McGill & Marshall (2011), did a kinematics analysis of some of the basic movements of kettlebell work. Using a 16kg kettlebell on 7 male weightlifters and 1 kettle instructor, they found that the kettlebell swing and snatch movements require a hip-hinge squatting movement that activates 50% MVC of low back extensors and 80% MVC gluteal muscles.
What was quite interesting was the fact that kettlebell swings include a posterior shear element along the lumbar spine. Most exercise (squats, deadlifts and their variants) generally put an anterior shear on the spine- thus the kettlebell swing can have an almost prehab effect, ensuring that the spine is returned to a more neutral posture. Many athletes have reported that kettlebell swings done in conjunction with squats or deadlifts minimizes the discomfort they feel in their backs while a few report increased pain. This new analysis explains why. Some individuals are posteriorly loaded the posterior shear is painful while most of us are anteriorly loaded and shearing posteriorly will only help us.