WARNING! JAPANESE ASICS WEARING 2:07 MARATHONER HEEL STRIKING PHOTO!!

Nobby,

We could reopen this and do another two hours on the phone.

I agree that a photo can be deceptive and that what happens after the foot hits and how quickly is what matters.

BUT, when you have a photo of someone whose heel is actually on the ground ahead of any of the rest of their foot, I think you're looking at a heel striker, at least in that one stride that got photographed.

On the other hand, there are people of whom I've seen many running photos and their heels never appear to be headed for or on the ground before the midfoot or forefoot. Bill Rodgers and Allison Roe come to mind. Even photos of them at the end of marathons never, in my recollection, showed the sort of pose that we see in Takaoka's photo here. So I'm inclined to think that there's something different going on with him than there was with Billy or Allison.

blahblahblah wrote:

The greatest ground reaction force (GRF) is during toe-off. There are two peaks of GRF during running (and walking). First is heel strike, which in walking is roughly 1.5x body weight. The second is at toe-off, which during walking is equal to heel strike.

Are all GRFs the same, though? Seems to be that the GRF generated during "heel"* strike would result mainly from eccentric muscle contraction, while that generated during propulsion would result mainly from concentric muscle contraction. Wouldn't you want to minimize the former, which is mainly dissipated energy, and maximize the latter anyway?

I'm not sure I see your point.

blahblahblah wrote:

Sir Lance-alot wrote:

The most force/impact occurs as your WHOLE foot is on the ground and your weight is fully supported with your foot/leg right under you.

There are two peaks of GRF during running (and walking).

The point during stance phase which you discuss actually has a lower force than either heel strike or toe-off; it's when the foot in pronating.

(God I love these crazy discussions with the "forefooters" who don't understand biomechanics)

Sir Lance-alot is right on this one, your right about walking but there is no dip in the GRF in running. There is a sudden peak at heel stike for a split second then it rises up to the peak at mid support. In a heel striker there is no intial peak.

Good discussion, and I am glad to see some people agree with some of my points.

I was basing my opinion on observation, and moreso, on certain paper I read. Here is that paper:

http://www1.elsevier.com/homepage/sab/gait/97000386/fulltext.pdf

Review Paper

The biomechanics of running

Tom F. Novacheck

Here are some excerpts which seem to support my contention that Initial Contact of foot to ground does not produce as great as forces on the body as does the mid-stance phase, as the whole foot(or most of it) lands on the ground and the entire foot and leg absorb impact:

1) "Fig. 8. Schematic of a typical ground reaction force (vertical component)

in a runner (rearfoot striker). The first peak is a passive force

peak associated with the shock of contact with the ground. This is

attenuated by the heel pad and shoewear and modified by passive

characteristics of the running surface. It is generally SMALLER and of

shorter duration than the second peak due to active muscle forces (as

depicted in this example). This second peak is centered about stance

phase absorption (vertical dashed line) marking the end of deceleration

(absorption) and the beginning of acceleration (generation)."

2) "Shortly AFTER initial contact, the

quadriceps become dominant producing a knee extensor

moment. The magnitude of the peak knee extensor

moment tends to be greater in running than in sprinting.

This is related to the runner’s greater degree of

knee flexion as the limb is loaded."

3) "This led to inaccurate assumptions. The greatest of

these was that most injuries occur as a result of the high

impact forces at the time of heelstrike. As a result, a

tremendous amount of research has focused on

footwear and the running surface and how those two

factors alter the impact of heelstrike [69–75]. By reviewing

Fig. 8, it is easy to see that the passive forces

associated with heelstrike are smaller and shorter in

duration than the larger, active force phase during the

latter 3/4 of the stance phase [40]. This is not to say

that attenuating the shock of ground contact is not

important. It is essential, however, to understand that

absorption does not occur instantaneously like a bowling

ball landing on a cement sidewalk! Several different

tissues dissipate this force over time during the first half

of stance phase (as previously discussed) thereby minimizing

the shock to the body [40]. These tissues include

1. Achilles’ tendon

2. Plantar fascia

3. Quadriceps mechanism

4. Hip abductors "

4) "It now seems more likely

that most of the chronic injuries from jogging are

related to the high forces that occur in mid- and late

stance [than from forces at initial contact]".

5) "Peak forces(on the achilles tendon) do not occur at initial contact, but in midstance.

They are generated by the powerful contraction of the

gastrosoleus—not by the shock of initial contact with

the ground. These injuries are due to the active muscle

forces of midstance not to the passive impact forces at

the time of initial contact."

So this guy's heel might touch first, but it might just brush the ground as he quickly rolls onto his whole foot, which might not change impact much from somone who touches midfoot first before their whole foot lands on the ground.

my friend abdi heel strikes

Sonny Boy wrote:

Are all GRFs the same, though? Seems to be that the GRF generated during "heel"* strike would result mainly from eccentric muscle contraction, while that generated during propulsion would result mainly from concentric muscle contraction. Wouldn't you want to minimize the former, which is mainly dissipated energy, and maximize the latter anyway?

I'm not sure I see your point.

Actually the GRF at heel strike doesn't come from eccentric contractions, it comes as a result of gravity. GRF is the force from the ground in response to your body dropping onto it. What, is that Newton's 3rd law? For every action there is an equal and opposite reaction. It's not equal to your body weight b/c you're "falling" from some height. The eccentric contractions that occur during gait are to control motion of the joints. Your quads activate and have an internal extensor torque (moment) in order to keep your knee from flexing too far (it flexes a bit at impact).

Not sure why you would want to maximize the concentric contractions anyway. Running is mostly a passive motion, a control falling of sorts. You just happen to bring your leg up and around in order to catch yourself each time you fall over and over and over again. The eccentric contractions are what make you sore after a race, so you'd want to increase your eccentric strength.

im a heel striker and i just pr'd this weekend at washington in the mile...4:02

i can also run 49 flat in the 400 with the same form.

blow it out thine ass

aa

I just saw the actual video of this guy finishing the marathon. He is yelling "Where are all the white women at?" as he crosses the line. Incredible stuff.

koroibos wrote:

Sir Lance-alot is right on this one, your right about walking but there is no dip in the GRF in running. There is a sudden peak at heel stike for a split second then it rises up to the peak at mid support. In a heel striker there is no intial peak.

You're right sort of. There will be an initial peak with a heel striker. It just won't dip down much if at all before rising again as the person moves into toe-off and pre-swing.

Depending on the person, there can be a small dip in the GRF, but in most cases it is either even or higher at midstance.

The point is that GRF is greatest at toe-off.

I re-read what Sir-Lance-alot wrote and I agree that it really doesn't matter if elite heel-strike or not. I'm sure that they are using the most efficient form possible for themselves, i.e everybody's different.

I think you are getting mixed up between running and walking. All what you say is true regarding walking but not running. While walking is controlled falling as the body acts like an inverted pendilum. Running involves propulsion off the ground at toe-off. It is more like a jump as you are off the ground during the flight phase, so to have a longer flight phase (not always good) you need a strong concentric contraction.

Also muscle are acting eccentrically from heel strike as the muscle are slowing down the movement. It is not due to just gravity, the forces are due to the body decelerating what ever velocity the body has at impact, much of which is greater due to horizontal velocity and angle leg has at impact.

Why would people have a dip down at midstance? I ask this because I had a small dip in the horizontal force on one leg, could never find any where this was reported or explained. It was as if there was a brief moment where the braking force was reduced. I can't see why GRF would be greatest at toe-off.

koroibos wrote:

I think you are getting mixed up between running and walking. All what you say is true regarding walking but not running. While walking is controlled falling as the body acts like an inverted pendilum. Running involves propulsion off the ground at toe-off. It is more like a jump as you are off the ground during the flight phase, so to have a longer flight phase (not always good) you need a strong concentric contraction.

Also muscle are acting eccentrically from heel strike as the muscle are slowing down the movement. It is not due to just gravity, the forces are due to the body decelerating what ever velocity the body has at impact, much of which is greater due to horizontal velocity and angle leg has at impact.

I stand by what I say about controlled falling. In running you are still controlling a fall but it's from a greater height (which you cause through concentric contractions, then control the impact through eccentric ones). Not only do you need a stronger concentric contraction, but you need greater range of motion through the hip, knee, and ankle.

If we are talking about vertical peak ground reaction forces, it is due to gravity. When you talk about horz. velocity and the angle of landing you bring in A-P shear forces. They relate, but I was under the impression that we were talking about vertical forces.