I’ve written before that kettlebells are great for conditioning, but I haven’t really supported that. Not scientifically, at least, and it’s time I fixed that.
However, like almost everything with regard to kettlebells, the science is a little muddled. Part of that is due to design, but is that all there is?
Let’s take a look at see.
In one study, researchers compared kettlebell swings to treadmill running. They use Rate of Perceived Exertion (RPE) to try and balance the two modalities to create an even comparison. So what did they find?
This study indicated that when KB and TM exercises were matched for RPE, the subjects were likely to have higher oxygen consumption, work at a higher MET level, and burn more kilocalories per minute during TM running than during KB swings. However, according to American College of Sports Medicine (ACSM) standards (1,2), this KB routine could provide sufficient exercise stress to produce gains in aerobic capacity since the %HRmax exceeded 85% in most of the subjects. Therefore, on days when a subject wanted an alternative to TM running or stationary cycling, KB swings might be substituted to maintain cardiovascular training levels (7,8,17).
So treadmill running is superior, right?
Well, not necessarily. There are a couple of issues with this study that bears mentioning. One, of course, is that there were only 13 people involved in this study (11 male, 2 female). that introduces that “statistical noise” I mentioned a couple of days ago.
For another, this is how the study describes the participants: “The subjects were moderately trained but had no experience exercising with KBs.”
Now, keep in mind that RPE is subjective. Since none of the participants had been exposed to kettlebells before, how much of their RPE was due to physical exertion and how much was due to the technical demands?
It’s hard to say. After all, people start running in early childhood, so running on a treadmill will likely only be found demanding on the cardiovascular system as opposed to a kettlebell swing for someone who has never done one.
But that’s just speculation on my part.
Another study compared the kettlebell swing to the treadmill, this time focused on treadmill walking.
On that one, kettlebells faired a good bit better.
The hypothesis that a moderately intense KB protocol would produce metabolic responses similar to those produced by a brisk walking protocol was confirmed for V[Combining Dot Above]O2, RER, kcal·min−1, and BP in this study. Moreover, as hypothesized, KB elicited greater RPE than TM. However, contrary to our hypothesis, KB produced higher HR than TM exercise. The data collected in this study indicate that when regulated for frequency of work, a KB routine consisting of 2-hand swings, and sumo deadlifts will elicit similar metabolic responses to those from a moderate-intensity TM walking protocol designed for the improvement of aerobic fitness.
None of this really looks great for kettlebells. I mean, that study just had ten people–another tiny sample size–but that’s what we’re going to see in a lot of these, I’m afraid.
I mean, is the conditioning effect really that limited?
Maybe the issue isn’t the kettlebell, but the swing.
Another study looked at intensive kettlebell snatches in collegiate women’s soccer players. What it found was interesting.
The 21 women were divided into two groups, one training snatches and one as a control group using circuit weight training.
The median change for the KB and CWT groups was 2.1 and 0.15 ml·kg−1·min−1, respectively (Mann-Whitney U statistic = 58.0, p = 0.038); the increase in aerobic capacity in the KB group was significantly greater than the increase in the CWT group. Thus, kettlebells can be used as a training modality within a high-intensity interval training program to improve aerobic capacity in female collegiate soccer players.
In other words, the snatch held up.
Of course, this study has its own issues. For one, individuals weren’t randomly assigned, but that was for good reason, though. The researchers assigned people to the kettlebell group who showed proficiency with the snatch, a more technical exercise.
Another study, this one sponsored by the American Council on Exercise, found that the caloric requirements for the snatch–an indicator of just how intensive the exercise taxes your system–was akin to cross-country skiing uphill.
During the 20-minute workout, the average calorie burn was 272 calories, not counting additional calorie burn due to the substantial anaerobic effort.
“We estimated oxygen consumption and how many calories they were burning aerobically, and it was 13.6 calories per minute. But we also measured the blood lactate, so anaerobically they were burning another 6.6 calories per minute,” explains Porcari. “So they were burning at least 20.2 calories per minute, which is off the charts. That’s equivalent to running a 6-minute mile pace. The only other thing I could find that burns that many calories is crosscountry skiing up hill at a fast pace.”
Researchers credit the brisk calorie burning to the fact that the kettlebell snatch workout is a total-body movement that is also done very quickly due to the interval-training format. “We knew it would be extremely intense,” says Schnettler. “It’s a quick workout, and you do get a big bang for your buck in a very short amount of time.”
As for heart-rate data, the average HR during the kettlebell snatch workout was between 86 percent and 99 percent of the kettlebell HR max for all subjects (Figure 1). “The average heart rate was 93 [percent], but some people averaged, for the 20-minute workout, 99 percent of heart rate max,” says Porcari. “Anytime you’re using that much muscle effort, it’s going to be a vigorous workout.”
As for the V• O2 max, the treadmill V• O2 max was 23 percent higher (38.9 ml/kg/min vs. 31.6 ml/kg/min) than the V• O2 max attained during the kettlebell V• O2 max test (Table 1).
So while the max VO2 was higher with a treadmill, it was still a solid cardiovascular workout.
Yet a higher VO2 max may have had more to do with the type of training. This study used Tabata-style training to compare HIIT kettlebell training to sprint interval cycling (SIC) training.
A significant group effect, time effect, and group × time interaction were found for V[Combining Dot Above]O2, RER, and TV, with V[Combining Dot Above]O2 being higher and TV and RER being lower in the KB-HIIT compared with the SIC. Only a significant time effect and group × time interaction were found for f, VE, kcal·min−1, and HR. Additionally, total caloric expenditure was found to be significantly higher during the KB-HIIT. The results of this study suggest that KB-HIIT may be more attractive and sustainable than SIC and can be effective in stimulating cardiorespiratory and metabolic responses that could improve health and aerobic performance.
It’s far from the only study to show that superiority of Tabata training with a kettlebell (more on that another day). Granted, it has a very small sample size, but it’s still interesting. Especially since it’s far from the only study showing such a response.
So what we have is a case of kettlebells being effective training if used correctly. However, let’s be honest for a moment. Isn’t that true of anything?
The kettlebell swing is a great exercise, but at some point, we’re going to have to understand that just swinging a weight around is going to give us only so much in the way of gains. We’re going to have to step up the game a bit.
Sometimes, you have to work smarter if you want results.
After looking at a number of studies, it should be noted that kettlebells are an effective means of conditioning, regardless of how you use them.
Note that even the most critical studies showed that one could get cardiovascular benefits from kettlebell training. However, studies also show how much more effective Tabata-style training is than traditional training, which means that’s something we should all start incorporating into our efforts at some point.
At the end of the day, though, there appears to be scientific consensus that the kettlebell is fantastic for conditioning work.
Because of that, we can imply that it’s likely to be beneficial for weight loss, though that’s a subject we’ll delve more into another day.