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Old 08-17-2012, 01:03 PM   #11
Tannhauser
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Quote:
Originally Posted by kitarpyar View Post
Apart from the absolute value of the weight lifted, beyond a point of time there's also a diminishing strength return with increasing bodyweight (although strength DOES increase) - this makes it easier for lighter guys to lift x times their bodyweight than bigger guys. Therefore for "best lifter" comparisons, Wilks coefficients are widely used in a powerlifting meet.

Mathematically, Wilks coefficient (comparing relative strength of PL) is given by the following formula:

coeff = Wt lifted / (a + b*x + c*x^2 + d*x^3 + e*x^4 + f*x^5)

Here x is the bodyweight and a-f are constant values (different for men and women). As you can see, the variation is non-linear. The normalized weight is this factor multiplied by the weight lifted.

Here's a graph I plotted out (lol, I have nothing better to do at lunch time), which shows the variation of normalized weight with bodyweight if the lifters lift 2x bodyweight.

Lifting 2x stronger at a higher bodyweight would have you much stronger compared to a lower bodyweight using the normalized scale.



In your example, normalized weight lifted by the 180 lb lifter lifting 360 lbs would be 242.712. The same value for the 350 lb guy lifting 600 would be 327.9
Interesting. I was trying to figure out why this should be. Is this something to do with scaling? I'm not at all sure I can explain myself, but let's try some (very) hypothetical figures:

Let's say a lifter is like a cube with 0.5 m sides, and a density of 1000kg/m cubed. And he has a thigh muscle 0.1m * 0.1m (= 0.01 m sq) that can lift 200kg.

His mass is 125kg, he can lift 200kg, so strength/ mass is 1.6

Now double him in size in every dimension. He is now 1m * 1m * 1m = 1 metre squared, which means he now has a mass of 1000kg (well, I said it was hypothetical).

However, his thigh, if it has increased in proportion to his other dimensions, is now 0.2m * 0.2m = 0.04 m sq. in cross-sectional area. It's four times bigger than it was.

Now, strength of muscle is directly proportional to cross sectional area (other factors being equal), so therefore he can now lift four times as much = 800kg.

An eightfold increase in mass has resulted in a four fold increase in muscle cross sectional area, so his strength/mass ratio is now 800/1000 = 0.8, half what it was before.

The ratio will change because mass is proportional to the cube of length, whereas strength is only proportional to the square. Poorly expressed, but that's my best shot.
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Lifetime PRs

Powerlifts: 500/363/573 @ 220 belt only
front squat: 403
dips: bodyweight + 176 x 4
military press: 232

Last edited by Tannhauser; 08-17-2012 at 01:06 PM.
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