In a glute ham bench or similar, perform a back extension while rotating to one side. Rotate back to neutral as you return to the bottom and rotate the other direction in the next rep.
 
Purpose
The rotating back extension both trains the activation of the spinal extensors and strengthens their ability to extend the back, and addresses more of the lateral posterior trunk musculature that’s often overlooked.
 
Programming
Unweighted back extension rotations can be added once/week in addition to conventional extensions and other back work with 3-4 sets of 10-15 reps/side.


Variations
The tempo of the movement can be changed, and a pause in the extended position can be added.