Learn About Running Form: Frontside vs Backside Mechanics
6 min read
We work with a lot of runners and the first question they often ask is how much of their running form we seek to change. Although the answer is contextually dependent, the principle is the same. Our goal with any patient is to move them away from what they are demonstrating too much of towards what they are currently not demonstrating enough of. In doing so, the goal of our rehab and performance is to simply provide you with more options to complete a higher level task, essentially giving you some of what you are currently lacking.
Why Is This Important?
In the context of runners, it is most common for the runners we have worked with to demonstrate more backside mechanics compared to frontside mechanics. This blog will help you understand exactly what that means.
The Running Cycle
The running cycle can be split up into ground time and air time. Ground time is associated with the time in which your foot is on the ground producing force while air time is the time in which neither foot is in contact with the ground. The ratio of ground time to air time is often classified as one's drive index, with 0.75 often representing “neutral”, such that more time is spent in the air than on the ground.
Frontside vs Backside Mechanics
Simply put, frontside mechanics is everything that happens in front of the body while backside mechanics is everything that happens behind the body, if the body were to be cut into front and back halves from a side view. Runners who bias frontside mechanics will demonstrate greater hip and knee flexion and longer air times, thus allowing their knee to drive up and forward with each stride. In comparison, runners who bias backside mechanics will demonstrate greater hip extension and longer ground contact times, thus producing a longer push off phase.
Photo on left depicts a leg that trails behind the runner, which is classified as being more backside.
Photo on the right depicts a leg that comes up and forward, in front of the runner, which is classified as being more frontside.
Which is optimal?
To reiterate, no one extreme is desired, however, certain mechanics do demonstrate pros and cons. In general, most runners, especially novices, demonstrate greater backside mechanics and poor frontside mechanics. Is this a bad thing? Let’s weigh the pros and cons.
Frontside mechanics allows the leg to better prepare for ground contact with each step. By being more frontside, the leg has more space and time for muscles, such as the hamstrings, to contract prior to initial contact. This pre-activation of muscles before initial contact allows for stiffer landings and more vertical force production, both of which means the runner has to spend less time on the ground.
With that said, backside mechanics allows the leg to produce greater force once on the ground thereby leading to a stronger push off. As you can see, the preferred mechanics are dependent on what the runner needs relative to what they currently have.
Most often, runners lack the ability to access greater hip and knee flexion angles, the functional stiffness needed for reduced ground contact times, and the ability to “pre-activate” prior to initial contact for vertical force production, all of which cause them to fall into a very backside pattern. Again, backside mechanics isn’t inherently bad, but as it becomes overly relied upon is when we start to see things break down.
Where we see backside mechanics fall short
Falling into a very backside pattern causes your trailing leg to lag behind with every step. This lag coupled with mobility limitations that are often accompanied at the pelvis causes your pelvis to dump forward into an anterior tilt, thus causing your low back to arch excessively. This position of low back extension and anterior pelvic tilt limits your ability to drive your swing leg forward with each step, as your hip cannot access as much hip flexion with a pelvis that is tilted forward. Moreover, this forward orientation of your pelvis creates tension through your hamstrings given their attachment to the back of your pelvis, thereby limiting your legs ability to achieve frontside lift.
As a result of your pelvis being pushed forward, your low back being arched excessively, and your hamstrings being in a poor position to create that pre-activation prior to initial contact, your lower leg is excessively kicked out in front of you (overstriding) producing a horizontal (braking) force rather than a vertical force at initial contact. That is one of the most common mechanisms of a hamstring strain. As a result of this horizontal (braking) force, functional stiffness in the leg is lacking during ground contact, thereby limiting your ability to quickly recoil into the next stride.
Essentially, you need proper frontside lift to create the vertical force into the ground that is necessary to create a more ideal drive index (time on ground versus flight time). By creating more horizontal force through backside mechanics, you are not only spending too long on the ground but also imparting a braking force with each step, thereby slowing you down and minimizing the force you are putting into the ground.
Correlations to Higher Performance
For the previously stated reasons, we most often seek to achieve mechanics that are more frontside, relative to peoples typical baseline. By increasing the forward knee drive, your leg is better prepared to produce force into the ground, thereby minimizing the need for ground contact all while maintaining a more ideal position of your spine, pelvis, and hamstrings. As with all things in movement, backside vs frontside mechanics exists on a continuum, therefore our efforts towards frontside mechanics depends on how backside the runner is at baseline, and vice versa. If you are having trouble visualizing the two patterns, think of exaggerated backside mechanics being butt kickers and exaggerated front side mechanics being high knees, with progress towards the latter most often being the goal of intervention.
Lots of forward knee drive amongst all these sprinters
Cuing Frontside Mechanics
Run as if you are ascending a set of stairs. In doing so, the runner will have to create greater knee drive up and forward to clear each imaginary stair, thus producing greater frontside lift.
Attack the ground straight down (not back) as hard as you can with each step. In order to truly strike the ground hard, you have to drive your knee as high as possible to allow for more time to accelerate your foot into the ground, thus producing greater frontside lift.
Stay vertical. By remaining vertical you prevent your low back from over extending (arching) thereby preventing your pelvis from dumping forward. Positions opposite of this excessive anterior pelvic tilt and lumbar extension will maintain adequate hamstring positioning to allow for subsequent front side lift and pre-activation before ground contact.
Arms forward and upward are also effective in maintaining the aforementioned vertical posture for frontside lift.
Here is a photo of one our patients doing a good job of hitting these cues.
Conclusion
Although the pros and cons make frontside vs backside mechanics contextually dependent, in general, we seek to move our runners away from backside mechanics by giving them the ability to move into more frontside mechanics. Once your mobility limitations are corrected such that you can move into a more neutral, frontside pattern, we seek to develop strength and elasticity through this pattern to eventually build capacity. If you are interested in hearing about how we can bridge the gap between where you currently are and where you are trying to go, schedule a free discovery call.
References
Josse, C. (2020, April 15). Sprinting in Team Sport: The Butt-Kicking Epidemic. SimpliFaster. https://simplifaster.com/articles/sprinting-in-team-sport-the-butt-kicking-epidemic/
McNally, O. (2021, February 28). A Bias Toward Speed? Breaking Down the Sprinting Cycle. SimpliFaster. https://simplifaster.com/articles/breaking-down-sprint-cycle-video/
