Forum
>
Image Themes
>
Thread
Log in |
Register
Not really possible to compare Leg Press, Hack Squat and Pull-down cause every machine is different, lifts that are measureable need to be free weight such as Strict Barbell Curl, Dumbbell Bench Press, Dumbbell Shoulder Press, Barbell Overhead shoulder press, or anything that uses barbells or dumbbells...
Not really possible to compare Leg Press, Hack Squat and Pull-down cause every machine is different, lifts that are measureable need to be free weight such as Strict Barbell Curl, Dumbbell Bench Press, Dumbbell Shoulder Press, Barbell Overhead shoulder press, or anything that uses barbells or dumbbells...
Came here to say this. Leg presses and hack squats on different machines are very difficult to compare unless you do a fair bit of work.
Some leg press machines have you move a plate horizontally, which lifts a stack vertically. In those, the weight is roughly whatever the stack weight is.
Some have a plate which slides up at a 45 degree angle. In that case the weight is the weight of the plates plus the weight of the sled (generally unknown unless you know the machine model and look up the specs), times sin(45) = 0.707. Typically the sled weighs 100-ish pounds (but can vary significantly, probably +- 50 lbs), so take the plate weight plus 100 lbs or so, then multiply by 2/3 to 3/4. I'm guessing most of the leg press machines that can be loaded down with 500+ pounds of plates probably have sleds on the higher end of that range.
Hack squat machines are similar to the above, but you're also pushing up roughly half to 2/3 of your body weight, plus the weight of the sled. Same deal: plate weight, plus sled weight, plus 1/2 to 2/3 of the lifter's body weight, times 2/3 to 3/4.
Finally, some leg press machines have the weights move in an arc. These have a variable force curve, generally set up so that the weight is less at the bottom of the rep (where you have the greatest mechanical disadvantage) and greatest toward the top of the rep (i.e. toward lock-out). Thus there isn't a constant tension.
In other words, very difficult to compare.
And comparing leg presses to squats is even more fraught. Of course there's the bar weight (generally 45 lbs for the empty bar plus the plates, although some bars are different). But if you want to compare to a leg press, you also have to add about 2/3 to 3/4 of the lifter's weight, since most of their body above the knee is being lifted as well (if you work out the math, it's nearly 100% of the waist-up mass, plus about 50% of the upper leg mass).
But even then, a squat is an entirely different animal as it's a free-weight movement. There are balance and stability issues, plus the squat also recruits the core to stabilize the torso. A Smith machine squat is a bit more analogous, but Smith machine squats suck since they force your body to adapt to the weights, rather than vice versa. And even then, squats (both free weight and Smith) recruit much more heavily from the posterior chain, particularly with a wider stance, but even with a narrower stance since the hip goes into full extension (which doesn't happen with most leg presses).
One final point about the leg press videos is that there is a wide variation in movement depth. You can do way more weight if you only do half-reps when it comes to squats and leg press.
Most movements have a characteristic point at which failure is most likely to occur, based on where you are most mechanically disadvantaged.
In the case of squats and leg presses, for example, that usually happens near the bottom, i.e. at the position of maximum muscular elongation. That is where you will almost certainly fail, so you can do more weight, or more reps, if you don't go to full depth. These sort of movements can fail catastrophically if you don't see it coming (i.e. you need to know whether you have another rep in the tank before you reach depth, because if not you aren't coming back up and will need a safe way to bail).
In some other cases (such as pull-ups, pull-downs, and rows), the point of maximum mechanical disadvantage occurs near the "top," i.e. at the position of maximum muscular contraction. Usually on these exercises you don't "fail," you just realize that you can't reach maximum contraction anymore although you can still do the bottom half to 2/3 of the rep easily.
In some others the point of failure occurs near the middle of the movement. Standing biceps curls are the obvious example, so the way to avoid failure here is to use momentum to swing the weight through the middle position (when your forearm is horizontal and the weight is moving vertically).
Bench press is somewhere between the first and third. The sticking point is usually a little above the bottom of the movement, although for some people it's closer to the lockout (in which case triceps accessory work can be a great help).
Collecting a table of the heaviest lifts on this site.