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The human body weight force on human body joints


awaterpon
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The human joints bear an average human body of 60 kg for years without joints damage. Let's say the body above the knees for a human is 40 kg. An average human knees bear a 40 kg body above the knees for years without knees damage. If an object like a rock of 40 kg is fixed to the upper part, the knees will bear the rock of 40 kg for a short period of time, minutes, hours, days, before the knee's damage. The time the knees bear the upper part with no rock is years, the time the knees bear the body with the rock is several hours. First the knees bear 40 kg upper part for years, then the knees bear a double of 80 kg for hours. Even though the mass doubled, the time of bearing must double as well, but it actually multiplies by years or thousands of hours which is a very big number compared to only several hours.
 
The force of human upper part on the knees is very small compared to the force of any object of the same mass on the knees. That why human walks on his knees carrying his upper part for years, but he walks on his knees carrying an object of the same mass for only several hours.
1) I have an upper part of 60 kg and I lift a rock of 60 kg :
I put the rock on stomach and back equally, I have 60 kg upper part before putting the rock and 120 kg after putting the rock. The period of time my knees bear the rock plus my upper part or 120 kg can be approximately 5 hours. The time my knees bear when I remove the rock should not exceed approximately 10 hours because I removed half of the load. But when I remove the rock, the time my knees bear is years. I left with upper part body alone, and human knees bear a 60 kg human upper part for years. This difference in time is because a human body alone presses knees with tiny force and this tiny force make knees bear this upper part for years even though the bearing should not exceed 10 hours
The difference between knees bearing 60 kg upper part for years and knees bearing 120 kg for 5 hours is very big.
 
2) I have an upper part of 40 kg and I lift a rock of 40 kg :
I put the rock equally on back and stomach. The total weight I carry is 80 kg, it is the rock 40 kg plus my body above the knees 40 kg. Now we have a person of upper part 80 kg, this person does not carry any load. I will lift a load of 80 kg, which is my upper part 40 kg plus the rock 40 kg, the person will lift an 80 kg load which is his mere upper part.
Carrying a rock of 40 kg" 40 kg rock plus my upper part 40 kg or 80 kg" for a day will damage the knees. However, the person's knees do not injure even if he carries his upper part of 80 kg for many years.
Edited by awaterpon
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I'm having trouble following this (and wondering where the average human body weighs 60 kg... are you writing this from the Kalahari,  or a fashion runway in Milan??).   Are you suggesting that all people have the same sized joints?   A slightly-built person carrying a heavy boulder is not analogous to, say,  a heavily-built Swedish peasant just carrying himself,  even if the knee loads are the same.   

Any load that you didn't grow into,  and which is somewhat cantilevered out from your body's core,  will obviously stress the knees more.   We're descended from fairly lean hunter-gatherers,  and our joints evolved to handle the loads imposed by our lean body mass reached around ages 15-20.  And there's a little extra, for sudden acceleration and deceleration forces so we can jump around,  run,  and haul water and game, etc.   But just carrying a 40 kg rock around for extended periods is likely something only a few outliers can achieve without joint stress.  That's what motivated us to develop sleds,  travoises, carry-poles, and many other methods to gain biomechanical advantage. 

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2 hours ago, swansont said:

Beyond that, I have no idea what you are trying to say. Clarification is needed.

 

In other words replacing the body above the knees with any other object will press much harder than the body does both the body above the knees and the object have the same mass. That why the knees can bear mere body for years but if replaced by any other equivalent object the knees will fail after few hours. 

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4 minutes ago, awaterpon said:

 

In other words replacing the body above the knees with any other object will press much harder than the body does both the body above the knees and the object have the same mass. That why the knees can bear mere body for years but if replaced by any other equivalent object the knees will fail after few hours. 

There’s no reason to think this is true, and probably no evidence you can provide.

How would the knee know the nature of the mass providing this weight?

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12 minutes ago, awaterpon said:

 

In other words replacing the body above the knees with any other object will press much harder than the body does both the body above the knees and the object have the same mass. That why the knees can bear mere body for years but if replaced by any other equivalent object the knees will fail after few hours. 

No. Read the post by @TheVat. The difference is that a 40kg rock is not aligned with the skeleton to load it in the same way as body weight would. Furthermore it is dead weight, unlike body weight, which is a mass of bone, fat and muscle that moves dynamically in response to the action of walking. 

Both things make a huge difference to how the knees and other joints are loaded, during the action of walking or other movements.  

(It is noteworthy that people used to carrying heavy loads in many parts of the world choose to place them on their heads. This will be because having the extra load taken by the spine is the best way to avoid off-centre loading of the joints.)  

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1 hour ago, swansont said:

How would the knee know the nature of the mass providing this weight?

The knees do not press, the mass does. The object presses normal but the body knows what it presses, if it his own knees it will press slightly so the human survives with such massive 40 kg.

1 hour ago, exchemist said:

No. Read the post by @TheVat. The difference is that a 40kg rock is not aligned with the skeleton to load it in the same way as body weight would. Furthermore it is dead weight, unlike body weight, which is a mass of bone, fat and muscle that moves dynamically in response to the action of walking. 

Both things make a huge difference to how the knees and other joints are loaded, during the action of walking or other movements.  

(It is noteworthy that people used to carrying heavy loads in many parts of the world choose to place them on their heads. This will be because having the extra load taken by the spine is the best way to avoid off-centre loading of the joints.)  

Think of a human jumps 5 years, walk 40 years, stand 30 years, run 20 years ..... How the alignment will help him to do all of this carrying a massive body of 40 kg for 70 years ? and think of the rock aligned perfectly as the body , the force on the knees still the weight of the rock which is massive for the knees to bear for hours

Edited by awaterpon
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11 hours ago, swansont said:

Provide evidence of this claim. Not assertion. Evidence.

The whole human body functions through signals carried by the nervous system from the brain to  the heart, digestive system, lungs,etc and knows how the  processes should work . If I cut off my arm, the arm will no longer be part of the body and can be treated as an ordinary object no signals on it, if I lift it it will press the knees just like the rock, and although it is human body on human body " upper part on knees "lifting another human will also behave as the rock because the other human is not part of the body.

Edited by awaterpon
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