The simple theory is that reaching your foot too far forward – from your center of mass (COM) – while running creates an inefficient gait and a possibly injuring impact.
You may have heard of or even had shin splints or lower-extremity stress fractures before. They’re not pretty.
The Physics of A Runner’s Stride
We know that these running injuries have to do with some relation between an individual’s center of mass and their stride, but since everybody is different, and the way we carry our bodies differs, it has been difficult to nail down.
A study by Chris Napier, a physiotherapist, biomechanics researcher, and runner at the University of British Columbia, aims to define overstriding in five distinct ways:
- The angle of your shin at the moment your foot hits the ground.
- The distance between your heel and center of mass at that moment of contact.
- The distance between your center of pressure and center of mass at moment of contact.
- The angle between your center of pressure and center of mass, cutting through a vertical line.
- The percentage of your total step length that takes place in front of your center of mass.
Not the easiest calculations to generalize for every runner.
Rate Of Impact Plays A Role In Injuries
The touchdown point of your foot, or foot strike, is a topic familiar to even beginner runners, but it’s important for a healthy run. It also involves a key variable in overstriding: loading rate.
The loading rate, or how quick and hard your foot impacts the ground, is higher when you land heel first, cushioning or not. It seems the farther your foot is from your COM as a heel-striker, the harder the impact. Conversely, the farther from the COM as a forefoot-striker, the softer the impact.
Higher loading rate means higher stress and potential injuries including shin splints, knee joint degradation, hip problems, lower back pain, plantar fasciitis, and more.
Unpredictable Running Conditions Play A Role
So, without knowing exactly what causes overstriding, what choices do you really have?
Due to the forgiving nature of the belt, treadmills tend to be easier on your body. An important point to consider when trying to avoid, or come back from, a lower extremity stress fracture.
How about the differences between treadmill and road running?
Footwear or the lack thereof is another decision. Some studies show a decreased loading rate with barefoot running, but a good running shoe is an important thing to consider as well.
It’s safe to say there are a lot of variables to consider, which is why the solution for overstriding has been so elusive. Researchers like Napier are getting closer, but for now all you can do is be conscious of your stride and not push yourself too far.