When it comes to runners' knees, there’s a strong correlation between knee injury and
certain impact force components unique to heel strike running.
For example, compressive loads are produced in larger amounts in heel strike running because
of the extended brake force at touchdown as compared with forefoot running, of which the
knee bears the expense of this impact that’s produced in heel strike running.
In forefoot running, the brake phase at touchdown persists shorter in duration.
In fact, the brake force in forefoot running is small enough to avoid the heavy compressive
loads on the knee, which is one reason forefoot running can be very effective in reducing
knee injury in a sustainable way.
Another big reason heel strike running may contribute to knee injury is that the heel-to-toe
rollover motion of the foot shortly after heel strike may place additional stress across
the knee because when the entire weight of the body transfers over the entire foot when
the foot rolls heel-to-toe during stance usually accompanies a different pressure loading pattern
over the foot as compared with forefoot running of which in forefoot running, at touchdown,
the foot interfaces differently with the ground which why the pressure loading pattern over
the foot is different in forefoot running than in heel strike running.
But in heel strike running, when the foot rolls heel-to-toe, it was found to cause extra
loading on the forefoot which in turn was found to cause more intense and prolonged
pronation of foot in order to attenuate or absorb the excessive loading on the forefoot.
Basically, the foot was forced into extreme positions, which means the foot pronated more
than normal in efforts to minimize the overloads on the forefoot that was induced by the heel-to-toe
rollover motion of the foot.
This was found to increase rotational stress on the knee.
In general, the purpose of pronation of the foot during stance when running is it unlocks
the smaller joints of the foot/ankle complex, allowing the foot to become a mobile adaptor
and shock absorber.
Essentially, foot pronation during the stance phase of running is the one of the body’s
natural shock absorbing mechanisms, but just like anything else, if foot pronation shifts
into extreme positions, out of tolerance, it can be counterproductive because abnormal
pronation may produce opposing forces on the foot, ankle, shin and knee because overpronation
of the foot can have a ripple effect up the leg in that its been known to increase bending
strain on the achilles, torsion on the shin and rotational stress on the knee, which seems
to the case in heel strike running such that increases in mechanical stress on the knee
and therefore, increases in knee injury in heel strike running, may reflect forceful
pronatory engagement that occurs to counter more pressure stress on certain areas of the
foot when the foot rolls heel-to-toe when running.
Where we dont really see this over-pressure induced over-pronation is in forefoot running
because as i just touched on briefly, the foot configures differently with the ground
in forefoot running in that there’s no heel-to-toe rollover of the foot, rather the foot moves
forefoot-to-heel which results in a different pronation pattern of the foot than in heel
strike running, and this difference in foot pronation in forefoot running may be more
protective on the knee.
This is all because the pronation pattern of the foot in forefoot running was found
to allow greater control of the foot until the heel lowers to the ground, and may allow
the arch to contribute to shock absorption more fully by allowing it to lower and become
more mobile, so the source of extra impact protection, which is the arch, in forefoot
running, may help prevent impact from being muplited up to the knee.
Another advantage of how the foot interacts with the ground at touchdown in forefoot running
that may help safeguard the knees is that landing with a forefoot strike instantly results
in a much larger foot contact area which disperses pressure on a wider surface area on the foot,
therefore pressure can be absorbed more sufficiently without creating dangerous over-pressure points
on the foot.
This may result in less pronatory response and may enable pronation to stay within a
more safe range which in turn may reduce the transfer and spread of rotational stress on
the knee.
Last but not least, in forefoot running, there’s a shortened ground-contact duration and so
there may be less time for the foot to shift into extreme, overstraining positions as compared
with heel strike running which is associated with much longer ground-contact time and longer
pronation duration.
So essentially, forefoot running may do more to sustainably lift stress off the knee, not
just by naturally reducing compressive loading on the knee, but by limiting mechanical strain
on the knee on account of the motions of the foot in a forefoot strike landing and how
it influences the way pressure travels and spreads over the foot, may not be a source
of knee injury like it seems to be in heel strike running.
On that note, I posted links in the description box to other videos Ive done on the other
ways heel strike running may increase the risk of knee injury as compared with forefoot
running.
I’ve also linked in the description box to the data referenced in this video.
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Bye for now.