In running, not all impact forces are bad. There are some impact forces the body can easily
withstand. One such force always produced during running is the ground reaction force. This is just
a basic force produced at landing during running. Faster runners, even if they land with a forefoot
strike landing pattern, tend to generate a larger ground reaction force than slower runners,
but this force still usually falls within a relatively safe range of tolerance. Impact forces
in running may become very problematic when they exceed tolerance that the muscles can't absorb,
and from this, can easily give rise to all kinds of injuries. Impact can also be very damaging if
it's a peak impact or a peak pressure or a peak impulse. When you see the word 'peak' in front
or after the words impact, pressure, force or impulse, the word peak means there's a burst of
high impact that exceeds normal. There's more full blunt impact that exceeds a certain threshold that
can easily grind down the lower body when running and is largely to blame for more severe injuries,
like long bone injuries. Peak impact forces in running arise when there's a lot of opposing
forces at work. One consistent example of where we see the most impact peaks produced in running
is in heel strike running, not so much in forefoot strike running. This is why heel strike runners
tend to suffer more long bone injuries, such as a femur fracture as compared with forefoot runners.
A collective of studies, which are linked down below this video in the description box, have used
what's called the 'shockwave chronic overload model' to explain how the chronically higher
impact peaks in heel strike running contribute to long bone injuries, namely a femur fracture.
Based on this model, the evidence shows that at heel strike when running, the mass of the body
abruptly grinds to a crashing halt and remains in a prolonged break phase at landing. This
also means the mass of the body gets loaded onto the leg for an extended period of time.
This is because at heel strike, there's often an over-extended leg with an unbent knee. This
creates a larger distance separation between the mass of the body and initial foot strike position.
In consequence, an impact transient peak is produced which is accompanied with shock loads
that are measured in the long bones, including the femur. The shock loads travel up the
musculoskeletal system as a propagation shock wave and continue to propagate with each subsequent
step during heel strike running. According to the shockwave chronic overload model, the impact
burden of doing all of this is the cumulative strain from the chronic overloading from the shock
loads and propagated shock waves produced at heel strike when running ends up tipping the balance
between micro-damage formation and its removal in the femur. The increases in micro-damage
formation in the femur during heel strike running correlates with an outsized risk for bone stress
and fracture on multiple sites on the long bones, like the tibia and the femur. To this point,
the fact that there's research fully addressing how heel strike running may directly cause a femur
fracture through a shock wave chronic overload model, confirms that there are impact variables
unique to heel strike running that cause heel strike running to be one of the leading causes of
running- related long-bone injuries. In contrast, there is no shockwave chronic overload model
for forefoot running because there is no shock wave produced in forefoot running. Now, that's
not to say that there's never been a long-bone injury incurred by a forefoot runner. Of course,
there are additional contributing factors to long-bone injuries in runners, such as bone
density issues being one; upping your mileage too soon when you are nowhere near conditioned enough,
is certainly another factor. However, it's really worth mentioning that femur fracture
is incredibly low, if not, really unheard of in forefoot running and this is because related
research on impact mechanics indicated that in a forefoot strike landing during running there's
an automatic removal of the impact peak transient force responsible for the propagated shock wave
and that right there is perhaps the most frequently cited evidence in support of the
impact protective nature of forefoot strike running which also fits what can be observed
in general is that you don't really see many forefoot runners cracking their femurs as
compared with heel strike runners, but you could argue that a heel strike runner could just wear
a running shoe with thickly padded heels. Doing so won't fix anything in this case for two reasons:
for one, heel cushioning has been shown to be ineffective because surprisingly low magnitudes
of the shock-wave at heel strike when running was enough to produce the chronic overloading
found to be a big contributor to femur fracture. Secondly, increases in under-heel cushioning
have been consistently found to have the main effect of increasing the amount of downward force
at landing, regardless of foot strike pattern. Basically, the thicker the underfoot cushioning,
the harder the foot plows onto the ground during running, while at the same time,
what's so interesting is that the body actually perceives the forceful foot-strike intensity as
much lighter than it actually is. This phenomenon is called 'perceptual illusion' and it's really an
unintended consequence of running in thickly cushioned running shoes which is why some
forms of impact tends to be chronically higher in most runners who run in thickly cushioned
running shoes versus most barefoot runners -- the article about that is linked down below the video
in the description box as well. Moreover though, so far, published studies have really failed to
show how cushioned running shoes can make heel strike running safer which is why with
all the advancements in cushioned materials in running shoes and running shoe technology overall
these forms of footwear really haven't put a dent in the high injury rates incurred by most runners.
This is why making adjustments in your foot strike mechanics may be a much better long-term course of
action to take, in that, forefoot strike running is seen as a big positive in having a big role to
play in preventing landing intensity from becoming too aggressive thereby potentially doing more
to safeguard the long bones. To account for this, landing further away from your heel when you run
like in a forefoot strike landing pattern allows for better management of these stride
parameters responsible for impact production such as engaging a forefoot strike landing
when running instantly engages a more bent knee or increase the flexion at touchdown through this
you are prevented from overreaching too far in front of you with your foot at touchdown
you end up with a lesser overstrike angle this allows the impact transient peak to be eliminated
and you are also going to get a much lower rate of the brake force that together prevents
the propagated shock wave most responsible for a femur fracture because the lung bones are far less
likely to overheat since the body isn't coming to a grinding halt for an extended period of time
like it so often is in heel strike running and there really is nothing new about the
way forefoot strike running assembles other stride parameters that help you land much softer
on that note i just thought it would be very important to highlight one of the many advantages
forefoot running may have over heel strike running in that forefoot running may do more to shield the
long bones from high impact and that forefoot running may really sustain much better long term
for the prevention of certain impact-related injuries not to mention that evidence-wise there's
a lot of hard evidence showing that heel strike running does not consistently prove its full worth
for improving the odds of reducing major injuries all you have to do is follow the data trend
showing the runners who get hit the most with the most severe injuries more frequently and
you will see that an overwhelming majority of these runners have one common denominator they
heel strike when they run forefoot runners really aren't getting their knees replaced
or pins and plates installed in their femurs at all and even if they are it's absolutely nowhere
near at the rate to that of heel strike runners in that regard i posted a link to a video that i did
showing what a proper forefoot strike looks like because some make the mistake of landing too high
up on their toes or landing big toe first a proper forefoot strike landing is actually a much flatter
foot placement at landing almost like a midfoot strike and initial ground contact is also made
towards the lateral border or towards the outer side of the forefoot which is all shown up close
and in slow motion and in normal speed in that video i hope you've enjoyed this video if you
did feel free to hit the thumbs up button as well as the subscribe button if you haven't already
where you will stay more informed on heel strike running versus forefoot strike running
thank you so much for listening and watching have fun out there on the roads and trails bye for now