GURPS Powers: Enhanced Senses

[Bruno]

Originally Posted by Irioth

A few primates (e.g. gibbons) use bipedal walking as a secondary locomotion mode, yet their excellent brachiation suggests they have a better sense of balance than humans.

Their excellent shoulder flexibility, long arms in proportion to low body weight, and hook-like hands that are poor at object manipulation or throwing are major contributors to gibbon, siamang, and etc spectacular brachiation skills.
I don't see how balance is a big factor - with brachiation you don't fall off of a branch because you wobbled and dumped yourself, like a scansorial climber such as a squirrel risks.

Hanging is wonderfully self-stabilizing - there's some great science class demonstrations involving hanging various funny-looking weights off a table to demonstrate how this does great things for your centre of gravity. As long as your hook (hand, sloth-claws, whatever) is large enough to wrap around the tree limb and strong enough to keep the hook shape while bearing your weight (quite easy for the little brachiating apes, like gibbons) you're not going anywhere unless interfered with or your hand gets tired.