I've been wondering if Torso / Back twisting exercises (like twisting from side to side, with weight or without weight) can be harmful to the back. Mainly, if you'd have a herniated disc - would a twisting exercise aggravate the condition? If you're healthy, could such exercise create an injury?

Exercise examples:

http://www.mmmglawblog.com/wp-content/uploads/2013/03/10.-Spine-Twist.jpg

http://urbanwired.com/health/wp-content/uploads/sites/2/2014/08/Kettlebell-Workouts-for-Russian-Twist.jpg

thanks!