Is Average Force the Same in Fast vs. Slow Weightlifting Reps?

[sophiecentaur]

Wayne. I think I have spotted your problem. It's an emotional one. You find it hard to accept that lifting weights is totally inefficient, albeit good fun and making muscles big. That's all there is to it.
If you really want your exercise to be useful then hook yourself up to a generator. ;-)

 

[waynexk8]

Technically the meaning of work is:
W=\int \mathbf{F} \cdot \mathbf{dx}
if the force is constant then that simplifies to
W=\mathbf{F} \cdot \mathbf{d}= F d \, cos(\theta)

The cosine term is very important. When the angle between the force and the displacement is 0º (as in when you are lifting the weight) then the cosine evaluates to 1 and the work is positive, but when the angle between the force and the displacement is 180º (as in when you are lowering the weight) then the cosine evaluates to -1 and the work is negative. Thus during concentric contractions the muscles do work on the weight and during eccentric contractions the weight does work on the muscles.

Hmm, So as I am lifting the weight and using force and energy, and sort of putting energy as in movement into the weight that’s doing work ? If am right there, as I am using force to slow the weight down on the eccentric contraction, am I not also using force and thus putting energy in the weight when lowering it, as I am reducing its natural speed, its fall to the floor ?

Sure, but work is different from force. You are exerting force, that does not imply that you are doing work.

Right get that, if its not moving I could be producing force but not doing work.

You can't have it both ways. If the work does work on you then you do not do work on the weight. Your statement here is a self-contradiction.

Not sure about that and if its contradictory, let me explain, as it can be both ways.

As I am lowering the weight under control, thus using force and energy when the weight is moving thought a distance, and also the weight is doing work on me, as its pushing down on me with a force its weight due to gravity, and the weight is again moving thought a distance, so the weight is pushing down and I am pushing up whilst the weight is moving.

Wayne

 

[JaredJames]

Hmm, So as I am lifting the weight and using force and energy, and sort of putting energy as in movement into the weight that’s doing work ? If am right there, as I am using force to slow the weight down on the eccentric contraction, am I not also using force and thus putting energy in the weight when lowering it, as I am reducing its natural speed, its fall to the floor ?

Read my example.

The fact the weight is descending indicates the force downwards is greater and as such the work done is by the weight on your arm.

Not sure about that and if its contradictory, let me explain, as it can be both ways.

As I am lowering the weight under control, thus using force and energy when the weight is moving thought a distance, and also the weight is doing work on me, as its pushing down on me with a force its weight due to gravity, and the weight is again moving thought a distance, so the weight is pushing down and I am pushing up whilst the weight is moving.

Wayne

You certainly are contradicting yourself.

Once again, you are ignoring the fact force has a direction and that 10N upwards cancels out 10N downwards.

Put extremely simply:

Let's say the weight is 10N. That is 10N of force acting continuously downwards.

So, to raise the weight 1m, you apply 15N of force upwards. This gives you 10N from the weight downwards plus 15N of force upwards. 10N down + 15N up = 5N up. So, work done = 5N upwards x 1m = 5J of work done up.

Now, to lower the weight 1m, you apply 5N upwards to slow its descent. This gives you 10N from the weight downwards plus 5N of force (from you) upwards. 10N down + 5N up = 5N down. So work done = 5N downwards x 1m = 5J of work done down.

So you now have total work done = 5J up + 5J down = 0J.

Your total work done is zero. However, you have expended 10J of energy to apply the required forces.

Do you understand now?

LEARN THE MEANINGS OF THE WORDS AND USE THEM PROPERLY

 

[waynexk8]

OK, let's look at this. You agree that the work done on the weight over one rep is 0. So if I do one rep in 10 s then that is 0 J work done. On the other hand if I do 3 reps in 10 s then that is 0 J + 0 J + 0 J = 0 J work done. So the work done is 0 J in both cases and therefore since 0 J = 0 J the work done is the same in both cases.

Again, your statements are self-contradictory. If the work done over one rep is 0 then logically the work done is the same for fast and slow reps. You cannot say "yes" to 2) and "no" to 2a) without contradicting yourself.

I do not think the meaning of work, that is if you move a weight up and then down = zero, is helping this debate at all. As we all know here that force and energy have been used to lift the weight and to lower it under control, thus physical work has been done. Therefore, it seems no one can work out the force used, but whatever the force the average force is the same.

However if we take some numbers, and as numbers are pretty close, as of the study and tests I remember looking at, we find that what I said before. And as we all know that the energy is far far far higher in the faster reps, I ask again, why do you think this is ?
Fast reps,
140, 100, 100, 40, 20.

Slow reps,
80, 80, 80, 80, 80.

I say its because the overall or total force thus tensions on the muscles are higher. As with the faster rep I have more power, coved more distance, used more energy, and used a higher force more times. And it’s these higher high forces, and the higher peak force, and as there are more of these in the same time frame “WILL” put more tension on the muscles, that’s why the muscles use more energy, because they are putting out more higher high force and the high peak force, and the slow reps medium forces cannot make up for this when the fast reps forces are using low forces on the decelerating for the transition.

It would be the same if there fast reps were 3 reps done at 3/3 = 18 seconds, and the slow reps were 1 rep done at 9/9 = 18 seconds. The higher high forces and the higher peck forces would have to be higher in the faster 3/3 reps, but just not as much as in a .5/.5 set of reps.




Or if anyone does not agree with that, then why do they think I use more energy in the faster reps ?

Wayne

 

[waynexk8]

Dammit wayne stop this non-sense. Either learn what these words mean or just drop it.

What part of force has a direction are you not understanding?

As you clearly aren't prepared to learn these things, you're just going to have to accept the following:

If the weight gives a downwards force of 10N and you provide an upwards force of 5N (to stop it freefalling), the net force is 5N downwards and that is the force you use to calculate the work done. The work done is in the downward direction - or more correctly, it is done by the weight on you. You have expended energy to generate the counteracting force, but you haven't done any work. Period. End of story. Finito. Drop it.

Ok so your saying even thou I have used force and energy to lower the weight under control, because it’s in the negative direction I can/have not done work on it, if that is right I get what you mean about me not doing work.

Wayne

 

[JaredJames]

why do they think I use more energy in the faster reps ?

In the fast reps, the work done may still equal zero, but you've still expended the energy to move the weight X times more than in the slow ones (as per above you can add up the energy use to give the total expended).

It's as simple as that for why you use more energy.

 

[Dale]

Hmm, So as I am lifting the weight and using force and energy, and sort of putting energy as in movement into the weight that’s doing work ? If am right there, as I am using force to slow the weight down on the eccentric contraction, am I not also using force and thus putting energy in the weight when lowering it, as I am reducing its natural speed, its fall to the floor ?

No, reducing its "natural speed" does not imply that you are doing work. In fact, most useful means of extracting work from gravitational potential energy involve exactly that. Think of hydroelectric power, a turbine or even a watermill slows the decent of the water, and yet the water does work on the machine, not the other way around.

Going back to the definition of work, you can see this for yourself:
a) determine the direction of the force (upwards)
b) determine the direction of the displacement (downwards)
c) determine the angle between them (180º)
d) determine the cosine of that angle (-1)
e) if it is positive then it is doing work
f) if it is negative then work is being done on it

Not sure about that and if its contradictory, let me explain, as it can be both ways.

No, it cannot. Stop explaining and start learning.

Again, go back to the definition. If you are exerting a force on the weight then by Newton's 3rd law the weight is exerting an equal and opposite force on you. That means that if one force is parallel to the displacement then by Newton's 3rd law the other must be anti-parallel. Therefore, one force will do positive work and the other force will do negative work (i.e. work will be done on it). They cannot possibly both do positive work.

Please do not continue to reassert the same mistakes. If you do not understand then ask questions. Do not make erroneous assertions, particularly after having been repeatedly corrected.

 

[waynexk8]

Wayne. I think I have spotted your problem. It's an emotional one. You find it hard to accept that lifting weights is totally inefficient, albeit good fun and making muscles big. That's all there is to it.
If you really want your exercise to be useful then hook yourself up to a generator. ;-)

Yes lifting weights is totally inefficient.

Please don’t be like that, I am not the loud Bodybuilding type, I am a very quiet person and don’t watch Bodybuilding at all, I just like strength training for many reasons. And I know it’s hard for you explaining things to me, but I am learning and your helping me.

Wayne

 

[waynexk8]

In the fast reps, the work done may still equal zero, but you've still expended the energy to move the weight X times more than in the slow ones (as per above you can add up the energy use to give the total expended).

It's as simple as that for why you use more energy.

Yes that's what I sort of said to D. in the fiorst place, distance is important, he said it was not.

Yes but you still did not sort of answer the question, as it take “MORE” of not just energy to move the weight more times and more distance in the same time frame with the faster reps, as the energy/calories must power something, and that a force to move the muscles, so is it not like I just said above ? Here it is again; just not the percentages are higher with the faster reps.

However if we take some numbers, and as numbers are pretty close, as of the study and tests I remember looking at, we find that what I said before. And as we all know that the energy is far far far higher in the faster reps, I ask again, why do you think this is ?

Fast reps,
140, 100, 100, 40, 20.

Slow reps,
80, 80, 80, 80, 80.

I say its because the overall or total force thus tensions on the muscles are higher. As with the faster rep I have more power, coved more distance, used more energy, and used a higher force more times. And it’s these higher high forces, and the higher peak force, and as there are more of these in the same time frame “WILL” put more tension on the muscles, that’s why the muscles use more energy, because they are putting out more higher high force and the high peak force, and the slow reps medium forces cannot make up for this when the fast reps forces are using low forces on the decelerating for the transition.

It would be the same if there fast reps were 3 reps done at 3/3 = 18 seconds, and the slow reps were 1 rep done at 9/9 = 18 seconds. The higher high forces and the higher peck forces would have to be higher in the faster 3/3 reps, but just not as much as in a .5/.5 set of reps.


Wayne

 

[waynexk8]

No, reducing its "natural speed" does not imply that you are doing work. In fact, most useful means of extracting work from gravitational potential energy involve exactly that. Think of hydroelectric power, a turbine or even a watermill slows the decent of the water, and yet the water does work on the machine, not the other way around.

Going back to the definition of work, you can see this for yourself:
a) determine the direction of the force (upwards)
b) determine the direction of the displacement (downwards)
c) determine the angle between them (180º)
d) determine the cosine of that angle (-1)
e) if it is positive then it is doing work
f) if it is negative then work is being done on it

No, it cannot. Stop explaining and start learning.

I will have to come back to that one, as its very late here.

Bye for now all.

Wayne

 

[Dale]

I do not think the meaning of work, that is if you move a weight up and then down = zero, is helping this debate at all. As we all know here that force and energy have been used to lift the weight and to lower it under control, thus physical work has been done.

I have told you this many times already. Energy has been expended, but no work has been done. What is not helpful for the debate is for you to use the incorrect terminology when the correct terminology has been provided. These are technical words with specific mathematical meanings. If you want to learn science, which you have claimed several times is your goal, then you need to learn the meanings of the terms and use them correctly.

 

[JaredJames]

thats what I sort of said

so is it not like I just said above

However if we take some numbers,

I say

It would be the same

Stop all of this and start learning.

1. What you say contradicts itself.
2. As point 1.
3. Your numbers are meaningless.
4. You keep trying to explain things using incorrect knowledge.
5. A conclusion based on the above incorrect knowledge.

You need to try and understand this. How many times have you posted those numbers and how many times has everyone ignored - every time.

You are ignoring what you are being told and trying to apply your own flawed explanations. Just stop it.

 

[ZapperZ]

This thread is going nowhere fast. It is now done.

Zz.