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Kettlebell Research Update
Len Kravitz, Ph.D.

Kettlebell training is growing in popularity as an alternative system of training for musculoskeletal fitness. The total body approach of this training method may also improve aspects of cardiovascular health. Although the use of this kettlebell (KB) exercise appears to be increasing habitually with personal trainers, the experimental research on this type of training has been limited up to this point. This column updates IFJ readers with recent peer-review research on KB training.

Study 1) Metabolic demand of kettlebell training
Hulsey, C.R. Soto, D.T., Koch, A.J, and Mayhew, J.L. (2012). Comparison of kettlebell swings and treadmill running at equivalent rating of perceived exertion values. Journal of Strength and Conditioning Research, 26(5), 1203-1207.
Experimental Question
The two-handed KB swing is generally viewed as a foundational training approach for KB training. It is not known whether the metabolic demands of this exercise performed continuously may elicit an energy cost that will positively improve cardiorespiratory fitness. Therefore, the purpose of this study was to compare the metabolic demand of KB swings to treadmill running at equivalent ratings of perceived exertion (i.e., subjective assessments of exercise intensity).
Thirteen subjects (11 male, 2 female, ave. age=21.4, ave. height= 69 inches, ave. wt=170 lbs, ave. BMI=23.5) volunteered for this study. Subjects were deemed moderately trained and had no KB experience. Prior to testing all subjects were familiarized with the KB 2-handed swing exercise by a certified KB instructor.
Study Procedures
In the fist experimental trial subjects performed 10 minutes of KB 2-handed swings alternating 35-second swing bouts followed immediately by 25 seconds of rest, where no exercise was completed. Men used a 16-kg KB and the two women in the study used an 8-kg KB. Subjects were encouraged to maintain a steady swing count, which averaged 22-25 swings per minute for all subjects. A certified KB instructor gave continuous feedback helping clients maintain correct swing execution and posture during their exercise trials. After a 48-hour rest period the subjects returned to the testing lab and completed a 10-minute treadmill run at an equivalent subjective intensity (i.e., rating of perceived exertion of 15.3-15.5 on a 6 to 20 scale) as the subjects KB swing trial. An automated metabolic gas analysis system that is commonly used in exercise studies measured oxygen consumption and kilocalorie expenditure. The final 7 minutes of the each work bout were used for data analysis.

Results and Discussion
Table 1 compares key cardiovascular and metabolic values obtained in this investigation. At an equivalent subjective rating of perceived exertion there was no significant difference in heart rate. Oxygen consumption and calorie expenditure were significantly higher for treadmill running as compared to KB swings. However, it should be noted that the subjects completed both 10-minute bouts of exercise above 85% of their age-predicted maximum heart rate. Thus, KB swings, albeit for only 10-minutes in this investigation, did elicit a physiological response necessary for improving cardiorespiratory fitness. The major unanswered question of this study is what is the optimal KB workout duration and weekly frequency necessary to obtain a meaningful improvement in cardiorespiratory fitness. Further research is needed to answer this question. However, the kilocalorie expenditure (375 kilocalories) obtained from this study suggests KB training is a viable training modality for facilitation of a weight loss program.

Table 1. Cardiovascular and Metabolic Variables for Treadmill Running and Kettlebell Swings
Variable Treadmill Running Kettlebell Swings
Heart Rate (b/min): 177± 11 vs 180±12
VO2 (ml/kg/min): 46.7±7.3 vs 34.1±4.7
Kcals/min: 17.1±3.7 vs 12.5±2.5
Total Kcals: 512±111 vs 375±76

Study 2) Effect of kettlebell training on strength, vertical jump and body composition
Otto, W.H. III, Coburn, J.W., Brown, L.E., and Spiering, B.A. (2012). Effects of weightlifting vs. kettlebell training on vertical jump, strength, and body composition. Journal of Strength and Conditioning Research, 26(5), 1199-1202.
Experimental Question
Previous research has demonstrated that weightlifting exercises may improve vertical jump ability in athletes and recreational enthusiasts. In particular the snatch, clean and jerk and other explosive weightlifting exercises seem to resemble the explosive movement patterns of a vertical jump. KB training may be a viable exercise option for developing similar performance characteristics, yet there is no research in this area. Therefore, the purpose of this study was to compare the effects of 6 weeks of weightlifting versus KB training on strength, power and body composition.
Thirty healthy males (ave. age=23, ave. height= 69 inches, ave. wt=176 lbs, ave. BMI=26.5) who had one year of resistance training experience (but no KB training) volunteered to participate in this study. Subjects were randomly assigned to either the weightlifting or KB training groups. All subjects attended 2-3 exercise sessions during the week prior to the start of the study to learn the correct execution of the weightlifting or KB exercises. Subjects completed a pre-test and post-test of experimental variables (described below) before and after 6 weeks of training. Each subject trained twice a week with at least 72 hours between training sessions. Subjects were encouraged to maintain their normal dietary lifestyle during the six-week training period.

Study Testing Procedures
Vertical jump was assessed with a scientific testing vertical jump apparatus (i.e., EPIC Jump Station) with the best of 3 trials used for analysis. A one repetition maximum was employed to test maximum back squat and power clean ability following established testing guidelines. A 3-site skinfold for chest, abdomen and thigh was used to asses body composition.

Kettlebell and Resistance Training Procedures
Participants used a 16-kg KB and completed KB swings, accelerated KB swings, and goblet squats that were progressively increased in volume (number of sets) during he course of the 6 weeks. Emphasis was placed on proper form and technique in conjunction with an appropriate speed of movement. The weightlifting group performed high pulls, power cleans and back squats in a linear periodization model that attempted to replicate the number of sets and reps of the KB swings during the 6-week study. Although the researchers attempted to match the volume (reps x sets) of exercises performed with both training groups, the loads of the weightlifting group were heavier and thus represented a limitation to the study findings.

Results and Discussion
The KB and resistance training group both equally improved vertical jump (about 2%) ability after the 12 training sessions in weeks. The KB group significantly increased the power clean performance by 4.2% as compared to a 9% increase observed with the weightlifting group. With the back squat both groups showed significant improvements with greater gains being observed with the weightlifting group (14% increase) as compared to the KB group (4%). This may have been expected since heavier loads were performed on this exercise with the weightlifting group. There were no changes in percent body fat for either group during the 6 weeks of training. The findings of this study clearly show the potential power and strength benefits of KB training as an alternative to traditional resistance training methods.

Question: Is Kettlebell Training Safe for the Spine?
McGill and Marshall (2012) completed the first and only biomechanical study that has attempted to quantify spine loading during various KB exercises. Electromyography, ground reaction forces, and 3D kinematic data were recorded during exercises using a 16-kg KB with 7 male subjects. The KB swing (regardless of style of swing or snatch) appears to create a hip-hinge squat movement pattern together with patterns of rapid muscle activation-relaxation cycles that elicit considerable magnitudes of load on the spine. For this reason, this unique exercise may be very appropriate for some exercise programs emphasizing posterior power development about the hip. In contrast, the KB swing also appears to result in unique compression and shear load ratios in the lumbar spine that may explain the discomfort felt by some people in the lower backs, who otherwise tolerate very heavy loads. The message for personal trainers from this research is that KB training offers several unique training opportunities. However, the large shear to compression load ratio on the lumbar spine created during KB swing exercises suggest that this training approach may be contraindicated for some individuals. Personal trainers who are interested in introducing KB training to clients should follow careful progressive overload training procedures to ensure safe and effective training outcomes.
Additional Reference:
McGill, S.M. and Marshall, L.W. (2012). Kettlebell swing, snatch and bottoms-up carry: Back and hip muscle activation, motion, and low back loads. Journal of Strength and Conditioning Research, 26(1), 16-27