The first Kettlebell study I've heard of

Here it is http://www.ncbi.nlm.nih.gov/pubmed/21997449
I only have access to the abstract but it's better than nothing.
The major points are:

It seems kettlebells load the spine in the opposite way to many lifts, this 'could' explain why they seem to help some lifters with back issue recover. So, they may not be the ideal for everyone's back problems, but could help other people (for now you won't know until you try I suppose, but my guess would be if you hurt your lower back doing traditional lifts, then kettlebells might help & they might also help the lower back for prehab - as some trainers have claimed for a while & suggested heavy lifters also include light KBs to 'ease the back'). So there you have it, the first KB study so far

The details are:

Quote :

J Strength Cond Res. 2012 Jan;26(1):16-27.
Kettlebell swing, snatch, and bottoms-up carry: back and hip muscle activation, motion, and low back loads.
McGill SM, Marshall LW.
Source

Spine Biomechanics Laboratories, Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada.
Abstract

McGill, SM, and Marshall, LW. Kettlebell swing, snatch, and bottoms-up carry: Back and hip muscle activation, motion, and low back loads. J Strength Cond Res 26(1): 16-27, 2012-The intent of this study was to quantify spine loading during different kettlebell swings and carries. No previously published studies of tissue loads during kettlebell exercises could be found. Given the popularity of kettlebells, this study was designed to provide an insight into the resulting joint loads. Seven male subjects participated in this investigation. In addition, a single case study of the kettlebell swing was performed on an accomplished kettlebell master. Electromyography, ground reaction forces (GRFs), and 3D kinematic data were recorded during exercises using a 16-kg kettlebell. These variables were input into an anatomically detailed biomechanical model that used normalized muscle activation; GRF; and spine, hip, and knee motion to calculate spine compression and shear loads. It was found that kettlebell swings create a hip-hinge squat pattern characterized by rapid muscle activation-relaxation cycles of substantial magnitudes (∼50% of a maximal voluntary contraction [MVC] for the low back extensors and 80% MVC for the gluteal muscles with a 16-kg kettlebell) resulting in about 3,200 N of low back compression. Abdominal muscular pulses together with the muscle bracing associated with carries create kettlebell-specific training opportunities. Some unique loading patterns discovered during the kettlebell swing included the posterior shear of the L4 vertebra on L5, which is opposite in polarity to a traditional lift. Thus, quantitative analysis provides an insight into why many individuals credit kettlebell swings with restoring and enhancing back health and function, although a few find that they irritate tissues.