are Oi Tsuki (lunge punch) and Gyaku Tsuki (reverse punch).
There are many other types of punch and variations on these two basics. The classic delivery stance is Zen Kutsu Dachi (forward leaning stance). However, Sanchin is also used extensively in Goju.
It is important to keep the shoulder down. This then allows the Pectoral and Latimus Dorsi muscles of the chest and shoulder to contract properly and give support to the shoulder. The hip position and back are also important for maximum power.
The back should be straight (not vertical) and have a slight lean forward with the hips tucked slightly up to engage the Psoas, Rectus abdominus and Spinus Erectus muscles of the mid section.
As in all Karate, proper use and training of the core strength muscles of the abdomen are vital for strength and power.