Not all impact forces are harmful when running, but when they’re produced in greater than
normal amounts, your chances of injury can certainly increase.
In fact, impact severity when running can be strongly influenced by foot strike pattern
whereby heel strike running tends to be most consistently associated with producing more
all-around impact levels than forefoot strike running.
One such impact variable in heel strike running that is a big risk factor for injury is called
the ‘peak brake force’ which is produced at heel strike; peak brake force means there’s
a heavy burst in collisional impact at heel strike.
Why is this force produced in the first place at landing in heel strike running?
It’s produced because most often, the farther back you land towards the back of the heel,
usually encourages overreaching with the foot and leg which usually accompanies a fully
unbent knee.
This ends up creating a long over-stride angle where there’s a long distance separation
between the mass of the body and initial foot strike position.
It’s this elongated distance that causes the body to come to a crashing halt for a
longer period of time and results in a burst in collisional impact that also produces high
compressive loading as well.
To that point, Runners World featured a study, which is linked below the video in the description
box, of which the research re-confirmed that runners with the highest peak braking force
were almost 8 times as likely to get injured than runners with the lowest peak braking
force.
The researchers mentioned why a high peak braking force when running is so injurious
is because bone withstands forces better if the forces are occuring in the vertical direction,
but not when forces occur in the horizontal direction of which braking force in the horizontal
direction has a strong, damaging shearing effect on most of the joints and soft-tissue
structures in the lower leg of which these areas aren’t built to withstand the shear
force from increased braking.
The study however focused on heel strike and midfoot strike runners, and suggested that
one way to reduce the brake force in these footstrike types is by increasing step-rate
or cadence which is the number of steps you take per min, and the cadence range most proven
to do the most good for injury prevention and performance improvements was found to
be between 170 to 200 steps per minute and what makes a higher cadence so effective in
limiting high brake stress is that it improves the foots positioning at landing in that it
enables the foot to land closer to under the ankle, knee and hips (hips being the center
of mass).
In this condition, the peak brake force is less intensive and shorter in duration, but
it's still higher as compared with forefoot running because in forefoot running, landing
forefoot-first literally eliminates the high peak brake force at landing; it complete removes
the burst in collisional altogether that is seen when you land behind the arch, high up
on the heel, like in a heel strike, but when you land ahead of the arch, on the balls of
the foot, not high up on the toes, but a much flatter foot placement, results in a greater
smoothness in foot placement; there’s a much smoother motion of the foot with the
ground that produces less jarring and jolt forces, in addition to completely eliminating
the high brake force, because the farther you land away from your heel, closer to the
front of you foot, like a forefoot strike, there’s a smaller inclination of the foot
relative to the ground upon touchdown.
This means the forefoot doesn’t like up like it does in a heel strike landing, rather
it either points up less or is more parallel with the ground, or points slightly down towards
the ground upon touchdown.
This reduces the swing time in front of the body and naturally assembles the foot to land
closer to under the ankle, knee and hips, which means stride length reduces and step-rate
increases.
All in all, it’s the coupling of a smoother mechanical interaction of the foot with the
ground, while the foot lands closer to the mass of the body, that results in the immediate
removal of the peak brake force as compared with heel strike running.
In the study, the researchers said that heel strike and midfoot strike runners can reduce
the injurious brake force by shortening stride length and increasing step-rate, but to maximise
the benefit of running more injury-free, why not land in a way where there’s no burst
in colisional impact at all, like in forefoot running, because there’s a long line of
research, which is also linked below the video in the description box, showing that those
who switched to forefoot running had the largest improvements in knee pain and compressive
loading as compared with all other foot strike types, and that's mainly because of the complete
elimination of the peak brake force because key stride parameters engaged by landing with
a forefoot strike, like I said, which are: reduced forefoot inclination or reduced forefoot-lifting
upon and at touchdown, which helps give you better leg swing control by preventing overreaching
of the foot, and a smoother placement of the foot with the ground, may collectively have
a greater influence on sustainably eliminating peak braking at landing rather than just reducing
it by taking smaller steps while heel striking when running because landing behind the arch,
on the heel and then the foot rolls heel-to-toe, still produces a greater jarring force because
of the larger forefoot inclination angle at landing causes the heel pound into the ground
which is still going to produce a brake force peak.
Also, the movement path of the foot when the foot rolls heel-to-toe results in a longer
ground-contact time of the foot which is a determinant strongly associated with abnormal
foot pronation on account of the longer the time the foot spends on the ground when running,
the more time the foot has in being shifted into extreme, abnormal, over-straining positions,
rather than landing in front of the arch, on the forefoot, which nautrally results in
a larger surface area to contact the ground of which impact is also able to spread over
a larger area of the foot, and the movement path of the foot results in lesser ground-contact
time, so the interaction of the foot with the ground is more brief in forefoot running,
because of that, there may be less time for the foot to be pushed away from its neutral
order, and thus, there may be less opposing forces in general in forefoot running as compared
with trying to heel strike more safely by taking quicker, shorter steps.
So the biggest takeaway is that by impact standards, one of the best changes to your
running form may be with forefoot striking because it seems to do more to provide even
better impact protection by completely eliminating the peak brake force and by being more of
a natural facilitator of more controlled foot pronation or sturdier foot step stability.
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Thank you so much for listening and watching.
Have fun out there on the roads and trails.
Bye for now.