Ask the Expert: What is Running Dynamics

What does the perfect running form look like? The short answer is: it depends. All runners are not built the same. You will not look like or run like every training partner you have, or every individual you line up on the start line against, and you shouldn’t! We are all built differently. Some of us are tall, some are short, some have long legs, some have long torsos. While there will always be the keyboard warriors who will comment on what an individual’s form “should be,” the truth is, the norm for form is different for each individual. Though there is no cookie-cutter approach when it comes to running form, there are good principles to understand and aim for to achieve good individual running form.  Is there an optimal cadence that we should try to strive for, or is our natural cadence best? What about vertical oscillation, and how does this pertain to me? Do I need to decrease my ground contact time and how can I? With advancements made in technology at our disposal, it is easy to get lost in the hype of measuring running dynamics. What do these even mean, and how do they apply to my own training? 

What is Running Cadence?

The term cadence originates from the Greek term “to fall”.  While mostly used when talking about music, it is very appropriate to think of the origins of this term for running.  In running, cadence means steps per minute, or “how many times does your foot land (fall) per minute?” Most running watches will measure your speed/pace in units of “miles per hour,” or in “minutes per mile.” (Also can be programmed for metric units as well!)  In regard to running cadence, we only ever talk about Steps Per Minute. 

In cycling, cadence is commonly referred to as “Revolutions per minute,” meaning: how many times over a 60 second period does your crank rotate 360 degrees.  If you look at just your left foot for cycling cadence, you must go from the 12 o’clock position with your left foot all the way around the crank until your left foot is back at the 12 o’clock position.

With running, one step is one foot striking the ground.  You can think of this in cycling terms as your left leg going from the 12 o’clock position down to the 6 o’clock position counting as “1”,.  This is the main reason why running cadence and cycling cadence are so different.  A “good” cycling cadence is 90 rpm, while a “good” running cadence is 180 rpm. For those good with their quick mental math, you will have noted 90 x 2 = 180 rpm.  Given that cycling cadence is measured at half the frequency of running cadence, you should notice there is no coincidence that 90 rpm and 180spm are both considered by many as the “Optimal” cadence.

What is the importance/impact of cadence?  

Are you a runner who naturally has a high turnover and shorter stride length, or are you a runner who takes longer loping strides with a slower turnover? Is there a preferred cadence you should be striving for? While it is possible to maintain a given running speed with large ranges in cadence, this can often lead to running cadences that are highly inefficient.  

Let’s look at an example of two scenarios: Imagine running an 8-minute mile completed by taking incredibly short and quick steps.  You are essentially “shuffling” across the ground.  Conversely, you can significantly decrease your cadence to maintain that speed, but you are now “leaping” from step to step.  I’m sure you can imagine getting incredibly winded trying to maintain that pace while shuffling and can imagine your legs simply giving out after a couple minutes of massive leaps. (That would be a lot of single-leg squat jumps!)

While everyone’s optimal cadence is different (just like everyone’s heart rate is different) there is still a narrow range that everyone’s optimal cadence exists.  No one is taking 2 steps per minute and hitting an 8-minute mile, just like no one is taking 360 steps per minute and hitting an 8-minute mile. Then what does good running form look like? Again, this is different for everyone and the main goal of cadence and form is to be as economical as possible at a given speed, running as stress-free as possible, and being as symmetric as possible.  

Keeping these two examples in mind (leaping vs shuffling) it’s easier to understand Vertical Oscillation and Ground Contact Time.

What is Vertical Oscillation?

This value represents how much your center of mass moves up and down for each step. From a physics perspective, it takes energy to move an object up and down, this is: against gravity.  More vertical movement means more energy is required.  

Let’s go back to the above example of the shuffler vs the leaper. The “leaper” is having to jump fairly high in order to travel far enough vertically to maintain that 8 minute pace.  Whereas the “shuffler” isn’t even moving their body off the ground, they are just transitioning from one foot to the other.

The “leaper” will have a far greater vertical oscillation (VO). They have to apply more force vertically (longer air time) to ensure they travel the distance required to maintain that pace. This increased vertical height also means your landing foot needs to absorb more energy as it comes to a complete stop. The extra impact can be absorbed by the spring-like achilles, the energy can be “stored”, and then “released” using their achilles as a spring, also known as elastic energy.   Adding this spring force to each step means less force is required by the muscles.  The more you recoil a spring, the more energy it can store and “give” back.

When we look at our “leaper” and “shuffler” you can see how the leaper is taking advantage of that spring action, thanks to that large VO, while the shuffler is getting almost no energy return out of their achilles. Logic would say that being a “leaper” sounds awesome right? Well not exactly. Your body can store more energy in your achilles with a greater landing impact, but that load doesn’t just go to your achilles, it is transferred through your entire body.  Adding that much extra load and strain to your whole body over an hour of running can significantly increase your chances of getting injured. Injury risk increases when you are an individual with stiff ankles, poor mobility, and flexibility, or improper biomechanics. If you continue loading large forces onto your body this leads to tissue and bone damage. If there is one thing everyone can agree on, being injured does not make you faster.

What is Ground Contact Time?

Ground contact time (GCT) represents how long your foot remains on the ground between impact and lift off. Let’s circle back to our friends: the leaper and shuffler. Our leaper has a much longer ground contact time (as their achilles, lower leg, and torso absorb the energy of their last leap) whereas the shuffler has a much much shorter ground contact time. This is the piece that really brings Cadence and Vertical Oscillation together. At these extremes, Cadence has a significant impact on VO, and therefore a significant impact on GCT.

Increased GCT is correlated with an increased risk of injury. This is not to say that every runner who exhibits a higher GCT than others will inevitably end up with injuries. This can be useful though to those who tend to the injury-prone side. If you find yourself with increased lower leg injuries than most, potentially a deeper dive into your biomechanics can help address some issues that can be causing a disruption in your lower limb health. Ground contact time is synonymous with braking force. Peak braking force is the amount of energy that is directed into your leg from front to back. Think of sprinting at maximal speed and then coming to an immediate stop. The force you feel when you slam on the brakes is your peak brake force. Our bodies were not designed to handle high shearing forces. Our muscles, bones, and tissues are suited to handle forces transferred up and down. Reducing your braking force will help and aid in injury prevention. Going back to the leaper, this runner’s GCT (braking force) is much higher due to their very large stride length.

Changing your running form was never going to be easy, and will take time and diligence with acute attention to every detail. When details matter, making real-time changes becomes crucially important. The ELEMNT RIVAL is able to broadcast your heart rate, running pace, and running cadence to other devices such as bike computers, treadmills, and 3rd party apps.

With all of this data at your disposal, it is important to keep in mind that everyone has a unique cadence and vertical oscillation. While 180 may be the magic number, do not become attached to it. Use it as a guideline for you to help improve running form and increase your running economy. Technology allows us to better understand our bodies so that we can get the best out of ourselves, and most importantly spend less time injured to enjoy the things we love most.

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