The Kettlebell Mile is the product of a two-decade long search for a way to simultaneously train strength and aerobic capacity. It seems so obvious now, but the best ideas are seen as such only in retrospect. I had much learning and tinkering to do first but finally, the science and my experience (and that of others) converged around this simple idea. What follows is a brief description of that process.
I have been interested in load carriage fitness for more than twenty years. It started in 1997, when I attended the Marine Corps Mountain Warfare Training Center’s Wilderness Medicine course. The training center is at an altitude of about 8,000 feet and terrain in the area rises to above 10,000 feet. We ran in the mountains every morning, and then packed up a bunch of climbing gear along with medical supplies and survival items, and marched uphill for several miles to the training area with our loaded backpacks. I just happened to be a middle-of-the-pack guy for both the runs and the rucks, so I was able to notice something interesting. The guys who were out front on the runs were off the back on the rucks and vice versa. The skinny runners were hurting as soon as you put a pack on them but the six-foot plus big guys who suffered on the runs were crushing everybody on the rucks. One big, tall guy was dropped in the first half mile on all of the runs. You would assume from his performance on the runs that he showed up for the course in poor shape. However, he was up front for the rucks, effortlessly pushing the pace. I kept expecting to see him drop, but he didn’t. This whole phenomenon was quite a surprise for me. I knew that something interesting was happening so from that point on, I started to pay attention to the research on load bearing marches.
My first clue about what was going on was from my own perceptions of the difference between the rucks and the runs. My limiter on the run was a sense of whole-body fatigue and breathlessness. However, on the rucks, I wasn’t completely out of breath. The issue was the tremendous amount of fatigue in my glutes and especially my hamstrings. I did not have the muscular power to push the pace any faster, though I still had some cardiovascular reserve. The effort during the ruck was obviously aerobic due to the duration (over two hours) and the fact that my heart rate and breathing were significantly elevated. However, my performance was limited by muscular fatigue, not by my cardiovascular capacity. Was this why the big guys did so well on the rucks compared to the runs?
When I finished the course, I began to dig into the research literature on load carriage. Fortunately, the U. S. Army has sponsored lots of research on the topic. There were some interesting, and somewhat surprising findings among the research papers. Researchers found that when ruck loads exceed 40kg (typical military combat load):
- Unloaded run performance does not seem to be related to ruck performance.
- Run training alone has little impact on ruck performance.
- Strength training alone improves ruck performance.
Let’s pause to contemplate these findings for a minute. So far, the research seems to indicate that strength is more important than cardiovascular fitness for heavy ruck performance. If you have to choose between running and strength training, you should choose strength training to improve your ruck performance for a typical military combat load. There were a couple of other interesting findings though.
- Strength training combined with a running program resulted in greater ruck performance than strength training alone (or running alone).
- Heavy ruck training transferred performance benefits to light (but longer) ruck events but not vice versa.
- If participants engage in a strength training program and a run training program, there is little benefit from engaging in ruck training more than once per week.
The picture that began to emerge was that at heavier loads (i.e., greater than 40kg), strength is favored over aerobic capacity. However, it is obvious that as loads get lighter, you will reach a point where aerobic capacity is favored over strength (i.e., at zero load). Somewhere in the middle we should theoretically be able to find a crossover point where strength and aerobic capacity are equally favored in determining ruck performance. If we could test, and train near that crossover point, we could test and build strength and aerobic capacity simultaneously with one simple task.
As a scientist and a consultant to the U. S. Navy and Marine Corps, I was interested in finding that crossover point because it might be a simpler, more effective test of military fitness than running, sit-ups, pushups, and pullups commonly employed by the services. It could provide a single, simple metric to determine if a training program was producing “tactical fitness.”
I never had the chance to formally test these ideas during my career, but I had plenty of chances to do some informal testing while serving as the staff exercise physiologist at the U. S. Naval Academy. I had a chance to work with many midshipmen who had load carriage task requirements (Infantry Skills Team, Special Operations Team, USMC TBS, SEAL Screener, EOD Screener, etc.). Though the U. S. Army recommends that soldiers never run with a loaded pack, the reality is that this is common, and even necessary for some screening events. It became obvious that run gait was severely hampered when loads exceed about 35% of bodyweight. Most people could only shuffle along with heavier loads. On the other hand, loads of less than 20% of bodyweight seemed to be relatively easy, even for distances of four to five miles. So, it seemed as though a good, moderate load that was challenging, but tolerable for reasonable distances and at a reasonable pace (fast walk to a slow jog) was between 20% and 35% of bodyweight.
Around this time my interest in load carriage began to intersect with my other interest, run gait analysis. I was observing and filming athletes running on the treadmill during VO2 max testing in my lab. The most consistent run gait flaw I observed was nonsupport side hip drop with run cross over gait. This happens when the gluteus medius and gluteus maximus (along with all of the abdominal trunk musculature) fail to stabilize the hip when the foot impacts the ground. This results in the hip moving outwards laterally (on the foot/ground contact side) and excessive hip drop (on the other side).
To compensate for poor hip stability, runners adopt a cross over gait style. To envision run crossover gait imagine if we drew a chalk line on the treadmill belt (I actually did this), and asked runners to keep the line centered as they ran. In a “normal” gait, the second toe (the one next to the big toe) would not cross over the line. In crossover gait, the second toe, and often, the whole foot crosses over the line on both feet, so they are crossing over the line with each step. The crossover is happening because the hip is moving out laterally. It all starts with poor hip stability.
As a result of this insight, I started working with these runners to train hip stabilization. One obvious choice was to load a correct gait pattern so that we could build hip stability and strength. We started with loaded backpacks and found that they could feel fatigue in the gluteus medius and maximus when they concentrated on stabilizing their hips during the crossover gait drill (walking or running along a line on the road without stepping over the line with either foot), so I knew we were on the right track.
I made one small adjustment that seemed to have a very positive impact. Because I was working with runners, not infantry soldiers, I switched from a loaded backpack to a kettlebell held in the suitcase carry position. Because this is a single sided carry, much more trunk musculature effort was required to carry a similar load. In one move we were addressing most of what was causing the flawed run gait in most of the runners. Unlike traditional loaded carries, which are usually 10-50 yards, we wanted longer distances because we were trying to build both strength and endurance so that we could improve hip stability and run gait. As a bonus, it is safer than running with a similar load because when you fatigue you can simply drop the kettlebell and rest. You can’t do that with a backpack. Also, the load seems to be cushioned more in the suitcase carry position than when it is loaded directly on the spine with a backpack.
After some trial-and-error, we settled on a simple session of moving on foot, carrying a kettlebell for one mile—the Kettlebell Mile. It was easiest to use the common sizes, 16kg for ladies and 24kg for gentlemen. That generally put us in the 20% to 30% of bodyweight range. As you would expect, skinny runners with little strength and big, strong guys who are poor runners generally do not do as well as good runners who also have some strength or big, strong guys who can also run. We seemed to have stumbled on a load and distance that is in the vicinity of the aforementioned crossover point where strength and aerobic power are equally important and because of that we would expect a runner with a bit of a strength base and a weightlifter with a bit of a run base to do equally well. Performance on this simple test seems to be a good indicator of the kind of fitness that first puzzled me at the Marine Corps Mountain Warfare Training Center years earlier. It is also a great training session for runners (to train hip stability) and those who are looking for that “middle of the road” fitness, somewhere between strength and endurance (i.e., tactical athletes).
Is this a test or a training session? It can be both or either. Consider what it would take to do well at this simple event. If, for example, a person can cover a mile in nine minutes with the prescribed kettlebell load, what kind of “what the heck” effects might you expect? Lots of good things probably. If doing this as a training session, it is best done, at most, once per week, as with rucking, when combined with a strength training and running program. Use simple progressive overload by increasing either the distance or the load initially, until you can complete a mile with the prescribed weight. Then start to work on speed. As a test it can be done periodically to gauge progress. I also think it has lots of potential as a competitive event.
Most people are going to walk it initially. A fast walk for most people is going to be at about 4 miles per hour or 15 minutes per mile (really moving). So, if a person can keep moving, switching hands on the go, they can complete it in 15 minutes while walking fast. Those who can jog with it might manage 11-13 minutes. 9-11 minutes is very good. Under 9 minutes is very, very good.
Performing the Kettlebell Mile is simple. Find a measured distance that is relatively flat. It can be a track, an out-and-back course, or a point-to-point mile. Anything works. Simply carry the kettlebell in the suitcase carry position, switching hands and stopping as often as you want (but the clock keeps running). Cover the distance as fast as you can. You can walk, jog, or run. No gloves are allowed but you can use chalk. I like to hook a chalk bag to my shorts with a carabiner and I also carry a sweat rag tucked in my shorts for when it is really hot.
I’ve gotten lots of feedback from people who have tried the Kettlebell Mile and the general consensus is that it just feels right. It seems to be the right load, distance, and type of effort. Much like the first time I tried Simple & Sinister, the first time I tried the Kettlebell Mile, I knew I was on to something. In his bestselling book, Christopher McDougall argues that we were born to run. I would argue that we are also born to carry things. This is a simple, primal move. But don’t take my word for it. Grab a kettlebell and give it a shot and see if it feels right for you.