It might seem like I’m being overly dramatic with the title, but the following two concepts are critical for understanding running form, or even human movement in general. With the rise in popularity of running form and the increase in running form guru’s that accompanies that, I it was a good time to share what I feel is the most important lesson. Why? Because if you change mechanics and don’t know what you’re doing, you are begging for an injury. As always, I’m deeply in debt to the master when it comes to this topic, Tom Tellez. The two key lessons to learn are:

What happens Active versus Passive The difference between Static movements and Dynamic movements.

What’s so important about these concepts? Well, quite frankly it’s what separates the knowledgeable from the quacks. It’s relatively easy to watch a lot of good people run and figure out in a general idea what good running form looks like. What’s harder is to figure out what the runners are actually doing to get to that point.

Passive vs. Active

The concept is relatively easy, but sometimes difficult to grasp with all the scientific type stuff, so I’ll try and keep it to a minimum. The idea is that in dynamic movements like running, things happen both actively and passively. It’s a little more complex than that, in that there is a large interaction between the two, but let’s stick with making it simple. By active, we mean that muscles have to be actively contracted to accomplish some task. For instance, in doing a bicep curl, we know that the muscles in the arm work together to lift whatever weight is in your hand. Essentially, it’s active if you’ve got to try and do it (even if it’s so ingrained that aren’t actually “thinking” about it to accomplish the task)

Passively is a little more complex. You can subdivide passive into passive mechanics, and reflexive. Passive mechanics are things like momentum or inertia, where it doesn’t matter really if it’s a human or not, objects will act in various ways. Think back to your High School Physics class for this stuff. Reflexive is exactly as it sounds. It’s those things that happen without you actively thinking or doing anything. It happens as a result of something else. The common example is the test where they tap right below your knee in the doctor’s office and your foot kicks out a little.

If we look at the various passive mechanisms we have in our body, you’ll see things like the stretch reflex. Which should essentially be thought of as a rubber band. The muscle-tendon unit is stretched and then snaps back really quickly. You’ve got the stretch shortening cycle, which basically means that if you stretch the muscle a bit before contacting, you’ll get a bigger power increase. The typical example is the calf muscle during any sort of hoping. When you hit the ground, the calf is stretched, storing energy, and then contracted as you push off. A practical example would be a counter-movement jump. If we were to measure jump height, what would you do? You’d start standing, then squat down and immediately explode upwards. If you instead squatted down, held it for a few seconds and then exploded upwards, you would not jump near as high because you didn’t take advantage of the SSC.

There are other largely passive mechanisms that aid us in running. We could look at the elastic energy storage and transference through the body that occurs when you strike the ground, or we could look at the interplay of the motion in the upper and lower body which can aid in movement and force production. But…those topics are for another post, as I don’t want this to become an all encompassing 20 page post. So we’ll focus on what I’ll call the big 3.

Passive applied to Running:

So what does this actually mean in terms of running? Well, part of the running stride is active, and part of it relies on passive stuff. If you are changing someone’s mechanics and you are trying to copy some other runner, and you change something that he is doing largely passively, then you just screwed yourself. Because now you’re using muscles you don’t need to, which increases the energy cost and increases potential injury likelihood. Let’s take a look at the running stride and help Identify what happens passively, or at least mostly passively.

Kicking your butt:

When athlete’s sprint or run pretty quickly, most have a high back kick where the foot folds up and almost hits their butt as it passes underneath them. This is a good thing because it increases the angular velocity of the lower leg. But we don’t get there by thinking about actively kicking ourselves in the butt…Why?

Because the reason the foot goes close to the butt is because of the inertial force that the thigh exerts on the lower leg. Once the thigh is extended as far back as it’s going to go, it then shoots forward (for reasons we’ll discuss shortly). Well, since the thigh and lower leg are linked, the thigh changes directions a tad “sooner” and moves faster (because it’s closer to the rotation point…the hip) then it has a profound effect on what the lower leg does. The thigh essentially “drags” the lower leg with it. The faster the thigh moves, the more it “drags” it. So what’s the effect that we see? The faster the thigh moves forward, the more the lower leg folds up to the butt. It’s simply an inertial force.

If you want to get creative and see it for yourself, get some sort of simple 2 link segment to mimic the upper and lower legs. I’ve used a longer metal hinge before. Just play around with it making sure to rotate the “upper” part of the hinge/linked system and see what the lower part does.

Okay, so we got that lesson? The thigh speed partially determines what the lower leg does. (I say partially because body lean, the angle of the hips (the joint which everything “rotates” around) also will influence it…but that’s for another post). So move the thigh forward faster right? Wrong!

Moving your thigh and lifting your knee:

The problem with trying to really move your thigh forward is that once again, it largely occurs passively. The stretch reflex at the hip plays a large role. As the thigh/hip complex moves back rapidly as you apply force to the ground, it creates a stretch reflex effect so that once extension is complete, the whole thigh shoots forward. As I’ve mentioned previously, it’s best thought of as a pulling a slingshot back and then letting it go. As you apply force to the ground and the hip extends/thigh moves back, you are essentially pulling the slingshot back. Once you extend far enough back, then you “let go” and the thigh shoots forward.

The best practical example of this is when you take patients who have spinal lesions, put them on a treadmill, and then manually force the thigh/hip to extend. If you extend the hip enough, then let go, the leg will “magically” come forward through the swing phase in a close approximation to walking (and the lower leg will fold up slightly due partly to the inertial force exerted by the thigh).

So, trying to move your thigh through the swing phase faster is a foolish thing to do. It’s trying to make something that is largely “passive” into something active. The same goes for lifting the knee actively. If the thigh comes through with enough speed, which will be a result of the stretch reflex and the inertial force of the thigh on the lower leg (because if the inertial force is great, then the lower leg will fold up towards the butt and increase the angular velocity of the whole leg coming through…). Put another way, the greater the force of hip extension/moving the thigh backward by application of force to the ground, the greater the knee lift will be in the front. Why? Because the thigh would shoot through “quicker” because of the greater stretch reflex. Thus…why when you sprint, you generally have a higher knee lift then when jogging…You’re not extending the hip/thigh as quickly or as much.

Arm Swing

While there are a lot of other examples, one I’d briefly like to discuss is arm swing. The reason I’m mentioning this is it’s relatively easy to feel the stretch reflex at play. In this case, swinging your arms backward will create a stretch reflex that aids in moving the arms through the forward swing phase.

It’s pretty easy to feel. Go stand in front of a mirror and just start stroking your arms. Start with an easy tempo and then increase the tempo and range of motion. If you are swinging your arms back appropriately, you can easily feel the effects of the stretch reflex. Just mess around with it for a while and you should be able to get it. This whole arm swing mechanism is why you primarily focus on the backswing and stroking your arms, not bringing them forward.

One last thing I’d like to mention briefly about arm swing, is that the arms and legs work in concert. Arm swing is a great way to control tempo and stride rate/length. For example, why do people open up the arms and stroke them when kicking it in? To increase stride length because the arms are going through a bigger range of motion, the legs will too.

Just a quick tip, the arms and legs counteract the angular momentum of each other. Upper body rotation/arm swing problems can be used to identify lower leg problems and vice versa. Most of the time what I’ve found is if you fix the arm swing, the legs will compensate and “fix” too. It’s why you’ve got to take a whole body approach and not isolate.

So what the heck do I worry about?!

You’ve got to make sure everything is in the right position to work correctly. The biggest lessons are learning what NOT to do. That being said, this isn’t a post about how to change form. The quick and dirty cheat sheet guide is to pay attention to the following:

Body position –slight lean from the ground, everything in alignment, moving forward, not wasting motion. Foot strike (not only where on the foot, but more importantly where in relation to COM) Hip extension once you hit the ground (Downwards and a little back. The key is starting hip extension once the foot hits the ground and ALLOWING it to happen and not trying to rush it or cut it off short…or as I like to invoke my inner info commercial…just set it and forget it…) Arm stroke- arms are your gas pedal. Use them to control the tempo. Relaxation

Static vs. Dynamic

Passive and Active are very much related to static and dynamic. If you’ve suffered through this post long enough, you’ll realize that the body has to work differently in a dynamic state than a static one. The stretch reflex, SSC, and inertial forces, for example, all rely on relatively quick movements. They don’t happen if we move really slow through the same range of motion. That means that the way we work dynamically is completely different than how we might work statically.

This has a couple major implications. First, you can’t really use static tests or static range of motion to tell you much about a dynamic movement. My favorite example is that Carl Lewis couldn’t touch his toes, yet watch him long jump and his dynamic range of motion was incredible. If you don’t believe that story, I’ll demonstrate on myself…

Ask anyone who has run with me and they’ll tell you my static flexibility is horrible. I’m completely useless. Even when I wear high socks to run in, I can’t come close to being able to bend down and touch them. The pictures below illustrate this. In the first one, I’m actively raising my heel as close as I can get it to my butt. In the second one, I’m pulling my heel to the butt as far as I can without feeling like my quads about to be ripped. It’s pretty apparent that if you looked at these pictures, you’d realize my static range of motion sucks…it’s horrible…

But, what happens when I sprint? Well, my heel somehow is able to make it right under my butt with no problem. It doesn’t feel like my quads going to rip or like there’s anything abnormal about the range of motion it’s going through. It is a perfect example of Static VS. Dynamic!

The point in mentioning this is to not fall into the trap of doing stuff like static flexibility or range of motion tests and then using those to explain someone’s movement in a dynamic situation. For example, if a runner doesn’t have a high back kick and a trainer/coach notices they have horrible static hamstring flexibility, the conclusion is often that the kid needs to stretch more so he can get that range of motion…Well that would be wrong. Runner’s muscles are often “tight” statically because a tight musculo-tendon unit is “stiffer” which means it can work as a spring better, storing more elastic energy than a completely loose muscle. Our body isn’t dumb; it tries to become efficient at what we do. That’s the reason why research studies show that runner’s with worse sit and reach scores have better Running economy. Does that mean no static or dynamic stretching? No. Because remember that most of our mileage is run at relatively slow paces, so we primarily adapt to that. That’s why you need some dynamic flexibility work, or more importantly some sprinting or faster running where the range of motion is much higher throughout the year. To finish the static vs. dynamic section, I’ll quote a dissertation by James Smoliga (2007) where he said, and backed up with research:

“Functional MRI imaging has revealed coordination between the upper and lower body to be a complex task controlled by multiple areas of a motor network, distributed across cortical and subcortical regions of the brain61. Coordination of the arms and legs is task-specific, with a reflex pathway active during locomotion 73, 112, but not during tasks performed while standing or seated73 “ So What?

The whole point is to be informed. It’s easy to look at a picture or a video and realize what you see. But what matters is the why and how what you see is happening. Not being able to distinguish the above things is what separates the so-called “guru’s” and the people who actually know what they are doing. Sorry if it sounds harsh, but with the rise of the barefoot running stuff and the interest in running form, there are a lot of people trying to make $ of runners who don’t know any better… The danger with using EMG: Lastly, a section I’ve added on because Pete Larson requested it…EMG is a way we measure electrical activity in the muscle. EMG simply tells you when there’s an electrical signal going to the muscle. So it can basically be used to tell if the muscle is “on” or “off”. It’s a tremendous tool. What it doesn’t tell you is important to understand. It doesn’t tell you where the nervous impulse originated, whether it was through higher motor centers, from a Central Pattern Generator in the spine, or as part of a reflexive adjustment based on feedback. More importantly, it doesn’t tell you what the muscle is doing. Just because it’s “active” doesn’t mean it is being used in a primary contraction/force production way. For instance, if we look at the concept of muscle tuning in the lower leg, an EMG might show that there is some pre-activity going on in the muscles of the lower leg for example before we even strike the ground. That doesn’t mean the lower leg muscles are necessarily being actively contracted by the individual to dorsiflex the foot or try and get the “force generation” going early. Instead, what is going on is that the whole lower leg complex is “muscle tuning” meaning it’s adjusting the characteristics of the musculature such as stiffness to prepare for the force absorption that will occur when the foot collides with the ground. Another great example is in the hamstring muscle group during the swing phase as the leg swings through, unfolds and is getting ready to touch the ground. As the leg swings through, you often get an EMG activity signal. This is sometimes interpreted as the hamstring being active so that the lower leg unfurls and then there is a large active pawback where the runner tries to contract the hamstrings a ton to get the foot moving in the same direction as the ground. What’s really happening is that as the leg comes through and the lower leg unfurls, the hamstring is simply active to slow down the lower leg unfurling. Because the thigh and lower leg swing through with a lot of momentum, the hamstrings work to counteract the lower legs unfurling momentum so that it doesn’t just keep going until the leg is straight. If the hamstring didn’t contract to provide just enough “braking” while the lower leg unfurls, we’d have a lot of runners landing with their whole leg in a straight line far out in front of them. These are only two examples, but many more can be given. The “core” is an excellent example that I’ll try and delve into some other time. Additionally, it is hard to separate out the stretch reflex mediated signal from a higher level motor signal. The stretch reflex will elicit an EMG response, so unless the study is designed to, it’s hard to figure out how much the stretch reflex (or even if one contributes at all) contributes to the EMG signal. The point is that EMG only tells us when the muscle is on/off, not what it’s role is or where the signal is coming from.