The Journal of Strength & Conditioning Research recently released a study that compared the effects of six weeks of weightlifting plus traditional heavy resistance training exercises to kettlebell training. The study found that six weeks of weightlifting led to considerably greater improvements in strength compared to those who trained using only kettlebells.
Thirty healthy men were randomly assigned to either a weightlifting or kettlebell group, where they exercised twice a week for six weeks, using relatively comparable movements using the two different pieces of equipment (barbells and kettlebells).
A linear periodization model was used for training; at weeks 1–3 volume was 3 × 6 (kettlebell swings or high pull), 4 × 4 (accelerated swings or power clean), and 4 × 6 (goblet squats or back squats), respectively, and the volume increased during weeks 4–6 to 4 × 6, 6 × 4, and 4 × 6, respectively.
While neither method of training appeared to drastically affect the physical appearance of the participants, the study "indicated that short-term weightlifting and kettlebell training were effective in increasing strength and power."
And for those interested in building strength, "the gain in strength using weightlifting movements [high pull, back squat, power clean] was greater than that during kettlebell training." Interestingly, neither method was more effective than the other in terms of increasing the participants' vertical leap, despite the strength gains seen with weightlifting movements.
For the study, the exercises performed by the participants were all multijoint, full-body movements, which makes sense why the two pieces of strength training were compared this way.
While the study found barbell movements to be more effective in building strength, it didn't compare the exercise's effect on participants' metabolic conditioning. Additionally, it is generally difficult to find a kettlebell heavier than 100 pounds, so it's very likely that the kettlebell group was not given a 1:1 opportunity to "max out" to failure in the same way that the weightlifting group was. Kettlebells are often used at higher repetitions than barbells in workouts as well, so replicating the sets and repetitions between the two pieces of equipment might have heavily leaned the strength scales in the barbell's favor.
Do you use kettlebells and barbells in your strength training? Do you find one more effective than the other in building strength?