Introduction to Running Biomechanics

bi·o·me·chan·ics

/ˌbīōməˈkaniks/

Noun

The study of the mechanical laws relating to the movement or structure of living organisms.

If the above has turned you off slightly, I totally understand. It’s hard to go for a run these days without worrying about where our foot is landing, what shoe we’re wearing, or optimal stride frequency.

Surely running can’t be so complicated! The good news is, it doesn’t have to be!

The first thing you can do is discount anybody out there who tells you that their way is the only way. If that were the case, all elite, world-class runners would have the same running style, and quite simply they don’t.

Running, like any sport, is a skill for which improvement will depend on suitable conditioning and active development, but it’s about building on your individual running style, as opposed to basing your training regime on what happens to work well for somebody else.

Having a basic understanding of the biomechanics of running can help you appreciate your own running form and see where you may be able to make improvements. It can also help you make more sense of what you read and hear with regards to running styles, training programs, conditioning exercises, footwear, etc.

Although running most definitely depends on whole body interaction, dividing the running stride up into individual components or “phases” can help us understand how slight changes can help improve performance and reduce susceptibility to injury.

Getting Started: The Gait Cycle

Our introduction to running biomechanics can begin by looking at what we call The Gait Cycle. This cycle starts when one foot makes contact with the ground, and ends when that same foot makes contact with the ground again.

It can be divided up into two “phases” – the stance phase (during which the foot is in contact with the ground) and the swing phase (during which the foot is not in contact with the ground).

The stance phase is typically considered as the more important of the two as it is when the foot and leg bear the body weight. The swing phase is (or rather should be) passive, i.e. not consciously controlled.

Trying to actively help the leg move through the swing phase is an example of where runners can waste energy, e.g. by consciously trying to lift the heel higher towards the backside, or trying to lift the front knee higher. We’ll look at that in more detail in weeks to come. For now, let’s look at the components that make up the stance phase.

The Stance Phase

This can be divided into four stages: initial contact, braking (absorption), midstance, and propulsion.

1. Initial contact

Let’s imagine you are at that moment in your stride when both feet are off the floor (sometimes referred to as float phase). Your left leg is out in front of you and about to touch the ground. This moment (whether you land on heel, midfoot, or forefoot) is called initial contact and marks the beginning of the stance phase. Your right foot behind you is off the floor and in swing phase.

2. Braking (absorption)

As soon as your left foot makes contact with the ground in front of you, your body is in effect performing a controlled landing, managed via deceleration and braking. Your left knee and ankle flex (the opposite of straighten) and the left foot rolls in (pronates) to absorb impact forces. During this process of absorption, the tendons and connective tissue within the muscles store elastic energy for use later in the propulsion phase.

3. Midstance

The braking phase above continues until the left leg is directly under the hips taking maximum load (maximum risk of injury) as the body weight passes over it. The left ankle and knee are at maximum flexion angle. This moment is called midstance (you may also hear it referred to as single support phase).

4. Propulsion

Now that your left leg has made a controlled landing and absorbed as much energy as it’s going to get, it starts to propel you forwards. This is achieved by your left ankle, knee and hip all extending (straightening) to push the body up and forwards, using the elastic energy stored during the braking phase above. The more elastic energy available at this stage, the less your body has to use the muscles.

The propulsion phase ends when the toe of your left foot (now behind you) leaves the ground, commonly referred to as “toe off” (TO). At this point, both of your feet are off the ground so you are once again in float phase.

Research shows that at least 50% of the elastic energy comes from the Achilles and tendons in the foot.

The Swing Phase

At the moment of toe off, your left leg has travelled as far back as its going to and the heel starts to lift towards your backside. As I mentioned earlier, this is a passive movement (as opposed to a conscious effort), with the height that the heel reaches depending on the degree of hip extension achieved and the speed you are running at.

Steve Magness, Head Cross Country Coach at University of Houston, compares this stretch reflex mechanism to the stretching back of a sling shot and then letting go. Extension of the hip (as your back leg moves behind you prior to toe off) is equivalent to pulling back on the sling shot.

Letting go results in the leg firing forwards rapidly, leading with the knee. Any conscious attempt to move the leg through the swing phase (Steve refers to it as the “recovery phase”) results in wasted energy and a less powerful firing of the slingshot.

Once the knee has passed under the hips, the lower leg unfolds in preparation once again for initial contact, marking the end of the swing phase.

Upper body and arm mechanics

The interaction between the upper and lower body plays a vital role in running, the upper body and arm action providing balance and promoting efficient movement. This balance is achieved by the arms and upper body effectively working in direct opposition to the legs. Bringing the left arm forward opposes the forward drive of the right leg, and vice versa.

During the braking (absorption) stage described above (initial contact to midstance), the arms and upper body produce a propulsive force.

During the propulsion stage (midstance to toe off), the arms and upper body produce a braking force.

By working as opposites, forward momentum is maintained. The arms and upper body also counterbalance rotation in the midsection. For example, as the right knee is fired through in front of the body (right swing phase) an anticlockwise momentum is created. To counterbalance this, the left arm and shoulder move forwards to create a clockwise momentum to reduce rotational forces.

To help the above occur as efficiently as possible, arm swing should be initiated at and through the shoulders. Driving the elbows down as well as back can help avoid elevation of the shoulders, which in itself causes tightness and limits range of motion.

Just as bringing the knee through in swing phase needs to be a passive movement, so does the forward movement of the arm. Driving your arms up and forwards wastes energy and reduces the efficiency of the stretch reflex mechanism in the shoulders. Your hands crossing the midline of the body is a sign that you may be driving the arms forwards instead of backwards, or that you have tightness in the chest.

Correcting arm crossing can increase efficiency, as can ensuring that the elbow angle only changes slightly (as a result of elastic response as opposed to active movement)

On a final note, bringing the arm too far back (or forwards) can lead to over striding which, as will be discussed in future articles, can cause excessive braking and lead to injury.

Improving your mechanics

Next week, we will look at how modifications to your running form can help increase biomechanical efficiency and current thought on how we can achieve these modifications.

There are many suggested methods out there – isolated exercise, functional exercise, drills, cues, etc. so we will take time to consider them in more detail.

I will leave you with this thought though: It is generally agreed that changes to habit, and therefore running form, cannot happen through consciously forced technique changes. Instead, they need to be learned over time through an unconscious evolution that can be broken down into the following four-stage process:

1. Unconscious Incompetence

At this beginning stage, you are unaware of any need to improve and so cover your running distance without suspecting anything needs changing.

2. Conscious Incompetence

Armed with your new knowledge of biomechanics, you now run conscious of where you could be improving your efficiency. By performing suitable strength & conditioning and/or working with a coach, you can begin to make modifications.

3. Conscious Competence

Through adequate conditioning & correction, you now run with awareness of what you are doing better. There are times when you still need to think about your running form so it is not yet coming completely naturally.

4. Unconscious Competence

Congratulations! You have managed to change your form and do not have to think about it whilst running.

If you’re interested in learning more about how to improve your own running form and develop the most efficient stride for YOUR biomechanics, signup for our 6-week online form course. The online course will help you run with proper form by teaching you the science of running biomechanics and provide you with a simple-to-follow, progressive set of exercises, drills and mental cues to help you make lasting changes to your form.

Are you a runner who has managed to modify your running form and seen an improvement in running efficiency? Have you have also seen a reduction in injury? Or, maybe you tried and ran into new problems! Whatever your experience, we are as always keen to hear from you.

Happy running!

Matt PhilipsMatt Phillips is a Run Conditioning Coach, Video Gait Analyst & Sports Massage Therapist with over 20 years experience working within the Health & Fitness Industry. Follow Matt on Twitter

 

References

1. Sasaki, K & Neptune, R (2005) Muscle mechanical work and elastic energy utilization during walking and running near the preferred gait transition speed http://www.me.utexas.edu/~neptune/Papers/gait&posture23(3).pdf
2. Magness, S. Running with proper biomechanics http://www.scienceofrunning.com/2010/08/how-to-run-running-with-proper.html

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18 Responses on “Introduction to Running Biomechanics

  1. SO my arms produce a propulsive force? Ive tried swinging them but I don’t seem to be going anywhere what am I doing wrong?
    Nice quote from Romanovs posemethod book though, shame you didn’t acknowledge.

    • Hi Dimble. Thanks for the question.
      Evidence suggests that the arms generate less than 1% of overall acceleration in running but they do effectively counterbalance the momentum of the legs (Hamner.R et al.,2010). The propulsive force of the arms that I mention in the article is not a conscious effort. It is part of the mechanism the body uses to achieve balance and maintain forward momentum, i.e. when the left leg is forward the right arm is forward, when the forward knee is at its maximum height, the opposite arm is at its maximum height, when the back leg is at its maximum extension the opposite arm has moved to its maximum back position, etc. In theory, this should all come naturally but in reality muscular imbalances (and unconscious habit) can often restrict optimal movement in one/both of the shoulders and arms, which in turn can affect leg movement and thus overall running efficiency. So, although consciously trying to swing your arms is not the answer, checking you have balanced, efficient movement in the arms can be a good way of improving running performance. I hope this helps you.
      (With regards to the “quote from Romanovs posemethod book”, could you let me know which sentence you are referring to so I can add acknowledgement where due? Many thanks!)

    • Very nice article. It is definitely hard to cover all of the bio-mechanics at work in running but this is helpful. If you do not sense your arms contributing effectively it could be because of weakness in the “core”. The force may not be transferred efficiently through to the shoulders and is being dampened in the torso. One of my favorite expressions “you can’t push a rope”. Spine may be absorbing these forces which could lead to pain. One technique you can try to facilitate/investigate arm force in your run is to sit on the floor with your legs straight out in front of you. Gradually begin to swing your arms as if running. You should be able to get yourself bouncing off each side of your ischium(butt)-without leaning. If not, there is probably a “leak” in the stabilization.
      As far as shoulder(scapula) elevation/extension, I think alot of this comes from weakness in gluteus maximus and runners are recruiting the shoulder to attempt to support or even extend the hip (not a good strategy). Strengthen the hip extensors, stabilize the scapula, and allow the counter-rotation forces to translate out into humeral motion. For more info, see the Joint-by-joint approach.

  2. I know running is a science, but this is crazy, so much to think of. I have rolling feet, which I know impairs my run. I have some inner soles made especially for me, but wonder if I actually need them?

    • Hey Sam. Don’t worry, you don’t have to know any of this to run! :-)
      Some folk do like to peel off a few layers to see what’s underneath but it°s not mandatory whatsoever. The two things I’d like people to take away from this is: 1. Running efficiency can be improved if you put the right work in. 2. Risk of injury can be reduced if you put the right work in. The ins and outs can help you understand why, how and which exercises are suitable for you but you°ll get the benefits by just doing them too!
      As far as the question of inner soles goes, that could be a whole new article but I will leave you with a thought… if they don’t feel comfortable, try without. As long as you test footwear slowly and gradually, your body will tell you soon enough if something is not working for you. Comfort is becoming more and more the best method to decide on footwear, as long as you take your time and listen to your body. And remember, whenever you try something new or return from injury, never jump straight back in to where you left off. Always regress a little to give your body a chance to talk to you!
      Hope this provides food for thought. Let us know how you get on!

  3. Hi Matt,

    Great article! Loads of good info here that should really help runners make sense of the basics in the puzzle that is human running biomechanics :)

    I’m always a little frustrated by Steve Magness’ comments about swing phase:

    “Any conscious attempt to move the leg through the swing phase results in wasted energy and a less powerful firing of the slingshot.”

    I feel that the “conscious attempt” needs a little qualification…

    I agree that much of hip flexion from early swing phase to the recovery phase of swing must come from the stretch reflex “slingshot effect”, having loaded the hip flexors into extension at terminal stance.

    While I also agree that any conscious effort to flex the hip by “driving the knee forwards” (using Rec.Fem. etc… to drag the leg through swing phase) is counter productive and adversely affects efficiency of the swing leg. It’s important also to note that in many recreational runners, improving hamstring activation in swing phase can assist in reducing torque at the hip, through changing the centre of mass of the swing leg as the knee flexes.

    I’ve found that getting many recreational runners to combine an increased cadence with a *slightly* increased hamstring based heel-lift in swing phase can reduce the tendency to run in such a way that overly depends on the quads and hip flexors. Rec.Fem. in particular.

    Coupling the conscious action of the hamstrings with the stretch reflex action of the hip flexors / quads seems to produce a far more balanced environment around this hips and pelvis. I’ve had many runners almost immediately resolve lower back issues for example through changing the action of the swing leg.

    I’m not talking about Pose specifically. I’m not a Pose coach, and see flaws in some Pose elements. But this particular element of swing phase is similar to the heel lift action described in Dr. Romanov’s work – lifting the foot straight upwards with the hamstrings to create combined knee and hip flexion – offloading the hip flexors.

    Perhaps Steve’s comments are born from the fact that the high-level XC athletes he works with all naturally display a reasonable hamstring based heel lift – as with many competitive runners… but what about the 10min mile “shufflers” we both work with on a daily basis, dragging their legs through from stride to stride, long levered and overly reliant on the anterior chain?

    Enough of my ramblings :)

    • Hey James. Firstly, thanks for taking the time to comment. Honoured to have feedback from a coach of your knowledge and experience. Hopefully we can get Steve in here too to respond to your points directly!
      Like yourself, I am a big fan of using gradual cadence (stride rate) increases to improve running efficiency (next week’s article focuses on just that!) and I find one of the many benefits from it is promotion of a natural increase in heel lift. As I see it, the higher stride rate increases force to the ground closer to COM which in turn increases force of hip extension, the front knee lifts higher, the back foot lifts higher, creating a greater stretch reflex which takes us round the cycle to start again with increased force to the ground. I therefore typically tend to shy away from encouraging any active recruitment of the hamstrings to consciously increase heel lift as I have always believed it can interrupt and weaken the aforementioned passive process. That said, without sufficient strength and mobility in the hips, this natural process is hindered from the start, so I understand your point that a “slightly increased hamstring based heel lift” can be used to offload the hip flexors. Is it something you use solely with recreational runners who have insufficient hip strength and mobility to depend on the passive process? What happens if/when they build up sufficient conditioning to no longer need it? Presumably the idea is that what starts off as a conscious lift eventually becomes unconscious and part of their running style, so do they have to “unlearn” it?
      Thanks again James. I look forward to your reply!

      • Completely agree that improving cadence is normally a great place to start. In addition, I tend to begin with hip mobility, as the vast majority of runners I meet are deficient in hip extension and sometimes relative internal rotation.

        In runners who display a lack of ability (through poor mobility) to get real benefit from the stretch reflex at the hip, I do find it useful to add the cue of slightly lifting the heel – ‘picking the foot up’ though swing phase. This gets the hamstrings fired up a little, and assists in what would have otherwise been a laboured, anterior chain dominant swinging motion, with little help from the passive stretch reflex ‘slingshot’.

        You’re probably right though, as hip extension improves in the runner, this may become less important as the loaded hip extension is ‘winding-up the rubber band more’ in the slingshot :)

        It may well be that the conscious cue of adding a little lift up of the foot, using the hamstrings adds a little more in terms of effort while the body adapts – but what it does in my opinion is improve muscle balance and torque around the hips / pelvis as the leg swings though.

        Many of the injured runners we both see, have injuries which stem from muscular imbalances around the hips and pelvis. It’s the common ‘lazy running gait’ of pulling the ‘long lever’ swing leg through using the quads / hip flexors primarily, combined with poor hip extension (ineffective stretch reflex) that places excessive load on the hip flexors / quads / ITB (as TFL may be recruited to assist hip flexion).

        Talking as a coach/rehab therapist, rather than a coach/exercise physiologist, I’m happy to see a runner use a *little* more effort to improve their gait if it results in improving muscular balance and overcoming injury. Performance benefit then comes from a well execute training block without the interruption of injury!

        A great example of this is the classic desk-job bound 4hr marathon runner hit with ITB Syndrome once a certain volume is hit in training. Poor hip extension means that they don’t benefit enough from the stretch reflex ‘slingshot’ to assist hip flexion. To overcome this they recruit any other muscles that can act to flex the hip. Maybe because of it’s extended lever arm via the ITB, TFL is an obvious choice. TFL increases in tone, leading to increased tension in the ITB. Getting the hamstrings to assist hip flexion, helps to break this dysfunctional pattern, while we also work on hip mobility, stability, cadence, posture etc… An overly simplified explanation!

        • Great points and a good reminder of the importance of working with the athlete in front of us as opposed to following a recipe from a book.
          I hope Steve pops in to leave a follow up.
          By the way James, you have a double who was at the recent Brighton Marathon 2013 Expo. His name is not James, as he made perfectly clear when I tapped him on the shoulder and said “Hey James, how’s it going?”

    • Hey Adrian, sorry about the delay in getting back to you. Great to hear you enjoyed the article, thanks for the comment!
      There are many great articles shared on Runners Connect on a weekly basis, as well as a podcast I recommend you check out. I post links to the articles I write here.
      Thanks again, Matt.

  4. Good article! In several race pictures over the past couple years, I have noticed that my airborne ‘back foot’ points ‘out’… It has happened to frequently to think it is just the picture angle. Somehow it gets back to square at footstrike, but I have to think I am losing efficiency to go along with my crazy looking pictures. I have googled and cannot find anything. Thoughts on why I do it and how to correct it?

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