Final answer:
The question seems to refer to body movement involving arm extension, likely related to supination and pronation of the forearm. Elbows can be slightly bent, and palms positioned forward in supination or backwards in pronation.
Step-by-step explanation:
The instruction seems to describe a variation of a position requiring arm extension. While the specific pose "JACKKNIFE" is not a standard anatomical or exercise term, it could be related to body movements such as supination and pronation, which are movements of the forearm.
In supination, the forearm is rotated so that the palm faces up or forward, while in pronation, the palm faces down or backward. In terms of elbow positioning, a common instruction might be to keep the elbows slightly bent or soft to avoid hyperextension. Regarding the palms, they could be facing in various positions depending on the specific exercise or motion, such as forward in supination or backward in pronation.