This discussion has been going on at the Supertraining board between Dr. Yessis and Barry Ross. Interesting.
Barry wrote:
<<Hi Dr. Yessis,
Here are my matching responses, as you requested,to your questions:
(1) Yes, limb speeds can be the same. You can see this in action by
going to www.bearpowered.com/resources, then clicking on The Saga of
2 Runners. What you will see is that both runners are landing at the
same time, stride after stride, yet in a 100m race the faster of the
two is faster by 1 meter per second faster. If you watch the grounded
foot of each runner, you will see that the faster one’s foot leaves
the ground increasingly earlier than the other. This allows more air
time to reposition his leg for the next stride. Weyand’s study
mentions precisely what you see in the video, “Faster runners applied
greater forces during briefer contact periods, whereas slower runners
applied lesser ground forces during longer contact periods.”
The faster runner needs no more time to reposition limbs then slower
runner uses.
Interestingly, stride frequency does increase (" The large
sensitivity of top speeds to small differences in the mass-specific
support forces applied to the running surface resulted from the
positive effect of support forces on maximal stride frequencies."
Weyand, et al.). What is the cause of the faster stride frequency?
“Stride time (measured in s) was defined in accordance with Heglund
et al. as the time between consecutive footfalls of the same foot”
and “Stride frequency was determined from the inverse of the total
stride time (1/total stride time).”
Stride frequency, as determined above, improved because of the
shorter contact time of the faster runner. All of this is driven by
mass specific support force.
In answer to your question regarding distance covered, yes the faster
runner is covering more ground as he easily pulls away, but he
doesn’t have to move limbs faster to do so. It’s not individual limb
speed that’s critical, it the speed of the body that must be
considered.
(2) You are correct in saying that force equals mass times
acceleration.
Where the problem lies for most is in recognizing that gravity pulls
the runner back to the ground and would continue accelerate the
runners mass until it hits terminal velocity (which won’t happen to a
sprinter, so it’s not really in issue here). In other words, the
airborne runner is now no different than any falling, accelerating
mass.
The opposite side of the amount of force created by the accelerating
mass of the runner striking the ground is what ground reaction force
plates measure. Newton’s 3rd Law states that this measured force must
be equal to the force the runner hits the ground with. That force is
equal to 3 times bodyweight or more. The runner did not create this
force through chemical muscle power, but instead by merely hitting
the ground as a falling, accelerating mass. That is pure,
unadulterated physics.
Ground support force is the amount of force the runner must apply to
the ground so as not to collapse from the impact (support) and to
take maximum advantage of the force that will be returned by the
ground (Newton’s 3rd law). This force applied by the runner is
derived primarily isometrically, so there is minimal change in muscle
length as well as minimal limb movement in creating force.
How does this equate to greater strength and less mass?
Let’s assume that our runner is 150 lbs and hits the ground with 450
lbs of force against the mass of the earth. The earth is going to
return 450 lbs of force against the runner’s mass. The runner’s force
is not going to move the earth’s mass but the earth’s force is
certainly going to move the runner’s mass since it is 3 times greater
than the mass of the runner. Now, up the ante with an elite sprinter
creating force equal to 5 x bodyweight and that sprinter is going to
be moving a lot further down the track. How can we know this? Because
Weyand’s study showed that, “Average support forces of runners
applied to the running surface at top speed were systematically
higher for faster runners.”
(3) After digesting the above, it should be clear that strength
doesn’t create ground reaction force, but rather accelerating mass
does. Ground reaction is just that, reaction to the force hitting it.
Since support force is largely isometric, joint actions are not the
prime points of focus for improvement. In addition, it should be very
clear from watching the video of the 2 runners that knee flexion is
minimal and therefore could not create the massive forces measured by
GRF plates. This goes back to the “test” I proposed to the members of
this forum.
(4) The deadlift is not better than its closest neighbor, the squat,
as far as maximizing strength, but it has some essential factors that
make it more efficient and effective for the training required. I’m
not
going to go into all those reasons. That being said, specific joint
action is not where strength is displayed for all of the reasons
stated above. Specificity of training for running is not centered
around joint movement but on increasing isometric strength, bone
density, muscle density, tendons etc. for increasing support force to
offset gravity. All of these are necessary as support and not the
creators of force. Ballistic lifts don’t cut it here either.
(5) While the Pose method at least mentions gravity as relevant, it
barely touches on the importance of it. The system also relies on
training elements of running by means that simply don’t work. I
passed on the Pose long ago.
It’s quite simple to explain how vertical and horizontal influences
work together in sprinting (Interesting how that question is always
framed as how vertical can be responsible for horizontal. How about
we reverse the question: How does one get in the air by pure
horizontal forces?). The beginning of a run must be dominated by the
horizontal because it is necessary to use chemical muscle mechanical
work to overcome inertia by pushing the mass forward rather than
upward. As speed increases, the runner begins to elevate in order to
allow gravity to begin the work described above, that is, using the
force of gravity to create ground reaction force as well as creating
and storing elastic energy used for impulse in the vertical
direction. The vertical direction doesn’t mean straight up, it means
that the runner will use a vector that allows them to trade the high
metabolic cost of chemical muscle mechanical work for the lower cost
of ground reaction force and effective impulse from elastic energy.
The horizontal force at take off is equal to the braking force at
touchdown, assuming no wind. This is true because of Newton’s 3rd
law. The braking action is critical in maintaining the horizontal
portion of the vector. Here’s why: The runner is traveling at a high
rate of speed while in air. At toe down, mass is just behind the
grounded foot. The foot stops moving forward at that point, but the
torso keeps moving horizontally, especially since the majority of the
mass is around hip height which creates a catapult-like effect. If
one drives a car at 25 miles per hour, but foolishly forgets to put
on a seat belt, what happens if the car hits a wall? The seatbeltless
person continues to move horizontally at the same speed the car was
moving until they hit something solid.
As mass crosses over the grounded foot, ground reaction force and
impulse from the elastic energy created from eccentric contraction
puts the runner back into their running vector. Ultimately, the
runner slows down as muscles tire from the isometric work and can no
longer create and release sufficient elastic energy.
(6) Your statement here was: “In relation to ground reaction forces,
you state that they are greatest halfway through the support stance
time and mostly gone after two-thirds of this time.”
In all due respect Dr. Yessis, this is what the measurements show and
there is no way to get around it. In fact, if you go back to
www.bearpowered.com/resources and click on Force Plate Fellow (circa
1970’s or so and found on the internet), you will clearly see that a
ground reaction force plate only shows a measurement of force when
force is applied to it. It is also clear that merely crouching down
for the counter motion jump creates force because the body is
accelerating towards the plate (mass x acceleration=force). When the
man begins to move upward, force begins to disappear because he is no
longer accelerating downward. At the moment just before he lifts off
the ground, how much force is being applied to the ground? Virtually
no force is measured so there is virtually no force applied to the
ground when the jumper jumps. Isn’t this where peak push off forces
should show if they exist?
In contrast, look at the 1 sec point where he begins toe down.
Within .2 seconds of toe down, force peaks, then starts to drop. This
is exactly what I described in (3) above. The answer to your
question, “How does this leave any force for the push-off?” is clear:
It doesn’t leave any force for push off because there is no force
applied to the ground at push off. It also means that you’re were
absolutely right when you say, “If this is true there is no need for
ankle extension.”
What you’re seeing as ankle extension is caused by the reaction of
the previously grounded foot to the eccentric contraction of the calf
muscles and Achilles tendon as the man moves up from the counter
motion. The same reaction can be observed by pulling one forefinger
back as far as possible with the other forefinger, then releasing
it. It isn’t chemical muscle power that snaps the just-released
finger forward, just as it isn’t chemical muscle power that extends
the ankle at toe off. Pictures aren’t proof of push off either
because they don’t show force.
Proof that force is created at push off must be shown clearly on GRF
plates if that concept is to viable for training. Until that
proof is made available, exercises claiming to help create force at
push off should be set aside.
(7) I did not mean to imply that knee extension is the key factor in
supplying the speed in running. A small bend in the knee is necessary
to activate the spring part of the spring-mass model. A straight leg
would not allow for an effective spring action. It is the spring-like
action and GRF that supplies the speed in running.
Weyand truly understands running, as would his peers attest along
would the multiple citations of his work in the research papers of
others. Not one locomotion scientist has come forward to contend
against the research paper in the 6 years since publication of the
paper we’ve been discussing. Weyand’s paper is ground breaking in its
analysis of running speed, mass-specific force, the effects of force
application, and much more.
And finally, there is always a danger in using pre-suppositional
thinking in order to review the merits of a “new” proposition. All of
us should be aware of that when we examine anything new, since we’ve
all been guilty of relying on something we thought to be true as the
bench mark for looking at the efficaciousness of a new approach. It
took 3 years for me to get through the fog of my pre-suppositions
regarding sprinting and sprint training before I could fully
understand the vast amount of research regarding the spring-mass
model and a strength training routine that fits within in the
trainable aspects of the model.>>>
Hello Barry
I’ve been out of town and apoloogize for the delay in responding.
Early in this discussion I mentioned the need to connect the dots
between the Weyand study and how it is applied. I’m sorry but I
must ask it again because your responses state many truths but not
how they fit into the discussion.
For example, in RE #1 there’s nothing new here — the information
is accurate but not the conclusion. More importantly it does not
address limb speed Speed of the body is dependant on limb speed and
the push-off. Simply compare a marathoner to a sprinter. Leg (limb)
speed is much different. This is pure physics, not opinion. The
formula for speed gives you the answer. Speed (more accurately
velocity) equals distance divided by time.
You go to great lengths talking about stride length and frequency
which are related to speed but not to the question asked. This only
clouds the issue.
RE #3 This is where a major problem exists. Yes a runner’s body is
subject to gravity, but has little to do with it’s speed. It plays
a minor role in comparison to the forces produced by the body.
For example, the vertical displacement of the CG in a sprinter is about 4
cm --about 1 inch. A free falling body dropping 1 inch cannot
generate the forces produced.
Your introduction of isometric force production is new and quite
intriguing as it may disprove what you have been saying. Do you mean
to say that when the foot hits the ground the limb muscles undergo
isometric “contraction”? What happened to the eccentric and
concentric forces that are responsible for the spring model that you
previously espoused? Also note that the foot is in contact with the
ground for about one hundredth of a second, --certainly not enough
time to generate much isometric force.
Later on you state it is the support force that is isometric. This
is partially true but does it also provide the push-off force to
which you alluded earlier?
Your use of Newton’s reaction law is also quite limited. By the way
you should know that I taught biomechanics for about 40 years and
am quite familiar with the laws and their application. Your
application of this law is flawed because you only consider the
vertical forces.
In # 6 you admit there are horizontal forces. Before it was only vertical, thus my question on how it is converted to horizontal. These forces interact and produce a reultant force, not two separate forces as you imply. And it can ONLY be applied at push-off if Newton’s law is to be in effect. But then you say it is non-existent at pushoff since there are no vertical (I guess) forces at this time. You still have not answered how the vertical is converted to horizontal or if it is, how it is generated. This is the crux of this discussion and is what must be addressed.
I need an explanation of the way you use braking force. How can it
be equal to horizontal force at take off? Sprinters minimize
braking forces as much as possible. Zero force is the best.
Also important at this time is to consider how the leg gets under
the body. Or since, in your view, what the legs do while airborne
is inconsequential why not have the runners land on the heel well in
front of the body, as many sprinters and even more marathoners do?
If we are to believe you, this would create even higher braking
forces which would then produce a stronger push-off.
Your last sentence in # 5 shows how you are erroneously concluding
the information that you have been presenting. We read that “…the isometric work (and) can no longer create and release elastic energy”. What happened to the tendon-muscle complex and the spring model based on the eccentric-concentric “contraction”?
This is what I mean about sticking with the issues and not grabbing
bits of correct information and then trying to work them into a
seemingly scientific explanation.
RE # 6 I never challenged the force plate readings. I challenge the
way the data was interpreted and used by you or perhaps I should say
Weyand because you learned this from him. What has been lacking in
all the discussions is the horizontal component which most force
plate platforms do not record. But yet everything in your
discussion was explained by the vertical forces. This is what I
challenged and if someone truly understands running it should be
obvious that horizontal forces are much more important than the
vertical. And I don’t refer to your use of horizontal when coming
out of the blocks. This has nothing to do with the issue at hand.
Being a track coach I’m surprised that you would not strongly
question the obvious lack of explanation for horizontal speed.
Simply asking yourself why sprinters use spikes should raise your
doubts about using this study and the many erroneous conclusions
that have been drawn from it.
You state (in # 6) that there is no force applied to the ground at
push off. This shows you do not believe–or understand-- that there
must be horizontal (with a vertical component) forces at takeoff.
If what you say is true you probably have the sprinters run without
spikes. Also I did not say ankle extension is not needed. As you may some day learn it is a key force producing action.
I am not surprised that no one has challenged the results of Weyands
study. It takes a strong understanding of what constitutes running
from a biomechanical and kinesiological perspective,-- something
that to date I have not seen. As I mentioned earlier, you should
read my book, Explosive Running, for a full understanding – at
least based on the latest sound, and not partial, information that
has been discussed.
You keep stating how Weyand truly understands running and how his
peers would attest. If this is so why do we not read some simple,
accurate, factual explanations of what occurs in the running stride?
Regards,
Michael Yessis, Ph.D
President, Sports Training, Inc.
www.dryessis.com
(760) 480-0558
PO Box 460429
Escondido, CA 92046
~~~~~~~~~~~~~~~~~~~