Posted In: Blog Discussion

• Member
richard-703 on #59455

Dan,
I know about the units, I usually work in SI.

If the force during a lift is at some time greater than that strictly necessary to lift the weight, then the force plate will measure this (we weren't talking about work, I know gravity is a conservative field). My point was that you don't need to lift triple bodyweight in order to record triple bodyweight forces.
The fact that you can measure them during a sprint is an example of this.

I think it is misleading to imply that one needs to do triple bodyweight one legged squats to equal sprinting forces.

Participant
bear on #59456

Dan,
I know about the units, I usually work in SI.

If the force during a lift is at some time greater than that strictly necessary to lift the weight, then the force plate will measure this (we weren't talking about work, I know gravity is a conservative field). My point was that you don't need to lift triple bodyweight in order to record triple bodyweight forces.
The fact that you can measure them during a sprint is an example of this.

I think it is misleading to imply that one needs to do triple bodyweight one legged squats to equal sprinting forces.

It would be helpful to reread my post. I said that force could exceed 3 times bodyweight. If you want to knock off the individuals bodyweight, that's not a problem.  Just load a 150 lb runner with 300 lbs and have them try it. The point being made is that the runner is not capable of producing the amount of force measured. If that's the case, and it is, then where is that force coming from and how does it affect the runner?
Also, ground reaction force plates measure forces in 3 directions and up isn't one of them.

Member
richard-703 on #59457

Bear,
Have the 150 lb athlete try what? What exactly do you claim they need to do to record the force you want?
I'm interested in producing forces that "I'm not capable of producing"?!

In what 3 directions do your plates measure forces? If they are non-redundant (orthogonal) then one or more must have a projection on what I call "up".

Participant
bear on #59458

Bear,
Have the 150 lb athlete try what? What exactly do you claim they need to do to record the force you want?
I'm interested in producing forces that "I'm not capable of producing"?!

In what 3 directions do your plates measure forces? If they are non-redundant (orthogonal) then one or more must have a projection on what I call "up".

Hi Richard,

3 axes: transverse (X), anteroposterior (Y), and vertical (Z). The vertical measurement is the return of force applied to it. If you stood on a grf force plate then squatted down, the plate shows force being applied because your mass is accelerating downward. If you jumped up, the grf plate would not register force application.

Member
richard-703 on #59459

Hi,
I reread some of your posts. You say that "force plates ignore vectors, they simply measure force". I claim that force IS vector, so if you are measuring it (3 components apparently), then you are not ignoring it.

I think your example of standing on a plate and then squatting down, just tells me when you "zero" your measurement. I would like to call it zero when nothing is on the plate.

If the large force is over a short time and short path, then the overall power isn't extreme.

What peak forces will you measure if someone does some "snappy" 1/4 squats on your plates?

Participant
bear on #59460

Hi,
I reread some of your posts. You say that "force plates ignore vectors, they simply measure force". I claim that force IS vector, so if you are measuring it (3 components apparently), then you are not ignoring it.

I think your example of standing on a plate and then squatting down, just tells me when you "zero" your measurement. I would like to call it zero when nothing is on the plate.

If the large force is over a short time and short path, then the overall power isn't extreme.

What peak forces will you measure if someone does some "snappy" 1/4 squats on your plates?

Hmmm, I'm not the force plate so I'm not ignoring anything. It's not an issue of what you claim, the force plate's function is to register force applied to it. Force = m x a so unless there is an accelerating mass the force plate won't measure it.

Obviously then, if you did a "snappy" 1/4 squat on the plate it would register greater force than if you did a leisurely 1/4 squat.

Member
richard-703 on #59461

Barry,
The strain gauge should measure the force due to gravity acting on the mass.
It just comes down to how you zero the setup, we can go round and round…

Bottom line, do you think that some special forces are in play during sprinting that aren't easily understood?
That can't be found in other activities?
Are there a lot of people (researchers) who claim not to understand it? Please no more F=ma, I work in science (that's why I'm interested).

Participant
Daniel Andrews on #59462

That "special force" is called a leg spring(a hookean spring).  Who are these researchers that don't understand it?  I don't know of any researchers who don't.  F=ma is everything, without it there is no biomechanics, much less mechanics at all and the physical world around us just sort of doesn't exist then.

The force platform is the only thing you can't trick, there is the possibility of interference from noise.  If you suddenly change your com while in contact with the FP it will register the changes in force along all 3 axes as Barry stated.

Member
richard-703 on #59463

Dan,
I'm very familiar with the basic physics that you guys keep quoting me.

Barry's posts talk about the forces occuring during a sprint being larger than an athlete can produce (yet the athlete produces them).
I'm asking if this is something that he (or others) don't understand. You say it is well understood, fine. It sounded strange in his post.

I would be surprised if the measured forces aren't understandable. I also imagine that similar forces could be produced during other activites.

Participant
bear on #59464

Dan,
I'm very familiar with the basic physics that you guys keep quoting me.

Barry's posts talk about the forces occuring during a sprint being larger than an athlete can produce (yet the athlete produces them).
I'm asking if this is something that he (or others) don't understand. You say it is well understood, fine. It sounded strange in his post.

I would be surprised if the measured forces aren't understandable. I also imagine that similar forces could be produced during other activites.

Richard,
It's not me that doesn't understand, it's you. Once again, It's not a special force, it is force that the athlete does not produce volitionally. It's not force created by pushing off the track. It is the body hitting the ground that produces force. If it was created by muscle mechanical power then the same athlete should be able to do the same thing in the weightroom, thus my analogy. No person could volitionally create the amount of force (in the time allowed) measured during high speed running by using concentric contractions, nor could they do it repetively. This negates much of the current training concepts and methods.

Similar forces occur in every sport where athletes run or jump.

BTW locomotion experts use force plates to measure ground reaction force.

Dan,

The force created is not from the leg spring. The leg reacts to the force by producing potential elastic energy, which aids the spring behavior, thereby reducing the metabolic cost of running.

Member
richard-703 on #59465

Barry,
Thanks for the clarification. If that's all it is then I do understand…

So please elaborate on why you feel this negates certain training and what you can do about it.

Participant
Daniel Andrews on #59466

Barry:

I wasn't saying the leg spring creates the force.  Just addressing his "special force".

Participant
bear on #59467

Barry:

I wasn't saying the leg spring creates the force.  Just addressing his "special force".

Dan,

You clearly stated that I was an idiot and had no business being in a special forces unit unless I learned how to only drink water from a special spring and that I should stop using street hookeans for evil purposes.

Maybe you didn't say it like that but I know that's what you meant.  :smilegrin:

Keymaster
Mike Young on #59468

I don't think I'm off course at all, let alone "woefully". Where did I say that the direction of the force vector does not matter?

By saying that technique doesn't matter it is being taken by myself and others that the direction of the force vector does not matter. It is the positioning of the limbs with respect to each other and the ground that determines the direction (and to some extent the magnitude) of the force vector. In my opinion, stating that technique is unimportant and the direction of the force vector is important are completely incompatible statements. If all we do is build a big engine (to produce more force) and not concern ourselves with the kinematics at all then we're going to get weightlifters who can apply large forces but can't run.

Chemical work is the volitional contraction of the muscle by the athlete.

That's your own terminology but that's fine. You'll never find that definition in a text book. For the purposes of this discussion this semantical issue doesn't matter much. I'd prefer to call this a voluntary contraction. For what it's worth, greater force can be produced when the forces generated involuntarily (reflexively) and voluntarily are summed.

An eccentric contraction does not require the brain to send a chemical signal to the muscle to contract.

This is partially incorrect. It should be worded that the body CAN produce eccentric contractions involuntarily in response to a rapid stretch or force applied. Eccentric contractions can also be produced volitionally however. It's also important to note that involuntary eccentric contractions will not produce as great a force as a combination of the reflexive contraction and the voluntary contraction. Also, I'd like to point out that it's possible to increase the reflexive component by positioning the limbs in such a way that they are elastically / plyometrically loaded in the most appropriate manner. Finally, I'd like to point out that while these actions tend to be more metabolically more efficient than concentric contrations, there is still a metabolic / chemical cost of these contractions. There is no such thing as "free" energy.

BTW this thread topic was about whether or not technique training is necessary, not about force vectors.

As I said before, I do not think the two topics are mutually exclusive. In fact, I don't think they can be separated at all. Technique affects sprinting / running on 2 major levels: functional capacity and direction of force application. When I refer to functional capacity I'm speaking of placing the body in positions where it can best produce force and most take advantage of the elastic response that occurs as a result of the eccentric loading during sprinting.

The second major factor where technique plays a role in sprinting is by affecting the direction of the force vector. This happens / is possible because the positioning of the limbs with respect to the body and the ground will dramatically affect the direction of the force vector. In an extreme example, if someone were to somehow overstride so that their ground contact position was 2 feet in front of their center of mass, the initial direction of the force vector is going to be primarily backward at ground contact in the opposite direction the athlete is trying to run.

In the shot put analogy above, the thrower can make the adjustments to their throwing vector because they have the time to do so. The surface used on that day does not change between throws. It's a bad analogy, period.

A couple things here. First, I can tell you with 100% confidence that there is a large elastic loading of the lower extremities and trunk musculature in the shot put. As USATF's shot put biomechanist for the past 5 years I can tell you that without a doubt there are reflexive / elastic responses that need to be set up by prior actions. For example, if the flight phase is too low / flat the athlete will not be able to elicit the elastic response that is ABSOLUTELY NECESSARY for big throws. While not all athletes can handle this eccentric loading, every guy in the world whose thrown 70+ feet can, and for these athletes it is actually beneficial to increase the height of the flight phase (within reason of course) to enhance the plyometric loading effect.

Second, does the surface change for running? You made some comment about this and I don't know what you're talking about. If we're speaking of track athletes, the ground that athletes run on should be as consistent and regular as a shot put circle. I didn't see how this could even come in to play….especially with sprinters.

Most elite throwers will tell you (lesser throwers who are throwing with less velocity likely differ) that after the front foot touches down that they can't adjust anything. If they haven' set up the throw prior to the front foot touching down then there's very little hope for recovering from faulty prior movements.

But, preparing during flight time in the sprints? How does one "prepare" the limbs to be in the best position while traveling at speeds up to 26 mph?

Quite simple, you start with the core of the body where movement originate. Although this is moving very fast linearly, the movements of the head, spine, and pelvis are actually quite small and easy to control. This belies there importance however. You see, if the core of the body is appropriately positioned (running tall, slightly posterior pelvic tilt, head in line with spine and pelvis, spine and pelvis rotating in all three planes harmonically with the limbs) the correct actions of the limbs will happen as a result.

How does one think fast enough to send a signal for the muscles to react in hundredths of a second in order to line up a landing spot for the ultimate angle, adjusting for wind conditions and surface changes?

Well no one in track I know adjusts for wind conditions or surface changes (other than elite runners who know how to run in tune with Mondo or maybe those who change their acceleration pattern do wind). I agree that it would not be advantageous to try to line up shin angle or focus on specific muscle contractions. This isn't where I'm saying technique focus should be. As I said before if you take care of the positioning of the core of the body you'll take care of most of the movements of the limbs. Also, one can quite easily send a signal to the muscle to prepare for ground contact. Ground contact is approximately 0.10 seconds long and flight time is approximately 0.13 seconds long. If you're saying that in 0.13-0.23 (a range accounting for just flight time to flight time + ground contact time) you can control the movements of your limbs I'd tell you that it's a wonder you've lived so long because humans produce volitional movements within this time frame all the time. If we didn't we'd be hit by cars for failing to move and no golfer could ever hit a ball (much less a baseball or tennis player).

How does one do this for stride after stride in rapid succession? I don't think so.

Apparently you thought wrong. You see the nice part about human movements, especially cyclic repeated ones like sprinting, is that if you get things right initially they tend to stay right. If things start bad or go sour, it becomes difficult to change them because of the reflexive nature of the activities. This isn't to say that they can't be changed….it's just much more difficult to do so. This isn't to say that technique isn't important. In fact it means that technique is VERY important because if improper mechanics are used initially it is difficult to recover due to the elastic / reflexive / involuntary nature of many of the movements that will follow.

Force plates don't lie, they don't make up numbers, they don't sell books, they don't put on seminars with snappy quotes (yes, I do sell books and I do put on seminars but I'm not a force plate  :bigsmile:) and they ignore vectors. They merely register force.

HOLY SHIZNIT!!!! You couldn't be more wrong on several levels. First, force IS A VECTOR. That means it has both magnitude and direction. What kind of force plate do you use that ignores vectors! Did you buy that at Wal-Mart? I hope it was on sale. Perhaps you can still return it if you have a receipt.

Even the most basic force platforms that only register force in 2 planes and are only used for balance tests still register a direction of force application. The best force platforms in the world (like the one's embedded in Dr. Weyand's treadmill) register the direction of the vector in all three planes (X, Y, Z). All three directions may not always be reported but they are definitely registered. I refuse to argue this point.

Although I've never worked directly with Dr. Weyand or his lab I have done research with sprinters at least as fast as those used in Dr. Weyand's research on one of the only other (I believe there are 5 in the U.S) high speed treadmills embedded with force platforms. I suggest you amend your view that force platforms do not register vectors as this is UNDEBATEABLY WRONG. Forces are vector quantities and it is impossible for a force platform to register force without regard to the direction of the force.

To be continued when I have more time….

ELITETRACK Founder

Participant
anthony on #59469

excellent, mike, as always.

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