motion as well as to block and/or strike with the radius bone.
Isshin-Ryu kicks are primarily a "snapping" motion, as opposed to placing primary emphasis on thrusting and follow-through. Furthermore, Traditional Isshin-Ryu kicks are aimed almost entirely to the legs or groin. Nothing above the belt.