Elitetrack: Sport Training & Conditioning

Richard_703 - 17 January 2007 06:42 AM

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.

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".

now I'll reread your post…

Richard_703 - 18 January 2007 09:19 AM

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".

now I'll reread your post…

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.

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?

Richard_703 - 18 January 2007 10:15 AM

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.

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).

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. 

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_703 - 19 January 2007 06:08 AM

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.

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.

Barry:

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

danimal9 - 19 January 2007 01:50 PM

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:

Bear - 16 January 2007 10:03 AM

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….

excellent, mike, as always.

I wanted to reinforce something from my last post….force does not HAVE a vector….FORCE IS A VECTOR! Vectors by their very nature have both magnitude and direction. We CANNOT accurately speak of force in a mechanical sense without regard to its magnitude or direction.

Despite all that, do you know anyone that can lift more than 3 times their bodyweight on one leg in .10 seconds? If you could find someone (you won't), could they do it over and over again for the number of strides in a 200m race? 100m? 50m?

This is an absurd and illogical argument that leads us nowhere. If we drop a steel ball from 10 feet in the air it will produce a force somewhere on the magnitude of 8-12x its weight. Do we question or wonder why the ball cannot �??produce�?� this force while in a stationary position. I don�??t think so. Comparing the ability to apply forces in a controlled lifting environment to the forces that are generated by a falling body at ground contact is like comparing apples to oranges.

Kinematics is defined as the branch of mechanics concerned with motion without reference to force or mass. Kinetics is defined as the branch of mechanics concerned with the forces that cause motions of bodies.

Thanks for the definitions. That was great. Now all you need to understand is that they are not independent of one another.

The preponderance of sprint training protocols are based upon kinematics with little or no kinetic basis.

This is true. I think this is because it is often easier to effect kinetics by coaching kinematics than kinetics. Coaches can easily see the kinematics that are associated with the desired kinetics. This is why we primarily coach using kinematic cues (posture, limb position) rather than kinetic cues (push harder).

Please address the following questions:
1. Does the direction of force applied to the ground matter at all?

This is another "vector" question and an over simplification of the issue. Does it matter for the runner in the sense of volitionally creating a running vector? No. The combination of the runners isometric strength to offset gravity and the braking effect at toe-down create the runners vector.

WOW. You say that I�??m oversimplifying and this is what you have to offer. As I said before FORCE IS A VECTOR. That means that it has both magnitude and direction. This is not my definition. This is physics / mechanics. In fact, it�??s very basic physics / mechanics. This is undebatable. By not recognizing the fact that you can�??t discuss force accurately without regard to its magnitude AND direction, you are showing the source of your misunderstanding.

The vertical aspect dominates the horizontal, but both are necessary for forward propulsion.

No argument here.

2. What is chemical work?

Volitional contraction by the runner, with an excessive metabolic cost. The spring-mass model describes the method that minimises metabolic cost.

In the most accurate sense, the spring mass model is what is called a simulation or behavioral model that doesn�??t really address metabolic processes at all. To make assumptions about metabolic efficiency isn�??t really the intent or the purpose of the spring-mass model and to do so would not yield perfect results. Having said that, it is true that actions that elicit the stretch-shortening cycle and take advantage of the elastic properties of the tendons are more metabolically efficient than strictly concentric actions.  I am not arguing this by any means.

3. Does the runner need to offset the effects of gravity?

Yes, it is the most critical aspect. Mass-specific force to offset the effects of gravity has a linear relationship to speed. It is so critical that changing MSF by 1/10 the runners bodyweight could increase speed by 1 meter per second. It is not a "technique". MSF is primarily isometric.

You were going good until the last sentence. I�??d argue that eccentric is a more appropriate description. There is an overwhelming amount of muscle-mechanics research which indicates that the musculo-tendonous unit lengthens prior to contracting. The lengthening is an eccentric loading that stores energy in the tendon and elicits a supramaximal contraction of the musculature (because of the stretch-reflex) to produce a concentric action that is far greater than what could be achieved without being immediately preceded by the eccentric loading.

4. What is more important to sprinting- concentric strength or eccentric strength or some other form of strength?

Concentric strength is critical at the start to overcome inertia and it is volitional. After the first few strides, pure concentric strength gives way to the spring-mass model's description of what is essenentially a bouncing ball using ground force reaction and eccentric loading that begins at ground contact. I have been diligent in looking, but so far, no one has come forward to take credit for the bouncing ball's training regime. Maybe they are too busy working on a new technique?

I�??m not quite certain what you�??re trying to say here but it sounds as if you�??re using poor logic again and comparing apples to oranges. As I said before, the spring-mass model is a behavioral model. The bouncy ball used by myself and others is a conceptual model. Both are used to further our mechanical understanding of sprinting and are by no means intended to be a complete explanation of sprinting. You seem to be taking them out of context.

5. How is "elastic force" produced?

The short version: the overwhelming force at ground contact CAUSES the runner to dorsiflex the grounded foot, creating the eccentric contraction in the posterior muscles, tendons and ligaments. Potential elastic energy is produced and stored by the limb, then released as part of the vertical impulse. Elastic energy not used dissipates as heat.

Good. We agree on something. I do want to say that I do think that the foot should be in a neutral position just prior to ground contact. I don�??t think it needs to be greatly dorsiflexed but I do think that a neutral to slightly dorsiflexed position produces several benefits such as greater negative foot speed, pre-stretch of the gastroc-soleus complex, and improved touchdown position with respect to the athlete�??s center of mass.

As for running mechanics, this is what the Weyand study states, "Although sprinting abilities differed greatly among subjects and the top speeds of the same runners differed considerably on the different inclines, the mechanical means by which runners increased speed from a jog to top speed varied little. Across each individual's speed range, speed increases were achieved primarily by increasing stride lengths at lower speeds and stride frequencies at higher ones. The more rapid increases in stride frequency as subjects approached their top speeds were achieved through reductions in both the contact and swing times that make up the total stride time…These aerial time reductions resulted from decreases in effective impulse, the product of contact time and effective force, which determines the time a runner spends in the air. Reductions in vertical impulse as top speed was approached were due to decreases in the time of foot-ground contact that were larger than the increases in the effective force applied to the ground."
In a nut shell: There was little mechanical difference between a 11.1 mps runner and a 6.2 mps runner (no mention of significantly better technique causing significantly better running mechanics by the faster runners).

Poor assumption�?�.but I�??m sure it�??s gimmicky enough to help you sell your ideas. The only kinematics Weyand and colleagues looked at were temporal and velocity related. He did not look at what most people call �??technique�?� (the positioning of body segments with respect to each other and the ground�?�joint angles, joint velocities, angular accelerations, etc) so you can�??t make conclusions on something he did not examine. Read the study again.

Longer stride lengths early in the running gave way to increased stride frequency at higher speeds. Stride frequency increased because of reduced ground contact time and swing time (reduction in ground contact time because of better mechanics? No. Perhaps Newton's law? After all, it is the collision of 2 bodies, isn't it? ). Aerial times were reduced because because effective impulse (impulse in excess of mass) decreased (no mention of changes in running mechanics? better form? better angle of arms during armswings?).

Gosh�?�this is getting absurd�?�.for goodness sake�?�did he look at changes in running mechanics (positioning of body segments with respect to each other and the ground�?�joint angles, joint velocities, angular accelerations, etc). The answer is NO. Perhaps you are unfamiliar with research practices but here�??s a crash course�?�.you can�??t draw conclusions about things you don�??t study. It would make no sense for him to comment on running mechanics when he really didn�??t do an in-depth study of kinematics.