Stand with the feet about shoulder width apart holding a barbell as you would for a back squat. Rotate at the trunk to one side, keeping the feet planted solidly on the floor, and rotate back the other direction.
 
Note that the barbell’s length creates a lot of momentum which will make stopping and changing directions much more difficult even at slow rotation speeds—be very conservative with how fast you rotate until you learn what speed you’re able to control.
 
Purpose
The standing barbell twist trains rotational strength and stamina for general trunk stability.  
 
Programming
The standing barbell twist should be performed for sets of 10-20.