mechanical work

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imported_hannesburk

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hey guys

the HST-Community in the german board are discussing about the speed is king-phenomenon.

it says: mechanical work = (newton) F = m*a

that means load* acceleration= mechanical work

this leads to the conclusion that 5reps with a 1/2 cadenz is superior to 5reps with 2/4 (more acceleration, same load)

but that seams very unlogical to me..the TUL is twice as big in the second example and this counts to,doesn't it?

where lies the missunderstanding?

and does more mechanical work not implicit means more p38-activity?


regards
 
First there are some inaccuracies here

1. F=M*A, The amount of Force is equal to mass multiplied by the acceleration of the object

2. W=F*D, The amount of Work is equal to the force multiplied by the distance the object is moved
 
ok that means that the distance increases along with the number of reps that would explain why more volume means more mechanical work,but what is it with the acceleration?

your definition still leads to the conclusion that 5reps with 4/2 produces less work than 5reps with 1/2 because the distance remains the same.load also, but acceleration is bigger with 1/2

help me out!!

regards
 
The tension generated by a muscle depends on the total number of cross-bridges attached. Because it takes a finite amount of time for cross-bridges to attach, as filaments slide past one another faster and faster (i.e., as the muscle shortens with increasing velocity), tension decreases due to the lower number of cross-bridges attached. Conversely, as the relative filament velocity decreases (i.e., as muscle velocity decreases), more cross-bridges have time to attach and to generate force, and thus tension increases.

Muscles are strengthened based on the force placed across the muscle. Higher forces produce greater tension. Therefore, exercises performed with muscle activated in a way that allows them to contract at high velocities, necessarily imply that they are also contracting with relatively low force. This is intuitively obvious as you lift a light load compared to a heavy load—the light load can be moved much more quickly. However, these rapid movements would have very small tension effects since the muscle forces are so low.

Looking at P38 and tension we can sumise that the slower contractions induced by heavy loading allow greater tension to be acheived and for a greater amount of time. Greater tension has been shown to illecit the P38 response.

I hope that makes sense. It did in my head anyway ;). That only covers active tension properties, passive tension must also be taken into account since we are dealing with the whole tissue, which if need be I'll explain later.
 
[b said:
Quote[/b] ]your definition still leads to the conclusion that 5reps with 4/2 produces less work than 5reps with 1/2 because the distance remains the same.load also, but acceleration is bigger with 1/2
Click to expand...

It's not my definition, this is Newtons 2nd Law. Lets' view it this way. You're holding a weight of 20 Lbs. As fast as you can, you curl it, in let's say 1 Sec. Now if you increase that Mass (Weight) by twice or 40 Lbs do you think you can still curl in 1 sec. The answer is NO it takes longer. So the speed at which you move the weight is directly proportionate to the mass. This is called the Force Velocity curve, the higher the external force the slower you can move it, take that with what I said in the preceding post about tension development because of crossbridge binding and you have your answer.
 
@dkm thx a lot, but I am still confused,more than before...

I still do not know if Tension is higher with a faster cadence or with a slower.
what I think you said is that tension is lower if velocity and so acceleration is higher because there is little time for cross-bridges to attach, that would mean the opposite to Newtons law.

But I also see that you say that higher Load leads to slower cadence because velocity is direct proportional to load.

from my experience this is definately right but as I workout during the 15s my cadence is usually very slow because I can handle slow reps and a high TUL,when I reach the 5s the velocity of my reps increase because weight is so heavy that I can no longer move it very slowly

that would be just the opposite of what you said.

I am really confused. is now 5reps with 1/2 better for p38-activity than 5reps with 2/4 with the same load, or not?

sorry for my missunterstanding but this is kind of complex

In the german boards everyone says that just the newton Law counts and that in addition 1/2 leads to 2times as much tension as 2/4 for a given number of reps and a given load
can this be correct ? I think not!

regards
 
Let's keep it simple.

Tension is a matter of weight. The heavier it is the higher the tension. The more tension the better for P38. Physiology tells us (force velocity curve) that the heavier it is the slower we can move it.

So except in the first few reps we really can't increase the speed at which we move the weight.

[b said:
Quote[/b] ]But I also see that you say that higher Load leads to slower cadence because velocity is direct proportional to load.

from my experience this is definately right but as I workout during the 15s my cadence is usually very slow because I can handle slow reps and a high TUL,when I reach the 5s the velocity of my reps increase because weight is so heavy that I can no longer move it very slowly
Click to expand...

Now think about this, during the 15's you choose to move the weight slower but in all actuallity you can move it a whole lot faster.

I also think you are confusing concentric contraction and what happens during an eccentric contraction. Let's concentrate strictly on concentric.

During your 15's you can concentrically curl 10lbs a whole lot faster than 50 right.

Now do you see what I am getting at?
 
I think I see what you mean. I understand that there is little room for increase velocity when using heavy weights.

but when I get you right I would be fine using a much quicker cadence during 15 because then I would be able to increase velocity and because newtons 2 Law still counts I would be able to reach higher tension with the same number of reps...

light loads and slow cadence is worst for p38 ,right?

but am I also right assuming that it is not quite true that 1/2 leads to twice as much tension as 2/4?
a 1second concentric phase would lead to twice as much tension as a 2 second concentric phase (with the same weight) but excentric can not be rated with the Newton Law, because they have also other impacts on p38 (first of all the stretch)

I just want to know how good the Newton Law can really be applied for the tension-thing

you are great
worship.gif


regards
 
[b said:
Quote[/b] (hannesburk @ Mar. 08 2005,11:19)]I just want to know how good the Newton Law can really be applied for the tension-thing
you are great  
worship.gif

regards
Click to expand...
It really is hard to apply Newtons law's (2 and or 3) to muscle and tension. It is easier to use 2 different ideas, the Length Tension Relationship and the Force Velocity Relationship.

Length Tension is simply stating that at any given length the muscle produces a tension and at differing lengths this changes. Why it changes, because there are optimal lengths were the most crossbridges bind.

Force Velocity is simply stating that the lower the force the faster you can move it.

Let's use this analagy to look at both.

There is a truck attached to a rope, on the other end is 10 guys pulling on the rope or 20 hands on the rope, when all 20 hands are on the rope and pulling the highest tension is observed, with me so far?

Now if the truck starts backing up and the 10 guys have to continually take there hands off to reposition and pull then tension is reduced because not all twenty hands are pulling at the same time(Thanks Ron ;) ). Got it?

This pretty much kinda represents cross bridge action, the more crossbridges attached the greater the tension.
 
I'll also add that many of the studies with force-velocity curves were a product of isokinetic measuring devices. What that means is that, for a given velocity, it applies 100% force. Or to put it another way, if you were lifting something really heavy, of course the weight will move really slow. And when you're lowering the weight, the weight moves really fast.

For some reason, a whole bunch of guys (even Mel Siff, I think) misinterpreted these studies and suddenly people are trying to correlating force-velocity curves with actual active tension. The Morgan and post-Morgan studies show, again and again, there isn't a correlation between force-velocity and tension as long as the movement is discernably eccentric vs. static vs. concentric in order to facilitate different phenomena with crossbridges.

Again, explosive training is a different beast. There, you're adding the myotatic reflex and -- boom -- instant force impulse, that significantly elevates active tension for about 30% of the total movement.

cheers,
Jules
 
[b said:
Quote[/b] (hannesburk @ Mar. 08 2005,5:32)]In the german boards everyone says that just the newton Law counts and that in addition 1/2 leads to 2times as much tension as 2/4 for a given number of reps and a given load
can this be correct ? I think not!
regards
Click to expand...
No, not in all boards and not everyone. Keep distance from generalizations.
 
@Hypertrophier: you are right! but even the most knowledgeable mods do at bbszene.de..
 
[b said:
Quote[/b] ]Again, explosive training is a different beast. There, you're adding the myotatic reflex and -- boom -- instant force impulse, that significantly elevates active tension for about 30% of the total movement.
Click to expand...

Vicious, what can you explain about explosive training vs. regular speed reps and their affects on hypertrophy?

The quote you stated above sounds positive about explosive (or faster rep) training.
 
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