These names are according to the classic 24 styles (as per text by Wang Dixian). Mantak Chia combined the two into one name "Holding the Golden Urn". Chia probably learned it through the Cheng-Wu tai-chi lineage in Hong Kong.
Anyway both styles make use of the palms to hold an imaginary Golden Urn (or "One", signified that GU is only an imagery without any metaphysical content!). With an imaginary something being held up (and balancing it on one's palms at the same time), a practitioner's extension muscles will be activated and exercised accordingly.
In more recent literature, I read about a tai-chi master, who is famous for training his students to take part in MMA fights, made use of spherical balls of some weight hanging down (by a string) to replace the imaginary golden urns. For general workout purpose, something imaginary will probably be sufficient for most practitioners.
|Mantak Chia doing Holding the Golden Urn|