If you think back to high school Physics lessons, you might remember being taught about forces being transferred, rather than simply disappearing.
In the context of running gait, we can think about this with reference to the way in which we exchange forces all around the body; trading-off stress and strain on one tissue against that applied elsewhere as we alter loading patterns through changes in technique.
From an injury rehab perspective, this exchanging of forces and loading patterns from one tissue to another is one of the main premises underpinning our use of running gait re-education as an rehabilitation intervention.
As long as you know your functional anatomy, and have a good understanding of running biomechanics; making targeted small but meaningful alterations to running form can reduce stress and strain on a given tissue. However this usually results in increased stress and strain elsewhere. Not a problem as long as you give the runner’s body time to develop the required adaptation to the demands of the new loading pattern.
Commonly when thinking about stress and strain, we usually consider the way in which the runner’s body loads at initial contact and through into early stance phase of running gait, with the runner weight-bearing on a single limb. Essentially assessing how well the body deals with ground reaction force.
Late Swing & Early Stance Phases of Gait
The following 2014 study however, looks at how habitual forefoot striking runners differ in terms of muscle activity during late swing phase (in preparation for weight-bearing) and early stance phase (as they begin to weight-bear), in comparison to habitual rearfoot (heel) striking runners.
I found this research particularly interesting in looking at both the differences in kinematics and muscle activity between habitual forefoot strikers and rearfoot strikers, not just from initial contact onwards into stance phase, but considering what happens preceding initial contact.
I frequently meet runners who have recently adopted a forefoot strike (non-habitual by definition) and display a noticeably plantar flexed ankle during late swing phase, just preceding initial contact. See the video below…
It almost looks like they’re “reaching for the ground” with the forefoot.
Interestingly, the more pronounced cases of this are usually the runners complaining of acute calf tightness and discomfort as they make this transition from their habitual heel striking running gait to a forefoot strike.
Cueing these particular runners to remain relatively / gently dorsiflexed (essentially neutral at the ankle in the sagittal plane), rather than plantarflexing usually does wonders in enabling them to to run with much less of a reaction from the calf complex.
The authors of the paper in question perhaps begins to explain the mechanism we’re seeing in action. In the discussion of the full text, the authors cite Winter (2005) in stating that:
“…muscle activity precedes force production”
Knowing that in habitual forefoot striking runners we expect to see an increased internal plantar flexion moment at the ankle joint during early stance phase, the authors expected to observe increased plantar flexor activity immediately preceding initial contact, which is exactly what they saw.
I like to think of this simply as “pre-engagement”.
What About Heel Striking Runners?
When comparing the joint kinematics and muscle activity of the rearfoot striking group to the forefoot strikers, the authors noted that heel strikers tend to display less knee flexion at initial contact, meaning that they contact the ground with a ‘straighter’ knee.
The rearfoot strikers also displayed greater dorsiflexion and tibialis anterior EMG activity than the forefoot strike group during late swing phase.
In addition, these habitual rearfoot strikers displayed more lateral hamstring activity during late swing phase than the forefoot strikers. My feeling is that this is most likely due to the increased eccentric effort needed from biceps femoris to decelerate the tibia, as the lower leg swings forward into the more knee extended position.
The video below gives a good example or a more extended knee at initial contact, with more ankle dorsiflexion.
Of course, in slow-motion we can simplistically ‘eyeball’ the gross differences in joint kinematics compared to the forefoot strike video, but not see the muscle activation!
Food for Thought
That is of course what this all is, food for thought!
No concrete answers to be found here, but a good workout for the brain in understanding what we see from each of our runners, and what they experience in their own n=1 study.
It’s worth noting that in this study discussed above, the authors accept the potential limitations that stem from their testing being performed with the subjects treadmill running. Each runner was allowed to run in self selected footwear.
In the full text, they conclude by stating that their data is insufficient to draw conclusions about injury mechanisms, but helps to define the differences between forefoot strike and rearfoot strike patterns.
Let’s also not forget that “Not all Heel Strikes are Created Equal”