# Tension or is it to hard to work out with physics ?

tension or is it to hard to work out with physics ???

Hi there, I have posted somthing the same, however new evedence has come up.

Some say the force thus tension on the muscles has the same average, lets just say for now the force thus tensions are the same. We are using say the bench press, and useing 80% of a persons rep. max. }so the persons max. strength/force = 100 pounds} call it 80 pounds moving the weight 1m up and 1m down, on 1 rep at 3/3{3 seconds up and 3 seconds down} = 6 seconds and 6 reps at .5/.5 {half a second up and half a second down = 6 seconds and/or 4 reps at 3/3 = 24 seconds and 24 reps at .5/.5 = 24 seconds.

Now I thought of a crude test, a clay test, you put a peace of clay between your hand and the weight, and 99.9 of the people would say that after you did the rep/s you would flatten out the clay far far far more with the faster reps, as of the higher peak forces, higher high forces and speed.

Shall we say these are the rough forces per one fifth of each rep, and I will leave out the peak forces for now. And as you knowe the faster rep will need a longer time to deccelerate for the change in direction from posative to negative reps.

Fast rep,
100, 100, 100, 80, 20.

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

HOWEVER, some say as both reps have an average force, the overall force thus tension in the end will average out and be the same, but my problem is I think diffrent, as why does not the both reps average out the flattening of the clay in the end !!! If you see my point, as the faster reps will flatten the clay much more than the slow reps, thus there is more force/tension with the fast rep/s. As you know all to well the faster reps have much more of a power {work energy} in them.

Wayne

AlephZero
Homework Helper

Make some assumptions and see what the numbers say. You are moving with peak to peak amplitude of 1m, in either 6 sec (3 up 3 down) or 1 sec (0.5 up 0.5 down).

Assume the weight is doing simple harmonic motion up and down. That is probably not a very good approximation but it's easy to calculate

Amplitude = 0.5m, frequency = 0.167 Hz or 1 Hz.

Maximum acceleration = a times (2 pi f)^2
= 0.55 m/s or 19.7 m/s
So the maximum force would be 1.06 times the weight lifted for the slow case, and 3 times for the fast case.

Don't take those numbers as "accurate" but they do suggest there would be an effect.

The lifter might apply a large force for a short time and then ease off, rather than a smaller force for the whole 3 seconds. That would reduce the difference in the peak force.

Both reps only have the same average force if you average the up and down forces together. The average force up will be higher for faster reps and the average force down will be lower. (That statement includes some more hidden assumptions about how the lift is done, but the basic idea is probably correct).

Make some assumptions and see what the numbers say. You are moving with peak to peak amplitude of 1m, in either 6 sec (3 up 3 down) or 1 sec (0.5 up 0.5 down).

Assume the weight is doing simple harmonic motion up and down. That is probably not a very good approximation but it's easy to calculate.

This is very good, as your right, we do not need numbers down to the Atom, just close approximation.

Amplitude = 0.5m, frequency = 0.167 Hz or 1 Hz.

Maximum acceleration = a times (2 pi f)^2
= 0.55 m/s or 19.7 m/s
So the maximum force would be 1.06 times the weight lifted for the slow case, and 3 times for the fast case.

Don't take those numbers as "accurate" but they do suggest there would be an effect.

My physics is not half as good as you, but am trying to learn, so if what I say is wrong please stay with me.

Are you saying that the total, or overall force thus tension on the muscles will be 1.06 with the 1 slow rep, and 3.18 with the 6 fast reps ??? As this is what I was thinking, that the peak highs and the highs in the fast rep, and the slow reps lower forces even thou they are more constant can not make up.

The lifter might apply a large force for a short time and then ease off, rather than a smaller force for the whole 3 seconds. That would reduce the difference in the peak force.

Yes thats more what I was thinking, as we have the fast rep as I said,

First Fast rep,
100, 100, 100, 80, 20.

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

However then we have the second fast rep, and as its being moved down 1m at .5 of a second its going to put more force/tension on the muscles to stop the moving down soping and moving it up. but no need to get into this.

Both reps only have the same average force if you average the up and down forces together. The average force up will be higher for faster reps and the average force down will be lower. (That statement includes some more hidden assumptions about how the lift is done, but the basic idea is probably correct).

Wayne

Last edited:

Both reps only have the same average force if you average the up and down forces together. The average force up will be higher for faster reps and the average force down will be lower. (That statement includes some more hidden assumptions about how the lift is done, but the basic idea is probably correct).

Ha, so the forces will be higher going up, and I imagine far higher going up in the second rep as I explainded above.

To be honest we are not to concerned with the going down or eccentric, as problems come in here. Hope I explain this right. As in the eccentric the muscles are 40% stronger, so basicaly in all lifting the eccentic portion of the rep the muscles are underloaded. so even if the slow rep could make up on some force/tension, it would not relly mean anything as I said the eccentric is very underloaded.

Wayne

Hi there,

To be honest this debate is going on with quite a large number, and for quite some time, however I/we needed an independent view.

One of the people debating we me, has asked me to give you the below. I will say in my laymans terms, hold on no need for that, I can give you my video of both the reps,

Here is what my frend told me to show you, as he says the average forces are the same in both the concentric and eccentric.

Just tell him:"a friend of mine says that for both the up and down motion the starting and ending speed is zero since the weight changes direction.So the average acceleration is zero since a=(V2-V1)/t=(0-0)/t=0 and so the average force(F=mg+ma) is equal with the weight(F=mg) for both the up and down motion."

Tell him that and he'll understand.

Wayne

However I have another problem/question here if the average force is the same. Let us say that if force is = to tension, and in this example they are, thus there is more tension to the muscles in 6 reps at .5/.5 = 6 seconds to 1 rep at .5/.5 = 1 second, thus there must be more/longer force if there is more longer tension.

So if you agree that the forces are the same, is there either the same tension in 1 rep at .5/.5 and 1 rep at 3/3. Or there is the same tension in 6 reps at .5/.5 and 1 rep at 3/3. As there is and can not be the same tension to the muscles in 1 rep at .5/.5 and 6 reps at .5/.5 if you see my point.

Wayne

Sorry, I did not explain the clay test fully, clay test, you put a piece of clay between your hand and the weight, and then use 80% of your RM or 80 pounds, and first do 6 reps at .5/.5 = 6 seconds with one hand, and then do 1 rep at 3/3 = 6 seconds. Now if as some “think” that the average force will all equal out in the end, the clay should flatten to the same in each rep, but it does not, it’s far far far more flattened with the faster reps.

This must be because there is more overall/total force/tension on the muscles.

As we all agree that we are using more Power {work energy} in the faster reps, and more work means more energy transferred by a or more force acting through a distance ???

Wayne