Definition #1:
To move around with arms held above the head in the manner of an upright crab.

Usage: Crab's evolution is such that by 2050 they will all thrutch upright

Definition #2:
The action of hip movement with or without a sexual partner mimicking the act of intercourse. NOTE - Can be applied to animals.

Usage: Dog's at it again, thrutching my leg last night.

Definition #3:
The name given to the "pressure" applied to the internal muscles required to push out a turd.

Usage: That curry had me thrutching like fuck the next day.
Usage: I thrutched so hard I nearly popped my grapes.
Usage: A night with big Jake left Wendy with no requirement to thrutch on her next visit to the lavatory.

Definition #4:
Description of awkward and strenuous moves, usually up a crack or chimney, when the climber feels like she is going to fall out and has to resort to whatever moves possible to keep on the rock. Another use is thrutching.

Usage: After getting up the Crack of Fear you remark, “Wow buddy, I didn’t think I was gonna get up that off-width section—it was a total thrutch!”

Definition #5:
thrutch (thruch) slang v. To hop the flagged foot while trying to weigh the standing foot; usually performed 'cause the standing foot is pure shit or, most likely, the hand holds are more so; the act of thrutching as opposed to scumming (to slide the flagged foot) [<Amer.].

Usage: he/she thrutched his/her foot.