Hmmm, I see no connection to what I wrote. 
A spring can work in more than one direction. As we near mosquito season I am counting on my screen door to close! Muscles work in both directions. Granted, the amplitude may differ between ecc & conc. but isnt there force present in both? voluntary or involuntary? lengthening and shortening?
Yes a spring can work in one direction. Yes, you can count on your screen door to close. Yes, muscles work in both directions. Yes, amplitude may differ between ecc and conc. Yes, there is force present in both. Yes, something is voluntary or involuntary. Yes, shortening and lengthening occurs. Yes, the spring mass-model is based on the impulse that occurs from muscles rapidly lengthening then immediately shortening after the falling body contacts the ground and creates ground reaction force. Yes, this is not a matter of debate, it’s what actually happens regardless of whether or not your screendoor lives up to your expectations.
Again, I apologize for my use of the term absorb. Perhaps I should say store? In either case, I use depth “landings” to train an athlete to become better at stabilizing and absorb/storage. For me to take them to depth drop with rebounds, I am looking for improvements in stabilizing & absorption to a point where the involuntary concentrics start to occur in free form (non-instructed) This to me relates directly with the power curve.
I think that whatever it is you’re saying must have some merit for you to say it so eloquently. It’s especially exciting that there is a connection, a bonding so to speak, with the power curve. I think that what you ultimately will accomplish is a non-instructed, free form involuntary concentric contraction that would most likely have occured regardless of the non-instruction instruction that preceeded it.
Running/jumping is an elastic activity. When foot strike occurs, the force on the Earth is the same as Earth’s force on the foot. However, due to the athlete being of far less mass than the earth, Newton’s second law predicts that the athlete’s acceleration will be much greater.
Greater force brought to bear = greater potential Ground Reaction Forces.
If you are going to ding me on my use of the term absorb, then I question the use of the word reaction when used in GRF.
Reaction syn: respond, result. Response to what? or Result of what? Previous application of force to the ground that occured when?
F=ma. In running, the body elevates against the force of gravity, then falls. The mass of the body accelerates down. Acceleration of the mass = force. At touchdown, the force created by the the body striking is returned in equal measure by the earth. This force as been measured by ground force reaction plates; it is not specutlation. At this point, touchdown, the creation and storage of elastic energy occurs when the ground reaction force strikes the foot. Stored energy is released as the COM passes over the grounded foot. In addition to the ground reaction force pushing against the grounded foot, the release of elastic energy is realized, in an upward direction, putting the runner back into the air to repeat the cycle. This cycle can’t occur endlessly because the elastic response ultimately weakens to the point where creation, storage and release are no longer viable in maintaing the cycle.
Maybe I am not understanding you here. At least some of the disconnect may come from your being tethered to the Weyland study. A study realying on work from a treadmill and then assigning the attributes of a spring 1:1 to the sprinting action, does not work for me in a real-world application sense.
I can see how that could be. Those tethered to old, unproven and misapplied coaching theories always believe that things that are proven and correctly applied don’t work for them. I know I did, for awhile anyway. I think. The rest is kind of a typical strawman argument. The way to remove your tether is explain how measured forces can be so much higher and faster than what could be produce by chemical muscle mechanical work from any human being, or any animal for that matter.
In the athletic arena, there are so many variables that dont fit the consistancy / harmonics of a spring. This also may be where you and I differ on the idea of isometric contribution to sprinting/jumping. Stabilization to my view, is huge in optimal force application and return, decreased switching/reduced contact times, etc, in real world / real time applications.
I’m sorry, but your argument is not with me, it is with every locomotion expert. The concept of the spring-mass model as an explanation of measured forces, measured metabolic costs, etc, had its beginnings dating from 1964, and has had ample research from the 1970’s to the present. Only coaches, whose expertise is not in science, and even less in research methods (i.e., the “problems with treadmill testing are blah blah blah”) refuse to accept the results and the concept.
The bottom line is simple, from Parmenides: what is is. Doesn’t matter whether or not we like it, hate it, accept or deny it.
“Training, or lack thereof, has nothing to do with eccentric contractions in sprinting.”
Not sure where to even begin with this one so I will defer…
5th IOC World Congress on Sport Sciences
with the Annual Conference of Science and Medicine in Sport 1999
Sydney 31 October -5 November 1999
No need to defer! Your statement and question:
"[i] How about “Eccentric RFD cannot dictate GRF because the force is in the opposite direction” Not being full vested in Dr Weyland’s work, would you tell what it is that determines the quality/nature of the GRF?
Were we talking about an un or undertrained person, that would be one thing, but I dont accept your discounting of the eccentric contraction. [/quote][/i]
Elicited my response. I did not discount eccentric contractions. I said they cannot dictate GRF. Much of what your saying in this discussion follows this same line. You make connections where they don’t exist and break them when they do exist.
It would be extremely difficult to run without eccentric contractions. GRF is caused by something striking the ground. Eccentric contractions of the posterior chain are CAUSED when striking the ground, they do not cause ground reaction force, accelerating body mass does. The cause of both GRF and elastic reponse is the falling body striking the ground.
