This shouldn’t come as much of a surprise…The weightlifting group lifted much heavier weights during this study. For example, the weightlifting group was lifting 80% of their 1RM – roughly 106kg – during back squats, while the kettlebell group was lifting only 16kg during goblet squats, which comes out to about 12% of their 1RM.

While the authors here used the same protocol for progressive overload, i.e. they didn’t increase the weight for either group, just the fact that the weightlifting group was lifting much more weight partly explains the discrepancies there. Again, the same conclusion mentioned in the second annotation was reinforced here: the most efficient way to load the body with weight is with a barbell.

What does this mean?

Kettlebell training certainly has a place in some programs, depending on the individual’s goals, training experience, and time commitment. However, if you are training for pure strength, traditional weightlifting is the only way to go!

As per the vertical jump increases from both groups (italics mine):

To our knowledge, this is the first study to document the effectiveness of kettlebell training in improving performance during a lower-body power movement…It is well known that weightlifting can increase vertical jump performance (3,4,8), but it appears that kettlebell training can be just as effective in improving jumping performance. This might be explained by the similar movements of powerful ankle, knee, and hip extension done as quickly as possible while performing various kettlebell exercises.

For back squat:

As with the vertical jump, this is the first study to show that kettlebell training has the ability to increase 1RM strength, despite the emphasis of kettlebell training on explosiveness and the speed of movement rather than strength development.

The weightlifting group saw larger increases across the board, but:

Only the differences in strength were statistically significant…

So if we look at the table in the previous note, we see the pre- and post-test totals for the back squat maximum:

• Weightlifting: before = 133.08; after = 151.15
• Kettlebell training: before = 124.24; after = 129.82

The effect size was 18.7 kg and 5.58 kg for weightlifting and kettlebell training, respectively. Which comes out to 13.6% and 4.5% increases, respectively.

The weightlifting group used a certified weightlifting bar and Olympic plates. More specifically, they performed the lifts with 80% of their individual one-repetition maximum.

At the moment, there are very few studies that have looked at the performance enhancing effects of kettlebell training. One reason for this is the fact that fitness fads are constantly rising and falling, so physiologists can’t be bothered to test every single fad. However, considering the kettlebell’s history, it’s obviously more than just a fad.

As this article mentions in its introduction:

Coaches may have an interest in using kettlebells; if space is limited, there is a lack of funding for Olympic bars or weights, or to assist athletes who have never lifted weights in gaining a foundation in the fundamentals of similar movements relating to strength and power (squat, press, clean and jerk, snatch).

Thus, the point of this study isn’t to come to a conclusion on whether kettlebell or barbell training is better – which is highly individual – but to look at what kind of performance improvements can be expected if one chose to use kettlebells rather than barbells for some extended period.

For the most part, both of these techniques deserve a place in your routine, for different reasons.

Just to be clear, the two sessions per week focused on the same movement and a corresponding sets/reps scheme. For example:

• Week 1 = Kettlebell swings or high pull, for 3 sets of 6 reps.
• Week 2 = Accelerated swings or power clean, for 4 sets of 4 reps.
• Week 3 = Goblet squats or back squats, for 4 sets of 6 reps.

Etc..

As far as progressive overload, which is needed to see any improvements:

Progressive overload was achieved through a combination of increased volume and an emphasis on the technique and speed of movement.

This goes for both the weightlifting and kettlebell groups.