Hanging from a bar (or rings) engage shoulders, and lift legs to at least 90 degrees. Squeezing the ankles together and keeping the legs straight, tighten your core, tuck tailbone under slightly and hold the position. When first working this position try to hold for 15 seconds. Once strength develops lengthen the amount of time.
Hanging in either a pullup grip (pronated) or chinup grip (supinated), pull until your arms are bent at less than 90 degrees. This movement is isometric, so we will be holding the static position for a length of time. It is important the elbows stay close to the body and not flared out to the sides.
Variations: Pulling until your chin is over the bar, and your elbow angle is compeletely closed, and hold. Or pulling until your elbow angle is 90 degrees and holding in this position.