Weightlifting shoe studies, and some physics

Suppversity just did a great article surveying various studies on weightlifting shoes and effectiveness.

What is most amazing about these studies, is that almost all of them measured output variables that no one cares about.

For example, one study measured affect on joint angles.  Joint Angles-- no, no, no!  People who buy and wear weightlifting shoes care about 2 things -  injury protection and LIFTING MORE.

How do we measure if a weightlifting shoe is going to help us lift more-- FORCE Output .

 AND,  how the shoe changes the distance of the bar from our center of gravity, such that we are able to lift more. This is sort of related to joint angles, but joint angles misses the mark-- I'll show you why, shortly.

So, if you're thinking of dropping money on a pair of weightlifting shoes, let's go over some basic physics:

1. Force = Mass x Acceleration
         To lift heavy stuff, you must generate a force by accelerating a mass
2. Energie or "work" = Force x Distance
         You create energy by acclerating the mass of the bar over a distance, such as when you pull, squat, or deadlift a bar
3.  Torque =  Force X lever arm distance x sine(of angle which force is applied, most cases its sine(90 degrees) which equals 1
     Torque is the expression of a force that causes rotation. The longer the lever arm distance the greater the torque. If the lever arm is equal to zero, then there is no torque or, rather, you can spin something freely about its center of mass.
     
Things that make you lift More  -- saving you from PR killers !

The oversimplified diagram in red shows a common technical mistake- keeping the bar far from the lifters center of gravity, increasing the amount of work the lifter needs to do to lift the weight.  The green figure shows that keeping the bar closer to the lifter makes the weight easier to lift!  Finally, the black diagram is a grossly oversimplified freebody diagram that, overall, shows that keeping the bar as close to the center of mass as possible will reduce unneeded torque on the bar, making it easier to lift.  *note, toque generated in the lifter's joints is a different subject.

As shown in the cartoon above, if the bar is unnecessarily far away from your body's center of gravity, there will be a greater torque on the bar that you will have to counteract by applying even more force.  This means , you can lift more if you reduce the torque because you will need to generate less force to lift the bar over head or to stand-up with it- as shown by the green figure.  This is true for both olympic lifts, the squat, and the deadlift. The further away the bar is from your body, the harder it will be to lift-- AND the more stress it will put on your spine!

Note --In both cases, the lifter generates force by pushing their feet into the ground.

So, how does this relate to weightlifting shoes, 3 things:

1. A solid heel that minimally compresses will increase force ouput to the ground.

2. A shoe with a stable outsole -- toebox and heel --will also reduce energy lost from poor lateral stability.
-- many weightlifting shoe brands have solid heels, few have a stable toebox. This makes the difference between lifters with feet that barely move (good) and feet that wobble (bad).

3. A shoe with the right heel height will enable the lifter to keep the bar even closer to their center of gravity.
--- This reduces the torque arm

Now, you can measure these cumulative effect of these 3 items by simply measuring force and distance of the bar from the lifters Center of gravity (CG).    As one example, Force can be measured by having a lifter lift on a force plate or load cell.   The distance of the bar from the CG can be measured with optics , also, as one example.

Just for fun, I did an anlysis on a lifter using optics.  $0 was spent on this 15minute study =0. The results, however, give you a good idea of  what actual scientific studies SHOULD HAVE DONE.

The subject lifter's anatomy is as such their torso, upper leg, and their lower leg are all about the same length. That means, their tibia/fibia is about as long as their femur,   and the length of their torso is about half the length of their entire leg (upper leg + lower leg).  There are many lifters with similar body types, whereas a torso that is shorter than the total length of the leg gives a stability advantage in the squat position of the snatch and the clean.

They were asked to do a squat with the same weight in 4 types of foot wear treatments - 1 ) in wood heel Risto weightlifting shoes, 2) in plastic heel nike romaleos 3, 3) in normal sneakers or tennis shoes with almost no heel rise, 4) barefoot.  Many on the internet would say that nike's are the best of the Plastic heel shoes and that the Risto's are the best of the wood heel shoes.

I did not take force measurements since the funding for this study was $0 and 15minutes ;) .

Optics were done with ImageJ software.

Note, the actual measurment lines in the software are not shown. Lines shown are for visual guidance.

The results were quite interesting. As expected, lifting barefoot kept the bar furthest from the center of gravity, which means lifting barefoot makes squatting heavy weights more difficult. It's also interesting to see the lifter's back is the most rounded when squatting barefoot.   The tennis shoes and nike's were almost equal.  The tennis shoes actually seemed to edge out the nike's with respect to distance from center of gravity, but the difference in camera angle may have contributed some error. The back angle looks better in the nike's than in the tennis shoes.  The Risto sports weightlifting shoes had the best bar spacing to center of gravity out of the 4.  The back position of the lifter looks best in the Risto's as well.

In terms of force output, this was not measured. The two weightlifting shoes would undoubtedly win out because of better lateral stability and less compressibility of the heel. The nike had a softer toebox than the risto, so it is possible that the softer toebox could equal bigger force losses.  This would be a good follow-up study to do.

Again, the $0 15min study does have error sources* in it.  What we can really get out of this experiment is that weightlifting shoes are far better than lifting barefoot and (the correct shoe) is better than lifting in tennis shoes.

UPDATE- one comment received is my oversimplification of the bar-lifter system.  As mentioned above , this is a very over-simplifed analysis.

 A more complete model would be seen by applying control theory and modeling the lifter in State Space.

This research paper does just that:  Optimization of Barbell Trajectory During The Snatch Lift Technique By Using Optimal Control Theory Shahram Lenjan Nejadian, Mostafa Rostami and Farzad Towhidkhah Biomedical Engineering Faculty, Amirkabir University of Technology (AUT), 424 Hafez Ave

Here is a more complete description of the lifter's angles:

Snip from: Optimization of Barbell Trajectory During The Snatch Lift Technique By Using Optimal Control Theory Shahram Lenjan Nejadian, Mostafa Rostami and Farzad Towhidkhah Biomedical Engineering Faculty, Amirkabir University of Technology (AUT)

Here is a  model in state space showing more appropriate non-linear equations to model the weightlifter during the snatch. A similar approach can be taken for the squat:

From: Optimization of Barbell Trajectory During The Snatch Lift Technique By Using Optimal Control Theory Shahram Lenjan Nejadian, Mostafa Rostami and Farzad Towhidkhah Biomedical Engineering Faculty, Amirkabir University of Technology (AUT), 424 Hafez Ave

The above isn't actually the full set of derivations. Basically, they do model the torque in the system looking at the Center of gravity of the bar and the lifter. They discuss optimization of torque generated by each of the joints. They discuss optimal bar paths, which --GUESS WHAT-- optimize the drift of the bar from the lifter's centerline (kind of like my crude little diagram above ;).

 Overall, if we did a more complex model we could model the drift in technique relative to the lifter using different shoes.   It's  all similar principles.

We can posit that the over-simplified  $0 15minutes study  does show a benefit of wearing weightlifting shoes.  Weightlifting shoes can help keep the bar closer to your center of gravity, hence , enabling you to lift more with less force - everyone's goal ! =)

The author has 0 ownership or affiliation with the 3 brands tested.

* error sources- variation in camera angle, repeatability of imagej software, order lifter lifted in each treatment. May want to consider doing additional bodytypes.