Stemming from my recent forays into research on the risks and benefits associated with exercise using Kettlebells, I was asked by a fellow coach for my thoughts on safety considerations involved in the Kettlebell Swing, and its potential benefits.

As with most exercises, the inclusion of which into a program is obviously individual and end-goal specific.
That said there exists little evidence on resulting joint loads of the kettlebell swing (KS), despite the re-emergence of kettlebell use in recent years as a popular training modality. This makes it difficult to gauge specifically who may be at risk by performing the exercise.

In this study (1), researchers set out to quantify spine loading during various kettlebell swings and carries, and provide further insight into the mixed anecdotal response experienced by lifters. Some individuals have attributed the KS with being inflammatory of lower back conditions, whilst barbell lifts involving more of an axial load vector are accomplished pain free. Others have attributed the KS with facilitating the rehabilitation of a lower back injury and enhancing athleticism.

Focusing on the swing portion of the study, electromyography, ground reaction forces and 3D kinematic data was obtained during exercises using a 16 kg kettlebell, performed by seven male subjects, excluding any participants reporting with previous or current low back pain or injury.

It was shown that as the swing progressed from beginning, through its arc towards the top of the movement, low back extensor activation peaked first at about 50% MVC. This was followed by the rectus abdominis and external oblique at under 20% MVC, over 30% MVC in the internal oblique, and finally the gluteal muscles experiencing the highest activation levels at 76% MVC at 57% of the movement.

Spinal loading was highest at the beginning of the swing (461 N of posterior shear and 3,195 N of compression) and reduced significantly at arks end (156 N of shear and 1903 N of compression).

Researchers also found that the swing elicits a hip-hinge squat pattern accompanied by rapid contraction-relaxation cycles of muscles of the posterior chain and abdominals of high magnitudes, occurring over half-second intervals.
Further, it appears the effort is mostly concentric with gravity mitigating the eccentric component of the movement.

Also, due to the inertial component to the lift, forces required to accelerate the kettlebell through its curve produce relatively high posterior shear to compression force ratios, which is a unique loading pattern compared to traditional axial loaded lifts, offering insight into the mixed anecdotal evidence provided by lifters as mentioned above (McGill and Marshall, 2012)(1).

It appears then that individuals considering incorporating the KS into a training regime must first display adequate spine stability in shear mode and posterior shear loading tolerance if the unique training effect of the exercise is to be enjoyed safely.

In the video below, Joe Sansalone of Optimum Performance Training Institute displays flawless double KS technique.

In the picture below, extremely poor KS technique is illustrated.

In one clinical trial conducted on workers reporting neck/shoulder and low back pain researchers observed diminished pain in participants after a progressive KS-based training intervention with increased torso extensor strength, although aerobic fitness remained unchanged (Jay et al. 2011)(2).

In contrast, Farrar et al. 2010(3) concluded that ”continuous kettlebell swings can impart a metabolic challenge of sufficient intensity to increase Vo2max.”
Subjects were instructed to perform as many self-paced two-handed swings as possible in a 12 minute time frame with a 16kg kettlebell. Heart rate and Vo2 were monitored during the exercise. Average maximum HR and Vo2 achieved were 87 and 65% respectively providing a greater cardiorespiratory challenge than has been noted with traditional circuit weight training.

Some studies support the use of KS’s as a viable surrogate cardiovascular training tool whilst others have reported insufficient markers of an aerobic effect to be considered a useful alternative.
Methodological variances between studies that attempt to quantify the metabolic demand of KS’s may explain the polarity of results (Hulsey et al. 2012)(4).
Specific variances may include load, intensity, duration, frequency, and subject characteristics.

In this study(5), researchers sought to determine the effect that a 6 week bi-weekly KS program had on established maximum (half squat-HS1RM) and explosive (vertical jump height-VJH) strength compared to the effects of jump squat power training (JS-shown to improve 1RM and VJH). Both maximum and explosive strength measures improved with no significant differences between the KS and JS training interventions (Lake and Lauder, 2012)(5).

I also found this study (6) interesting in that although Olympic Lifts were found to be superior to kettlebell training at increasing vertical jump and squat strength, both were effective (Otto III et al. 2012)(6).

Although KS’s were performed by the kettlebell group, they were also assigned kettlebell goblet squats therefore results cannot be isolated to the KS. There was also discrepancy between the loading used by the kettlebell group vs the weightlifting group, 16kg and 80% 1RM respectively. This provides the weightlifting group with a distinct advantage.

It should also be noted when comparing KS’s to the squat, VJ or olympic lifts that the KS is characterised by more of an axial/anteroposterior load vector while an axial vector predominates the latter. This is an important distinction when making comparisons of performance test outcomes.

Practical applications

It appears that there is a large mechanical demand during the KS (Lake and Lauder, 2011)(7) that suggests it can provide numerous unique training benefits, making it a viable alternative to more traditional exercise modalities. However, the resulting shear to compression load ratios on the lumbar spine unique to the KS may for some individuals contraindicated prove.
For this reason, shear stability and posterior shear loading tolerance is required prior to performing the KS without provocation.

”You’ve got to be rich to have a swing like that.”
– Bob Hope

DJ

References:

1. McGill SM, Marshall LW. Kettlebell swing, snatch, and bottom-up carry: Back and hip muscle activation, and low back loads. J Strength Cond Res 26(1): 16–27, 2012.

2. Jay K, Frisch D, Hansen K, Zebis MK, Andersen CH, Mortensen OS, and Andersen LL. Kettlebell training for musculoskeletal health: A randomized controlled trial. Scand J Work, Environ Health, ahead of print, 2010.

3. Farrar RE, Mayhew JL, and Koch AJ. Oxygen cost of kettlebell swings. J Strength Cond Res 24(4): 1034–1036, 2010.

4. Hulsey CR, Soto DT, Koch AJ, and Mayhew JL. Comparison of kettlebell swings and treadmill running at equivalent rating of perceived exertion values. J Strength Cond Res 26(5): 1203–1207, 2012

5. Lake J, Lauder MA. Kettlebell swing training improves maximal and explosive strength. J Strength Cond Res, ahead of print, 2012 May 10.

6. Otto III WH, Coburn JW, Brown LE, and Spiering BA. Effects of weightlifting vs. kettlebell training on vertical jump, strength, and body composition. J Strength Cond Res 26(5): 1199–1202, 2012

7. Lake J, Lauder MA. Mechanical demands of kettlebell swing exercise. J Strength Cond Res, ahead of print, 2011 Dec 28: