Homemade leg press

Okay, this device seems to suggest that multiple pulleys CAN be used to ratio up the effective weight. This advertisement suggests to me that I can load 210 lbs on the stack and then leg press 420 lbs., hence the 2:1 ratio. You guys agree?

It's been a long time since I've done pulley problems, and thus I cannot visualize the distribution of forces just by looking at the image. So, I'll look into this particular problem later, when I have some calculating time.
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Cheers.
 
Hey, thanks dkm. I was just logging on to post up my lastest thoughts on this. :D

At any rate, notice that the leg press attachment includes three pulleys with four cable lengths. This quadruples the force required to push the leg press lever. Put another way: if the cable tension is 100 lbs., then the force needed to push the leg press lever is 400 lbs. Thus, my vote is that it takes 400 lbs to lift the 100 lb weight.

Problem is: the advertisement tells us that it works on a 2:1 ratio. So, then, either I'm wrong or there's some more pulleys on the machine that aren't shown in the images.
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I see what you are saying, I guess I am going to have to crack open my old physics books, I simply do not remember how to equate the differing lines of force.
 
The only pulleys that affect the amount of force are the pulleys that are moving. So, the top pulley, and the two pulleys that are not on the actual lever don't change the amount of force, just the direction. The pulleys on the leg press move, so they change the amount of force. A single, (moving), pulley doubles the line pull, a second pulley would not double it again, but would add on double the initial amount, I think. So say the starting force is 100, adding one pulley gives you 200, adding another pulley gives you 300, a third gives you 400, etc. At least that's how I remember it :D

One thing to consider, each pulley adds friction, which makes the weight harder to lift, but easier to lower, which weakens the eccentric portion of the lift, not good for hypertrophy.
 
My guess is that in the leg press shown in the link, there is another pulley out of the photo that is attached to the weight stack that may actually help to lift the weight, so they need two pulleys on the leg press to get the 2:1 reduction. Since this is part of a larger machine, they may use an assistance pulley to reduce the effective weight for isloation excercises.
 
[b said:
Quote[/b] (Dood @ Aug. 27 2004,12:54)]The only pulleys that affect the amount of force are the pulleys that are moving. So, the top pulley, and the two pulleys that are not on the actual lever don't change the amount of force, just the direction. The pulleys on the leg press move, so they change the amount of force. A single, (moving), pulley doubles the line pull, a second pulley would not double it again, but would add on double the initial amount, I think. So say the starting force is 100, adding one pulley gives you 200, adding another pulley gives you 300, a third gives you 400, etc. At least that's how I remember it :D
One thing to consider, each pulley adds friction, which makes the weight harder to lift, but easier to lower, which weakens the eccentric portion of the lift, not good for hypertrophy.
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Thank you for that. Also good point on the eccentric.
 
[b said:
Quote[/b] (Dood @ Aug. 27 2004,10:54)]The only pulleys that affect the amount of force are the pulleys that are moving. So, the top pulley, and the two pulleys that are not on the actual lever don't change the amount of force, just the direction. The pulleys on the leg press move, so they change the amount of force. A single, (moving), pulley doubles the line pull, a second pulley would not double it again, but would add on double the initial amount, I think. So say the starting force is 100, adding one pulley gives you 200, adding another pulley gives you 300, a third gives you 400, etc. At least that's how I remember it :D

One thing to consider, each pulley adds friction, which makes the weight harder to lift, but easier to lower, which weakens the eccentric portion of the lift, not good for hypertrophy.
Click to expand...

Hmmmmm, that's not the way I remember it. :confused:

As I recall, the total force on the foot lever (or any other lever, for that matter) is divided amoung the number of cables that support the force. We could just forget about the pulleys for a moment and imagine that the cables are fastened to the foot lever. When we do this, it seems easy to see that there are four cables sharing the load, and thus we have a 4:1 ratio. If I'm incorrect, then what am I missing?
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You are correct in reference to the above diagram, my numbers were wrong.
However, as I said, I think the machine in the linked picture has another pulley, not in the picture, that gives a 2:1 advantage to the lifter, so that the 4:1 disadvantage on the leg press is needed to come up with the 2:1 ratio that they speak of for the leg press.
 
[b said:
Quote[/b] (Dood @ Aug. 27 2004,6:03)]However, as I said, I think the machine in the linked picture has another pulley, not in the picture, that gives a 2:1 advantage to the lifter, so that the 4:1 disadvantage on the leg press is needed to come up with the 2:1 ratio that they speak of for the leg press.
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Hi Dood,

Thanks much for taking a second look at this problem. I absolutely agree with you that there must be another pulley that's not in the picture, which results in the overall 2:1 ratio.

That's a very cool web site, by the way.
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New Max set on this machine
400Lbs my new 5 RM
See the two pics
 
[b said:
Quote[/b] (kid largo @ Oct. 05 2004,9:30)]how come u dont go to a gym dkm?
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Well, I don't need to.

Dark_Master, have you perfected or worked on your ideas at all. If so I would love to see them. I probably will be changing the set up on this machine and get the weights behind me, my wife actually sits behind me, she's there to call 911 in case the thing collapses, but so far it seems sturdy but with the weight constantly increasing it is getting a little scary so I am sure I'll change it. I'll repost the new pics when I'm done.
 
dkm-

I too have been very creative with piping to modify or create exercise equipment. I've been happy with a lot of my "experiments."

But when it comes to a leg press, leverage or otherwise, it is usually going to be more of a hip/glute/hamstring movement that allows one to move massive amounts of weight with little focus on the quads.

For years I have played games with every leg press, squat, safety squat, selectorized horizontal leg press, hack squat, leg extension movement trying to find the best quad exercise. Barbell squatting has always been difficult for me because of forward lean and lower back stress. I have a short torso and long legs.

For me the best solution I've found is the trap/shrug bar "squatlift" with heels elevated and rock bottom range of motion. http://www.exrx.net/WeightExercises/ErectorSpinae/TBDeadlift.html

Now I know many lifters will denounce the idea of elevated heels with a rock bottom range of motion because of the stress on the knees. But for me, the exercise does not allow my hips and glutes to start the movement. My quads must do all of the work to get out of the bottom position. That being said I can't lift a tremendous amount of weight, which spares the stress to my knees. Not to mention there is no stress on my lower back. And the tension on the quads is constant with no shift to hips or glutes. And raising my heels on a 2x4 eliminates most forward lean.

It also allows for the training of the quads with one of HST's principals of having the muscle loaded in the bottom stretched position. Most of the quad exercises out there are not going to give the same degree of stretch to the quad. (The leg press might, but with tons of weight it will stretch ones lower back in an extreme fashion.)

If you want to hit the glutes do hyper extensions, ham glute raises, or good mornings. For hamstrings leg curls or straight legged deadlifts.

If I were you I'd seriously consider a trap/shrug bar cage. They're fairly cheap to buy, but given your skills with piping and wood you could easily build your own custom unit. It would require less weight to load and would be a lot simpler, smoother, space efficient, and safer than your homemade leg press. You could also incorporate chains as mentioned earlier in this thread.
 
[b said:
Quote[/b] (lestat02852 @ Oct. 06 2004,2:48)]
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Thanks for the input. I still want to hit the glutes, I already do leg curls, I've tried GM's, Lunges, 1 Leg Squats, I will still use a leg Press of some sort simply because I can, but as I pointed to in another thread I am seriously thinking of DL, and yes with a trap bar most likely.
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Ah, alas not, DKm, I'm into squats... However I did convert my old York bench into a seated calf raise machine: To coin a phrase "the end comes off," and is replaced by a chest-pad. This is used during seated rowing and acts kinda like a "spider" row. (I'll post pics sooon)
As for havin' the old Moiety in attendance, why not get her to stroke your thighs whilst she's there... Then have her place her hands upon your traps/delts, and while you're leg pressing, she whispers in your ear to "relax your traps" - trust me it'll work...
Right as for the ol' trap bar - cheap to make & good to use... esp. after I modified my homemade one to incorporate both 1" and 2.5" grips, nice.

400lb leg press :D - we'll have to look into some Glute-ham raise machine designs...

The_dark_master
 
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