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by Boris Bojanovic
Kettlebells are becoming quite a popular tool for fitness enthusiasts in Australia. Even though they are an old form of training, with a 300 year history in Russia, it is only now that kettlebells are reaching exercise physiology researchers’ labs. This is probably due to the loads of anecdotal evidence for the benefits of kettlebell training from its growing popularity.
Dr Stuart McGill of The University of Waterloo in Ontario Canada, a world authority on lower back pain prevention recently undertook a study to quantify the effects kettlebell training. He analysed muscle activation and spine loading in the single arm swing.
The study results concluded what we intuitively know about the kettlebell swing. That it is a hip hinge squat pattern where the gluteal muscles are significantly activated to drive the kettlebell up. And this activation is preceeded by lower back extensor & abdominal muscle activity to keep the integrity of the spine & transfer hip drive to the kettlebell.
McGill also found that the swing’s ballistic nature creates rapid pulses of muscle activity & that there is very little eccentric component because gravity assists in lowering the bell. This may be why we find that swings don’t produce as much soreness as, say a stiff leg deadlift. This also makes the kettlebell swing a great posterior chain power development exercise.
The forces on the spine were found to be modest & “probably not of clinical significance for the spine”. The one unique effect of kettlebell swings on the spine compared to squats & deadlifts is due to the inertia & centrifugal forces of the swing. This unique posterior shear force on the lower back may explain why some people who can squat & deadlift without complaint may get discomfort from swings. McGill goes on to say that lower back pain comes from movement flaws & correct kettlebell instruction for hip hinge & neutral spine, with maybe an intermediate exercise such as the kettlebell Romanian deadlift will prepare the spine for this unique feature of kettlebell swings.
Lastly, a feature of kettlebell swings which relates to our anecdotal evidence of people reporting reduced lower back pain after a period of kettlebell training is related to the rapid contraction-relaxation cycles of swings. McGill believes that this rapid switching from activation to relaxation acts to flush the lower back muscles with blood, clearing metabolites & therefore reducing lower back pain.
There you have it, new research into kettlebells has proven what we have intuitively known about kettlebell training. The swing is a hip dominant exercise which provides great power development opportunities, different to squatting & deadlifting. While it may cause discomfort in those experienced in traditional lifts but new to kettlebells, as with any new skill, proper instruction & progression are required. The dynamic nature of swings may even aid in lower back pain reduction by clearing metabolites in lower back muscles.
McGill, SM, & 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