Biomechanics question from the peanut gallery

I’m given to understand that **one ** reason great apes are physically stronger than humans has to do with the location of muscle attachments. The idea being that the farther (further?) down the bone you place the muscle insertion, the greater the leverage and thus the more power you can employ from a given quantity of muscle.

This dangerously inadequate piece of information has Inigo’s mind whirling with plans to stop tha show in the 2008 Olympic weightlifting competition.

Using a simple motion like a biceps curl, let’s say I can curl 100 lbs without blowing a gasket. If I had someone relocate the insertions of both my biceps 2 inches further down my (ulna?) Could I expect to realize a significant gain in usable power? Any idea as to how much? (I expect similar modifications would need to be made further (farther?) up on both shoulders to work in concert with the movement).

Would a doctor do this just because I asked for it or would that violate some oath or law?
Would the OIC disallow my competing due to such an alteration? It’s not doping.

Not anything useful to add. I believe it is called kinesiology, not biomechanics.

The reattachments of tendon to bone would take forever to heal, require a great deal of physical therapy, and in the meantime, your limb would be mostly useless. And there’s no guarantee they would ever attach to the new locations with enough strength to allow such feats of strength.

It’d be far easier to just perform weightlifting training and consume buttloads of steroid precursors like everyone else.

Hey, a question right up my alley!
Well…your information is not entirely correct…the main reason a chimp is proportionaly stronger than a human has more to do with their muscles are made. Without getting too technical, a muscle is stronger when it has more of the proteins that pull along each other inside a muscle cell that cause a contraction.
Now, let’s assume, though, that they also rely on the mechanism you describe. The reason a muscle attached further down the bone casn appear to be stronger has to do with moments. A moment is a force times a distance (F x d). The smaller the force, or smaller the distance, the less of an opposing moment is needed to lift the weight. Since, in theory, the attachment of the muscle is permanent, the old way to make it easier to lift is to make the muscle more able to oppose the moment, i.e., make you capable of providing a bigger force. But, let’s assume you can change the position of the muscle. We’ll do some simple math.

We have to lift a 100 lb. barbell. For the sake of simplicity, we’ll assume only the bicep acts to do the lifting (this is a gross simplification, but dealing w/ multiple muscles is hard.) So, if the length of your forearm is 13", and the bicep is attached 1" after the elbow. That leaves us wth 12", and 100 lbs. That works out to 100 ft-lbs that your muscle has to provide to lift the bicep.

If we move the muscle’s point of insertion one inch further down, we have (100lbs)(11/12) = 91.6 ft-lbs. If we move it two inches down we need to provide (100)(10/12) = 83 ft-lbs.

Not a big difference, really. Also, it’s practically impossible…and probably against the hippocratic oath, so my advice: start working out and taking a lot of creatine.
BS in Biomedical Engineering, concentration in mechanics
(see, I told you it was right up my alley :stuck_out_tongue: )

(And Dog80, it’s also called biomechanics. I hope it is, at least, cause that’s the course I took that gave me most of the knowledge i used to answer this question.)

I like the twisted way **Inigo Montoya ** thinks.

But why stop with conventional surgeries to relocate tendons and ligaments? What if you could further tinker with the human frame in such a way as to augment and multiply the sites for muscle attachment to bone, by growing more bone? (A lot more bone!) Forget human growth hormone – go for the gold – genetic engineering-induced neurofibromatosis (Elephant Man’s Disease)! After a few years, you won’t even recognize your old self! :dubious:

The muscle itself exerts a force, not a moment, and the force is what Inigo is trying to reduce. Sum moments about the elbow. The weight exerts a moment of 100*13 = 1300 in-lb. The bicep force thus has to provide a moment of 1300 in-lb to hold the weight. If the biceps insertion is originally one inch from the elbow, it has to exert (1300 in-lb / 1 in) = 1300 lb. If it could be moved two inches farther down, it would only have to exert (1300 in-lb / 3 in) = 433 lb, which is a two-thirds reduction in force.

There are probably some drawbacks (aside from the medical difficulty of moving the biceps insertion), but they are not obvious to me. You still have to do just as much work to lift the weight a given distance.

Wow…2/3 reduction in needed force. That sounds like I’m now curling 300 pounds! I’m a tough kid–I’ll deal with the rehab & PT.

Now for the rest of it.

Would a doctor do this just because I asked for it or would that violate some oath or law?
As **bouv ** pointed out the Hyppocrats would probably cease to dig the chili of the doctor who gets involved. But is this in fact the case? Is it that much different from cosmetic surgury.

Would the OIC disallow my competing due to such an alteration? It’s not doping.
Probably after I sweep up all the gold they’ll kick in a surgical modification rule (I’ve also kicked around the idea of sprinters surgically removing “excess” weight–some ribs, a kidney, half the small intestine–diet supps & IV feeding would make life livable, maybe both arms at the elbow…) But for now, is there any rule that this violates the spirit or letter of?

There is one drawback I hadn’t thought of - muscles have a natural resting length, so if you did have the insertion moved, you’d never be able to fully extend your arms. You would look like “Hans and Franz” all day, every day. Except you’d have that Olympic gold around your neck! Let us know how it goes!

Ooh, you reminded me of something else. In addition to having a resting length, they have an optimal length at whcih they provide the best force. That is to say, since your muscle is already streched out a little bit, that actually makes it harder to contract it back.

So, if at the normal muscle attachement position, we are at L[sub]0[/sub], 100% of muscle length. If we strech it out, what happens is the proteins that pull along each other to form a contraction are more seperated, less of them are touching, and therefore less of them can grab on to each other to cause a contraction. If your bicep is 7" long, and you turn it into 9" by moving the point of insertion 2" further down, then the muscle is now 128% the length it used to be. According to Figure 9-5 in Human Physiology (Varner, Sherman, and Luciano, 9th edition) a muscle 128% it’s orginal length will only be able to provide ~60% of it’s maximum isometric tetanic tension.

So, if originally you could only lift 100 lbs, we see by Hyperelastic’s math that the muscle has to provide 1300 lbs to be able to lift it. So we’ll assume 1300 lbs is the maximum tension your muscle can provide. 60% of 1300 lbs is 780 lbs. Now, again, from Hyperelastic’s math, if the point of insertion is 2" further down, your muscle only needs to provide 433 lbs to lift 100 lbs, but, in theory, you could have lifted 300 lbs, since you could have provided the full force (1300 lbs) times the distance (3") to oppose up to 300 lbs times 13". But now, you can provide 780 lbs times 3", equals 2340 in-lbs. Divide that by the 13" from the elbow to the barbell, and your maximum curling weight is 180 lbs.

So, in the end, you increased the amount you can lift by 80%. If we add another inch to the point of insertion, then your maximum becomes ~200 lbs. So the more you increase the point of insertion, the less you add to your maximum lifting weight, and eventually you start to left less. Add one more inch, and you are now at the same point as before, a maximum of 100 lbs. Move the insertion point any further, and you become weaker.

Oh, and I need to add a :smack: for messing up in my math. I always seem to make stupid mistakes like that, hence why I only got a B in biomechanics. :mad: