The Air Runner and the Road Reward Two Different Runners

 I see a lot of running coaches in the CrossFit space treating running as one skill that looks the same everywhere. Running inside of CrossFit carries a lot more nuance than that, and understanding those details can help athletes improve dramatically on the leaderboard. 

My job as a coach is to simplify things so an athlete can succeed with as little friction as possible. A simple cue works best when it comes from a coach who knows the athlete and has earned the trust behind it, which is why I'm slower to hand out quick answers to athletes I haven't worked with. This post lays out the reasoning that sits underneath those cues.

We run two different modalities in CrossFit

In CrossFit we run in the open world on concrete, dirt, and trail, and we run on an air runner. They look like the same test on paper, and they reward different athletes and different mechanics. Even within the open world, we have a major change in terrain and technique that has a lot of changes, but for today we are going to think about this as flat running. The thing that is interesting to me is how much changing the running environment changes who performs best. 

Why the air runner favors bigger athletes

In general, heavier and bigger athletes have the advantage on an air runner, and there are three reasons for it.

The belt rewards force. The air runner is a belt you are actively pulling. Think about the flywheel on a C2 rower or bike and how heavier athletes tend to outperform lighter athletes on those machines. Similar to those machines, a heavier athlete can put more force into the belt, and because they aren't physically propelling their own body across the ground, that force becomes a real competitive advantage. Running on the air runner is closer to a pure strength event than the pure running we think of in track and field, which is more of a relative strength test. 

The impact is lower. A treadmill is much more gentle on the body from a force acceptance standpoint. One of the things that makes smaller athletes better runners on the road is that every foot strike costs them less, because they have less body mass going into the ground. The air runner lowers that stress for everyone, which hands the bigger athlete back a piece of what the road normally takes from them.

Air resistance disappears. Outside, it costs more to push a larger frame through the air, especially on a windy day. Although you can argue that this is negligible at most CrossFit distances, once an event includes a 5K or an 8K, like we see at more and more competitions these days, it starts to show up in performance.

There is nuance here. The distances we run in CrossFit tend to favor taller athletes, and taller athletes are usually the bigger ones, so nobody can say exactly how far the treadmill tilts the field. Smaller athletes can also make up ground in other ways, and I'll get into those in later posts.

Each surface rewards a different foot strike

In my observation, almost every good road runner is at least a solid runner on the air runner. Plenty of athletes who are good on the air runner struggle on the road, and the reason is foot strike relative to the center of mass.

The most common fault I see in CrossFit road running is an overreaching stride. The curved deck of the air runner rewards this fault. The further up the curve your foot lands, the more momentum you build for free, because you are placing mass at the top of the slope and letting gravity help pull the slats down.

Take that same overreach onto pavement and it creates a horizontal force that pushes back against you. You then have to overcome that force on every stride to keep your momentum going forward, and over the thousands of strides in a race that becomes very costly. Essentially the same thing that gives you a huge acceleration on the air runner is now creating a braking force against you when on the road. 

The athlete who lands with a more vertical shin on the road keeps their forward horizontal momentum moving positively. They get to use bounding mechanics to their advantage, which is a far more passive use of energy than a hip driven, muscular stride that has to overcome then produce force on every step. That shows up as better running economy, and it holds in both mixed modal and single modality running.

Heat costs bigger athletes more outside

Generally speaking, the heavier an athlete is, the harder it is for them to dissipate heat. Muscle mass is a huge generator of heat and the bigger the frame, the more of it there is. Most indoor venues sit under 70 degrees, so the demand to shed heat stays relatively low compared to the outdoor competitions that land in the hot part of the year. In addition to ambient temperature, radiant heat from sunlight hits a bigger athlete much harder than a smaller one because there is more surface area to heat. 

Heat tolerance varies person by person, and there are big athletes who handle heat better than small athletes. On the aggregate, the relative impact of heat tends to push outdoor running in favor of smaller athletes. 

What this means for your training

Understanding these differences tells you how much of your training currency to spend on each kind of running. It also lets an athlete with adequate training volume and intention change how they run based on the environment in front of them, and those athletes improve their placement consistently because of it.

On the road, intelligent runners do three things:

• They draft when they are in a pack.
• They do whatever they can to manage their heat.
• They land under their body with a vertical shin instead of in front. 

On the air runner, drafting can't happen, heat management is done by the environment and smart athletes overreach with intention so they create as much pull on the belt as possible.

What comes next

This is the starting point. Over the next handful of months I'll dig into the technical side, along with the practical programming side. Running is something we can change, and improving it carries straight into how you perform in the sport. 

If running is the part of CrossFit you dread

If you are a CrossFitter who loses places every time a run shows up, you have more room to improve than you think. Most of that room comes from knowing which kind of running you are training for and matching your mechanics and your training to it.

Apply for coaching here and tell me where your running breaks down. I review every application personally, and it starts a conversation about where you are and where you want to go. From there we figure out which of these pieces applies to you and build your training around it.