Long Arms VS Short Arms

[Yaad Mohammad]

Hey guys,

 

Today I came up with an interesting question. What differences does the length of your arms make when performing strength elements? I came up with a theory after doing some research on the subject.

 

First of all, I compared my full planche with someone who has remarkably longer arms. What I noticed is that the amount of lean required was significantly different between us. I had to lean much more than he had to. Of course many more factors play a role in this matter, but I still believe that it does make a difference. Longer arms mean that the angle between your wrist and arms becomes greater, meaning less lean. Here is the picture:

 

 

After doing some thinking I came to the following conclusion, longer arms make static straight arm holds like the planche, front lever and back lever significantly easier to hold. However, this is not the case with malteses and iron crosses, Coach Sommer explains this perfectly in this post:

 

Torque, or inch pounds, is determined by multiplying the applied force by the distance from the pivot point to the point where the force is applied.  For an iron cross, in plain english that means half the bodyweight times the length of the arm from the shoulder down to the wrist times two.

 

Given the angles involved between the upper arms and the torso the general equation for an iron cross is relatively straight forward;   

(sleeve length x half bodyweight) x 2 (you have two arms after all) = Inch pounds for an iron cross.  Obviously different people will have slightly different attachment points, but for a rough overall estimate of the forces involved the equation as is works fine.

 

The specific examples below should help you to clearly understand why the great ring men of the world have shorter arms; note that the 180lb gymnast with 21" sleeves needs to generate more than 1,000 additional in.lbs during an iron cross compared to the 150lb gymnast with 18" sleeves!  

 

It also provides a clear illustration as to why ring strength builds such incredible physiques; even though it appears that the gymnasts are "only" manipulating their bodyweight.

 

For a 150lb gymnast with 18" sleeves:

(18" x 75lbs) x 2 = 2,700 in.lbs

 

For a 150lb gymnast with 21" sleeves:

(21" x 75lbs) x 2 = 3,150 in.lbs

 

For a 180lb gymnast with 18" sleeves:

(18" x 90lbs) x 2 = 3,240 in.lbs

 

For a 180lb gymnast with 21" sleeves:

(21" x 90lbs) x 2 = 3,780 in.lbs

 

Yours in Fitness,

Coach Sommer

 

 

Furthermore, I believe moves such as push-ups, pull-ups or any other move that requires your arms to bend are also harder for people with longer arms. They have a much larger range of motion when performing these moves.

 

This is what I currently think. I’m interested in what you guys think about this subject.

[Daniel Burnham]

http://www.aaronswansonpt.com/basic-biomechanics-moment-arm-torque/

[Daniel Burnham]

Also in that picture your form is worse than the first.  In the top photo there is better protraction and the body is more level.  You are leaning over more and sinking in.

[Yaad Mohammad]

Also in that picture your form is worse than the first.  In the top photo there is better protraction and the body is more level.  You are leaning over more and sinking in.

That's true, but imagine his arms even longer, he'd have to lean even less when longer.

[Yaad Mohammad]

... but his body would probably be longer, too. Unless he's an orangutang or chimp.

My friend actually is 180cm but has a wingspan of 190cm. This guy is 183cm and has a wingspan of 187cm. So no, his body wouldn't need to be longer. I'm pretty sure that there are people out there who have an even bigger wingspan.

[Rikke Olsen]

Sorry, I deleted my previous post. Well, I'm no where near having a PL, and I've never had any arms but my own. Also, I don't do physics anymore (for a reason - I sucked), but things really also have to do with the length of your legs vs. torso.

 

So many factors are in play, I'd say it's pretty hard.

Also, wingspan is from fingertip to fingertip, right? What if he just has a broader chest? Longer fingers/bigger hands? Of course, this doesn't really have much to do with the case of longer arms/different angle, but I guess centre of mass is the key.

[Jono]

 

 

I got bored during revision for exams, so I did some analysis. And it seems that the arm length doesn't matter to the total torque.

 

First off, the centre of mass is always above the base of support. In this case, above the hands. Centre of mass can be seen as where the weight of a body acts. Torque (in an elementary sense) is defined as force * perpendicular distance to the pivot. In this case force = mg (mass * acceleration due to gravity), and the perpendicular distance to the pivot (with arm length L and angle x at the floor) is Lcosx. So the Torque = mgLcosx.

 

Now, assuming the guy suddenly grew longer arms with negligible mass gain, then his centre of mass would still be the same. The centre of mass still needs to be above the base off support, so the perpendicular distance to the shoulder joint still has to be the same. And since the mass is the still the same, so is the torque (= force * perpendicular distance).

 

Since Torque is the same as before but L increased, something else has to give. T=mgLcosx. But m is fixed, so cosx must have decreased to make up for it. Only way that happens is if the angle x increases, which is equivalent to less of a lean. But there's still the same torque overall.

 

What does this mean? Whilst the torque is the same, a different degree of lean would would obviously emphasize different muscles. More of a lean would place more torque at the shoulders (a shorter armed person), while less of a lean wouidn't place as much on the shoulders (longer armed person). Obviously these could affect the difficulty of the exercise depending on individual strengths.

 

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The only thing that definitely makes a planche harder (in terms of a larger torque sense) is if your centre of mass if further away from your shoulder joint. Somebody with heavy legs would fall into this category. As would somebody who is taller.

 

Bottom line: The length of the arms affects the degree lean required (which may emphasise different muscles, which could make it "harder" for one and not the other), but not the total torque. On the other hand, a centre of mass further away from shoulder will increase the torque, thus making it harder. With long arms usually comes a taller person, which usually involves a further displaced centre of mass. So really it's the displaced centre of mass that makes it harder, not the length of the arms/

 

What's interesting is that this only applies to planche, but not something like an iron cross

[Bill Köhntopp]

interesting topic here.

i could imagine that tensing a longer body is harder as with a shorter body, you know its a longer way to stabilize with muscles.

yeah and like mentioned, the centre of mass in relation to longer arms and legs will not be proportional i think, too.

[Daniel Burnham]

Good general idea. In reality the attachment points of the muscle and the length of the bones make a difference that isn't quantified by these simplistic hinge joint models. Pretty good approximation to get the idea though.

[Connor Davies]

I got bored during revision for exams, so I did some analysis.

Thanks for this.  I've wanted to see some rough equations for lever arm strength for a while now.

[Jono]

Thanks for this.  I've wanted to see some rough equations for lever arm strength for a while now.

No problem

 

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The calculated value of the torque on the shoulders should be pretty accurate. T=mgLcosx.

 

In order to hold a planche, one would have to apply an equal but opposite torque to stay static. So there will be some Force Required (from the muscles) * Some Distance (to the pivot) that must equal the same T as calculated above.

 

But it's these forces / distances to pivots that will vary due to attachment points of the muscle and the length of the bones etc. as Daniel said. So it's possible (and highly likely) that longer arms make a planche harder, despite them not having an intrinsic effect on overall torque.