[Uppndownn]

Assuming you are playing right handed, the left arm should be extended (or near straight) pretty much from address through impact, and then fold. The right arm extends through and after impact. As the left arm rotates, it facilitates the full extension of the right arm to the both arms straight postion, a little after impact. That is my view, but wiser posters will clarify it on this site.

UPP in snow covered Ohio