Can you push down more than your weight?

[jacebargo]

quick question...is it possible to press down more than you weigh without being strapped in ?

 

[Doc Al]

quick question...is it possible to press down more than you weigh without being strapped in ?

I don't see how, not without accelerating. You, of course, could jump in the air and hit the floor with a force greater than your weight, but I assume that's not what you are talking about. Pressing down on a bar (attached to a pulley and weights, say) smoothly and continuously, the best you can do is lean all your weight on it.

 

[jacebargo]

im talking about in a seated tricept machine. with a cable and pullies. if you are seated there and without the strap around your waist. let's say you weigh 200lbs and you have 275lbs selected on the machine...can you press 275lb down when you weigh 200 without leaving the ground...thanks for your help on this

 

[Hootenanny]

im talking about in a seated tricept machine. with a cable and pullies. if you are seated there and without the strap around your waist. let's say you weigh 200lbs and you have 275lbs selected on the machine...can you press 275lb down when you weigh 200 without leaving the ground...thanks for your help on this

No, not in smooth controlled movements unless you are strapped in.

 

[jacebargo]

thanks for your help on this

 

[Doc Al]

(I think I'll move this little sidebar to its own thread, lest it confuse the original topic.)

 

[jacebargo]

Well, I don't know what I can say. What I do know is I was not strapped in and I selected 270 pounds and was able to press it.

 

[Hootenanny]

Well, I don't know what I can say. What I do know is I was not strapped in and I selected 270 pounds and was able to press it.

In smooth controlled movements, or fast explosive presses? Without wrapping your legs around anything, or pushing yourself back into the seat?

P.S. You've got your own thread now

 

[turbo]

Well, I don't know what I can say. What I do know is I was not strapped in and I selected 270 pounds and was able to press it.

You have not described the machine adequately, but if you are pressing a bar attached to a cable, and that cable loops around a pulley at the top of the weight stack, you are actually pressing 135# (disregarding mechanical drag).

 

[jacebargo]

I did smooth controlled movements. As a matter of fact, I did negative presses on the upswing. So, it was very controlled. the seat in which I sat is not straight back. It is at a slight forward angle so my body is in a slightly forward position. My feet flat on the ground and not wrapped on anything and I was not strapped into the seat.

 

[Hootenanny]

I did smooth controlled movements. As a matter of fact, I did negative presses on the upswing. So, it was very controlled. the seat in which I sat is not straight back. It is at a slight forward angle so my body is in a slightly forward position. My feet flat on the ground and not wrapped on anything and I was not strapped into the seat.

Okay, fair enough. However, as turbo said the configuration of the pulleys can reduce the amount of force required to lift the nominal mass.

 

[jacebargo]

thanks...so there is now way to push down more than you weigh, with smoth controlled movements without leaving the ground?

 

[Hootenanny]

thanks...so there is now way to push down more than you weigh, with smoth controlled movements without leaving the ground?

Not without restraining yourself with a strap or bar, no. That is why Lat Pull-down machines have knee bars, since your lats are stronger than your triceps, you can lift/pull a lot more weight with them, many times your bodyweight. Placing your legs under the bars stops you coming flying out of your seat when you pull ala chin ups.

 

[jacebargo]

thanks ...you guys are awesome

 

[Hootenanny]

thanks ...you guys are awesome

My Pleasure

 

[Joey D.]

I'm the guy doing the seated Tricep Pushdowns

Although my friend Jace positioned my original questions, we had a healthy disput this morning about this aspect of working out specifically with seated Tricep Pushdowns. I simply stated that I was able to select 270 lbs. on the machine. His response was you would be lifted from the seat. True enough if my back were not pushing in a seat at approximately 75 degrees. Additionally, my hands are grippping and situated to each of my sides. Granted there is a pully system but it behooves me to believe that 270 pounds would be reduced to approximately 135 lbs. I weight approximately 197 lbs. at 6 feet tall. Please advise.

 

[turbo]

Look at the configuration of the pulley system. In general with weight machines, if there are only fixed pulleys, their function is to change the direction of the applied force and there is no mechanical advantage. If there is a pulley on top of the weight stack and the cable wraps around that, and that pulley rides up and down with the weights, you can safely assume that it is cutting the force required to lift the weights by 50% (disregarding friction, etc), so no matter how much weight you select, you could balance that weight by putting half that amount of weights on the bar. If you've got some free-weights in that gym, you can prove it for yourself by attaching plates to the bar.

 

[jacebargo]

ok let's say the pully is just changing the direction of the applied force, and there is no mechanical advantage with the pullies...would you now have to consider the leverage. where your hands grip to where the cable is attached?

 

[Doc Al]

ok let's say the pully is just changing the direction of the applied force, and there is no mechanical advantage with the pullies...would you now have to consider the leverage. where your hands grip to where the cable is attached?

Clearly how you grip the bar will determine how much force you can apply--but never more than your weight, unless something else besides gravity is holding you down.

 

[DyslexicHobo]

You can lift more weight than you weigh, but only with some sort of mechanical advantage. These things include lever arms, screws, and pullies. If this machine uses any of these (most likely pulleys), then you can lift more weight than you weigh. This is slightly decieving, however, because if you're using a 1-pulley system to lift 270 lbs, then you only need to apply 135 lbs of force to begin accelerating the weight upwards.

You could, with frictionless pullies and a lot of massless string, lift millions of pounds with a pinky finger. This would require an extremely large distance traveled by your pinky finger for a small amount of distance moved by the weights.

This is due to the fact that the amount of work done by your hands is equal to the amount of work done on the weights. If W = Fd(cosx), and if you're applying 135 lbs of force to the bars, then you can plug into find that the weights should move exactly 1/2 the distance which your hands moved.

 

[Hootenanny]

You can lift as much weight as your body can sustain, however you can't push down with a force greater than your bodyweight with some restraining force.

 

[jacebargo]

that makes perfect sense...but what about when your pressing weight down? towards the earth. can you press down more than you weigh without holding yourself down in some way...that was the original question

 

[Hootenanny]

that makes perfect sense...but what about when your pressing weight down? towards the earth. can you press down more than you weigh without holding yourself down in some way...that was the original question

Simple answer: NO.

 

[Joey D.]

All interesting responses and thoughts. No question in my mind that all of what you state is correct. However, my only statement was that based on how you sit in this machine and the fact that your back is pushed into the seat rest... to a degree you are restrained and therefore selecting 270 pounds is not far fetched. Agreed that the system of pully's allows you to use 135 pounds of force but you would agree that 270 pounds on the machine is just that... the amount of force exerted is really the question... agreed?

 

[Doc Al]

Agreed that the system of pully's allows you to use 135 pounds of force but you would agree that 270 pounds on the machine is just that... the amount of force exerted is really the question... agreed?

If the weight stack is marked "270 lbs", then I hope the actual force required is close to 270 lbs. (That the machine would be labeled 270, yet only require 135 due to mechanical advantage, seems unlikely. Note that depending on how the machine is designed, the leverage--and required force--may change as a function of how far the cable is pulled. Some machines give a range of weight, from lowest to highest.)

The real deal would be to actually measure the force required to press down the bar using a spring scale. Or you could just tie free weights to the bar until it comes down.

 

[Joey D.]

Thank you. What you say makes very good sense and puts closure on my questions. I have learned a great deal today... tomorrow a new day and more questions... Regards...

 

[DyslexicHobo]

If the weight stack is marked "270 lbs", then I hope the actual force required is close to 270 lbs. (That the machine would be labeled 270, yet only require 135 due to mechanical advantage, seems unlikely.

Actually, in my school gym there are two tricep presses. One has a pulley, and the other doesn't. Everyone in the gym is perplexed by how they can do 120 lbs on one machine, but only 60 on the other.

 

[jacebargo]

thats cause the pulleys give you a mechanical advantage...now i feel smarter

 

[Doc Al]

Next time I'm in the gym I will examine how the machines are put together.

 

[Hootenanny]

Next time I'm in the gym I will examine how the machines are put together.

:rofl:
[color="#black"]not enough words[/COLOR]

 

[Doc Al]

Hey now... :grumpy:

 

[Hootenanny]

Hey now... :grumpy:

I never said you didn't go to the gym, I'm just giggling at the thought of you stood there explaining what your doing to the other people in the gym.

"Now assuming that both the strings and pulleys are massless ...":rofl:

 

[Doc Al]

Field report from the gym

OK, so I did check out several machines at the gym at work. The gym is small, with only two machines that could function as a triceps pressdown machine (they do not have a machine dedicated to that function). Both were Cybex machines: A cable cross-over machine and a lat pulldown machines. So this is hardly representative of all machines.

Nonetheless, for the record, both machines use a simple pulley arrangement: no mechanical advantage. Both machines use a pin to select the number of plates you lift.

The plates on the crossover machine are just labeled by numbers in sequence, not anything that is obviously the weight. The numbers do not corresponding to 10 lb increments (as one might at first think); I checked by hanging an Ivanko 25-lb plate from the cable--it could easily raise the stack at position #4.

The lat pulldown machine looked obviously labeled in pounds: 12.5, 25, 37.5, etc. I hung that 25-lb plate from the cable--it was not enough to balance weight of the 25 lb stack. Only when I hung 27.5 lbs from the machine did it balance. So, at least for this particular setting, you'd have to exert more than 25 lbs of force to lift the 25 lb stack. (Which is quite reasonable.)

 

[rcgldr]

Simple experiement. Try lifting your body so that all your weight is on the bar, maybe try standing on it if you can balance yourself with a nearby object. Compare your weight to the weights on the scale.

If the back of the seat is tilted forwards, you could exert upwards force on the back of the seat. You could also jerk your body downwards, but would be quickly repelled back upwards.