Hand size punching power

jeremyemilio said:
Yup.

Wow.

And I thought Matt was just overestimating the significance of torque v momentum.

No wonder we can't get on the same page.
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The thing is....his calculation actually supports my claim, despite the snide remark. Surely it's a simplification, but the basic principles of this problem are all there.
 
bunchof66 said:
bunch of science dorks in here with interesting stuff to say about physics (for real, good stuff guys) but it's all pretty irrelevant i think

technique plays a bigger part than any but the most drastic physical differences will.

for instance, footwork >>>>> fist size.

i think the closest factor first size is gonna is that (iirc) big hands could be indicative of a thicker bone structure, which would mean the fighter has much less risk of breaking their hands and can not only punch with reckless abandon during the fight but also during training.

for more about that read the article about pacquiao's wrist size. he's got 8 inch circumference wrists. for some perspective i am 6'6" and mine are 7.5"!
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And after all of that, this is the correct answer, of course.

(Although wrist size is more relevant in boxers as they throw fewer looping punches and are much more skilled at kinetic linking.)

The reality is, if you really want to KO someone, hit him with a shot he doesn't see coming.
 
Matt4786 said:
The thing is....his calculation actually supports my claim, despite the snide remark. Surely it's a simplification, but the basic principles of this problem are all there.
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No it doesn't.

As he stated, this calculation assumes that the entire body is being swung by some other force... which is a hell of a long way from being a 'simplification' for describing the action of a fist and arm being swung by the body.

If you could swing your entire 180 lb body at someone with the same velocity as a regular strike, every punch would be a knock out punch!
 
jeremyemilio said:
No it doesn't.

As he stated, this calculation assumes that the entire body is being swung by some other force... which is a hell of a long way from being a 'simplification' for describing the action of a fist and arm being swung by the body.

If you could swing your entire 180 lb body at someone with the same velocity as a regular strike, every punch would be a knock out punch!
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The problem he solved says nothing about swinging, only the moment of inertia. The angular momentum of the actual swing is reflected in the product of moment of inertia and angular velocity. We have already considered angular velocity to be equal. Your entire body does go behind a strike (assuming you know what you're doing), with different parts having different contributions based on distance from the axis of rotation (which should be somewhere in your core). The parts closer to the axis have a more significant contribution than those further away based on mass. The difference in radius doesn't overcome this. The velocity varies, but the angular velocity does not.
 
Even given the most optimistic assumptions, the effect of varying the size of a person's hands (at least within a normal human rage) is negligible. Not sure why this is even worth arguing about to be honest...
 
If anything, having bigger hands just usually correlates to bigger arms, shoulders, torso, etc. The whole mass thing really doesn't sound like it would hold up because its not like the extra how ever many ounces from a slightly bigger hand is enough to start knocking everyone out.

You can easily say does having bigger forearms help? Maybe. More mass. Do bigger shoulders help? Maybe. More mass. And just go all the way down the line. Its not like having bigger hands is the single hidden secret to power. There are many other factors.
 
Matt4786 said:
The problem he solved says nothing about swinging, only the moment of inertia. The angular momentum of the actual swing is reflected in the product of moment of inertia and angular velocity. We have already considered angular velocity to be equal. Your entire body does go behind a strike (assuming you know what you're doing), with different parts having different contributions based on distance from the axis of rotation (which should be somewhere in your core). The parts closer to the axis have a more significant contribution than those further away based on mass. The difference in radius doesn't overcome this. The velocity varies, but the angular velocity does not.
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You need to recalculate.

Start with the shoulder at the axis and the fist at the furthest point from the axis. The rest of the body is definitely generating force through kinetic linking... but it has no business in this calculation.

We already know that bigger fighters are generally stronger and are thus able to generate more force and that proper technique is even more important.

But we are trying to isolate fist size as a factor. We can't isolate it altogether because, as you rightly suggested earlier, that would assume the fist is being swung on a string. So we add the entire arm, calculate it's momentum based on its weight relative to the axis, and then apply two different masses at the end of that arm.

Throwing the rest of the (relatively) stable (and sometimes backwards or sideways moving) body into the calculation makes it impossible and virtually worthless even if it was possible.

How do you even determine the length of the rod? Where is the axis? Where is the radius? Are you calculating weight from behind the axis into the equation for angular momentum?

It just doesn't make any sense.
 
jeremyemilio said:
You need to recalculate.

Start with the shoulder at the axis and the fist at the furthest point from the axis. The rest of the body is definitely generating force through kinetic linking... but it has no business in this calculation.
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If the shoulder is the axis, it's a crappy punch, and in that case, I would say hand size matters. For a well-thrown punch, the body is very much a factor, and has business here.

jeremyemilio said:
We already know that bigger fighters are generally stronger and are thus able to generate more force and that proper technique is even more important.

But we are trying to isolate fist size as a factor. We can't isolate it altogether because, as you rightly suggested earlier, that would assume the fist is being swung on a string. So we add the entire arm, calculate it's momentum based on its weight relative to the axis, and then apply two different masses at the end of that arm.

Throwing the rest of the (relatively) stable (and sometimes backwards or sideways moving) body into the calculation makes it impossible and virtually worthless even if it was possible.

How do you even determine the length of the rod? Where is the axis? Where is the radius? Are you calculating weight from behind the axis into the equation for angular momentum?

It just doesn't make any sense.
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It makes sense, it's just a simplification, since you would guess that integrating a human body is problematic. The rest of the body is not stationary, which is why I think you're confused. When throwing a hook, the entire body is rotating.

I estimate the rod to be about a meter, maybe a bit longer (distance from spine to hand), but I think he did it a bit too long TBH. He also forgot to divide a term by 2 (the moment of inertia for the hand), but that's not all that important.


Now if the guy is punching while moving backward, throwing a straight with no body behind it, then hand size might matter, but these are rarely KO punches as it is and we're talking about guys who know how to put their mass behind strikes, not just their arms.
 
Matt4786 said:
edit. Obroin's calc was better, but still proves the general point, even if it's a vastly simplified approach.
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Alright we're getting to the bottom of this. Our calculations haven't even come close to approximating the situation. Your calculations assumed point particles with I=mr^2, and the problems with mine were already discussed.

Robbie Lawler is credited with a 188 cm reach (1.9m). Cut that in half, and now were talking a 0.95 m radius for the fist. Now, lets assume he weighs 180 lbs (80 kg), as described earlier. The problem with our approach is that most of that weight is centered in his torso/legs/head. The arms are a very small percentage of total weight (5.7% of TBM according to ExRx). So we will let one arm be 6% of TBM, or 4.8 kg. Now, I have roughly 6 inches (15 cm) between the center of my sternum and my shoulder. So the remaining 70 kg is centered in a "disk" (if you view it from above) of radius 15 cm.

So lets calculate the moment of inertia of 3 different segments. 1) the arm 2) the body and 3) the additional weight at the fist.

1) mass density p1 = 4.8/0.8 = 6

I = p1/3 (0.95^3 - .15^3) = 1.7

2) Moment of inertia of a disk I = 1/2 * m * r^2 = .5*70*.15^2 = 0.7875

So from here we can already see the arm has a much greater moment of inertia than the body (almost twice as much). Now lets do the fist.

3) I = .1kg * .95^2 = 0.09 (11% of the body inertia)

Now, that doesn't seem like much, but that means that the extra 100g at the fist has 11% of the inertia of the 70 kg in the body. AND that's assuming that all 70 kg is used to generate a moment of inertia, which is impossible. Assuming that 100g is rather small on the total natural variation, it shows that that hand size is pretty significant.
 
GrantB13 said:
If anything, having bigger hands just usually correlates to bigger arms, shoulders, torso, etc. The whole mass thing really doesn't sound like it would hold up because its not like the extra how ever many ounces from a slightly bigger hand is enough to start knocking everyone out.

You can easily say does having bigger forearms help? Maybe. More mass. Do bigger shoulders help? Maybe. More mass. And just go all the way down the line. Its not like having bigger hands is the single hidden secret to power. There are many other factors.
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No, no, no. You don't swing the shoulder. You swing FROM the shoulder. You can't factor in the size of my ballsack when estimating my punching power (although, interestingly enough, you could legitimately factor it in when estimating my ability to deliver a body check).

You can count the forearm, but the fist is the impact area and goes through the greatest range of motion, meaning it accelerates fastest, and travels at the highest velocity. Therefore the relative weight of the fist is more significant.

Why do so many of you want to insist that punching someone while holding a roll of quarters in your fist is no different from punching someone while you have that same roll of quarters in your pocket?

I get that physics can be tough, but come on. It's not THAT tough.
 
obroin said:
Alright we're getting to the bottom of this. Our calculations haven't even come close to approximating the situation. Your calculations assumed point particles with I=mr^2, and the problems with mine were already discussed.

Robbie Lawler is credited with a 188 cm reach (1.9m). Cut that in half, and now were talking a 0.95 m radius for the fist. Now, lets assume he weighs 180 lbs (80 kg), as described earlier. The problem with our approach is that most of that weight is centered in his torso/legs/head. The arms are a very small percentage of total weight (5.7% of TBM according to ExRx). So we will let one arm be 6% of TBM, or 4.8 kg. Now, I have roughly 6 inches (15 cm) between the center of my sternum and my shoulder. So the remaining 70 kg is centered in a "disk" (if you view it from above) of radius 15 cm.

So lets calculate the moment of inertia of 3 different segments. 1) the arm 2) the body and 3) the additional weight at the fist.

1) mass density p1 = 4.8/0.8 = 6

I = p1/3 (0.95^3 - .15^3) = 1.7

2) Moment of inertia of a disk I = 1/2 * m * r^2 = .5*70*.15^2 = 0.7875

So from here we can already see the arm has a much greater moment of inertia than the body (almost twice as much). Now lets do the fist.

3) I = .1kg * .95^2 = 0.09 (11% of the body inertia)

Now, that doesn't seem like much, but that means that the extra 100g at the fist has 11% of the inertia of the 70 kg in the body. AND that's assuming that all 70 kg is used to generate a moment of inertia, which is impossible. Assuming that 100g is rather small on the total natural variation, it shows that that hand size is pretty significant.
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I think there's a flaw in your calculation using density. I don't think your units are correct. Inertia should be a squared term, not a cubed term. You need to derive radius-dependent mass from that density, and then do the integral. You are doing the integral based on density itself when you need to use mass. That's why you have such a large value for the arm. You are also forgetting to divide your antiderivatives by 2. I'm not saying you are outright wrong, but your calculations look off.
 
Makes a difference but not really the main factor, having strong quads, obliques, anterior delts, triceps and forearms will make a bigger difference. Hardest hitters are guys who are both stocky and also stupidly fast (think Tyson)
 
Matt4786 said:
I think there's a flaw in your calculation using density. I don't think your units are correct. Inertia should be a squared term, not a cubed term. You need to derive radius-dependent mass from that density, and then do the integral. You are doing the integral based on density itself when you need to use mass. That's why you have such a large value for the arm. You are also forgetting to divide your antiderivatives by 2. I'm not saying you are outright wrong, but your calculations look off.
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They are squared. The integral of a moment of inertia is given as {p(r) r^2 dV. Assuming density is constant (with the units kg/m) you can pull it outside of the integral,and then when you integrate r^2, you get (1/3) r^3. So, the units now become kg/m * m^3. The meters in the denominator cancel out one in the numerator, so it becomes a squared term.
 
Another thing, people always mention big arms, theres no doubt having bigger arms means more weight to swing about for punching, but remember the upper arm muscles (biceps / triceps) dont move the upper arm, only flex / extend the elbow.
 
If the force behind the punch is equal, then the smaller the hand is, the greater the pressure/impact inflicted on the target!
 
obroin said:
They are squared. The integral of a moment of inertia is given as {p(r) r^2 dV. Assuming density is constant (with the units kg/m) you can pull it outside of the integral,and then when you integrate r^2, you get (1/3) r^3. So, the units now become kg/m * m^3. The meters in the denominator cancel out one in the numerator, so it becomes a squared term.
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You're right. Hand size contributes more than I would have thought. 11% is not negligible. Nice work.

On second thought, shouldn't you be dividing density by a volume rather than a length? I'm not so sure you are correct anymore. Nevermind. You are right. I am rusty as fuck at calculus.

Edit: actually, you forgot to divide the last term by 2, so it's more like 5%. Which still matters, but not as much.
 
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Matt4786 said:
You're right. Hand size contributes more than I would have thought. 11% is not negligible. Nice work.

On second thought, shouldn't you be dividing density by a volume rather than a length? I'm not so sure you are correct anymore. Nevermind. You are right. I am rusty as fuck at calculus.
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Haha no worries man, it was fun and a good debate.
 
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