[Yahya A.Sharif (OP)]

Three or four times their body weight?

Like I said, you have the data (a child might be expected to carry his twin brother) but you do not understand it.

Why not a rock of 120 kg or 160 kg?

[Bored chemist]

Do you think the child's twin weighs 120Kg?

[Bored chemist]

Do you understand that it is easier to carry things n a backpack, than in your arms?
Do you understand why?

[alancalverd]

It is an odd fact that people experience more difficulty lifting dead weight than live weight - including corpses that were alive a few minutes earlier. I  think the reason is that a live or even partially conscious load has an instinctive tendency to "help" by arranging its muscles to distribute the interface pressure as evenly as possible, so no single upper body muscle group is carrying the entire load. But the fact remains that the bearer's legs are transmitting the entire load plus the bearer's weight, to the ground. 

[Yahya A.Sharif (OP)]

Do you think the child's twin weighs 120Kg?

You said he can lift four times his own weight. If he weighs 40 kg, then carrying 160 kg (40 + 120) would match that claim. But realistically, a child weighing 40 kg would struggle to carry even a 40 kg object-like a rock-upstairs. Why is that?

[Bored chemist]

Why is that?

Did you not read this, or not understand it?

It is an odd fact that people experience more difficulty lifting dead weight than live weight - including corpses that were alive a few minutes earlier. I  think the reason is that a live or even partially conscious load has an instinctive tendency to "help" by arranging its muscles to distribute the interface pressure as evenly as possible, so no single upper body muscle group is carrying the entire load. But the fact remains that the bearer's legs are transmitting the entire load plus the bearer's weight, to the ground. 

How about this?

Do you understand that it is easier to carry things n a backpack, than in your arms?
Do you understand why?

We keep telling you the answer and you just ask the same question.
Why do you do that?

[Bored chemist]

Do you think the child's twin weighs 120Kg?

You said he can lift four times his own weight. If he weighs 40 kg, then carrying 160 kg (40 + 120) would match that claim. But realistically, a child weighing 40 kg would struggle to carry even a 40 kg object-like a rock-upstairs. Why is that?

Which part of this do you not understand?
Please go through it nd point out the bit that you do not accept or do not understand?
A (typical, reasonably fit) 70Kg man can reasonably be expected to carry a second man of the same (70Kgf) weight while walking, even up stairs.
While walking, each leg takes the load in turn.
So, half the time the whole load of man (70Kgf)  plus the twin (another 70Kgf)  is on the left leg. So, we know the left leg can carry 140Kg
And half the time that load - man (70Kgf)  plus the twin (another 70Kgf)  is on the right leg.
So, we know that each  of two legs can carry 140 Kgf
And he can use both of them, so his legs  can lift 280Kgf between them.
Of that, rather less than 70 Kgf is the person's top half.
So we know that he can (if he uses both legs) lift rather more than 280Kgf-70Kgf.

He can lift more than 210Kgf
So, more than 3 times his weight

[Yahya A.Sharif (OP)]

Did you not read this, or not understand it?

It is an odd fact that people experience more difficulty lifting dead weight than live weight - including corpses that were alive a few minutes earlier. I  think the reason is that a live or even partially conscious load has an instinctive tendency to "help" by arranging its muscles to distribute the interface pressure as evenly as possible, so no single upper body muscle group is carrying the entire load. But the fact remains that the bearer's legs are transmitting the entire load plus the bearer's weight, to the ground. 

I'm not convinced by this argument. What if the living person is completely relaxed, just like a dead body-would that make a difference? A person can move their own body using biomechanical advantage, and when carrying another living person, that body effectively becomes an extension of their own. In such cases, biomechanical advantage can still be applied.

[alancalverd]

Just try it, or talk to nurses and operating theater staff. Nobody is saying that a dead body weighs more than  live one, it's just a lot more difficult to lift!

[Yahya A.Sharif (OP)]

This experiment offers further verification of the presence of a biomechanical advantage in human movement:

A male subject weighing 57.7 kgf stands on a scale and performs a calf lift, reaching a peak force output of 59.2 kgf. The net force responsible for the upward acceleration of the body-acting through the toes-is measured at 1.5 kgf. The corresponding force exerted by the Achilles tendon is calculated as:

F = (13 / 5) * 1.5 = 3.9 kgf

The actual acceleration during the lift can be estimated using the kinematic equation:

a = 2x / t^2

Where:
x = vertical displacement (0.1 m)
t = time duration (0.2 s)

Substituting the values:

a = (2 * 0.1) / (0.2^2) = 5 m/s^2

This means the subject achieves an upward acceleration of 5 m/s^2. However, a force of only 3.9 kgf (≈ 38.2 N) acting on a 57.7 kg body would, without any mechanical advantage, produce an acceleration of:

a = F / m = (3.9 * 9.8 ) / 57.7 ≈ 0.66 m/s^2

The significant discrepancy between the actual acceleration (5 m/s^2) and the expected acceleration from direct force application (0.66 m/s^2) highlights the role of a biomechanical advantage.

Experiment
Full Paper

[Yahya A.Sharif (OP)]

This research was recently accepted as an abstract at the International Union of Physiological Sciences (IUPS) 2025 Congress.

[Bored chemist]

This experiment offers further verification of the presence of a biomechanical advantage in human movement:

A male subject weighing 57.7 kgf stands on a scale and performs a calf lift, reaching a peak force output of 59.2 kgf. The net force responsible for the upward acceleration of the body-acting through the toes-is measured at 1.5 kgf. The corresponding force exerted by the Achilles tendon is calculated as:

F = (13 / 5) * 1.5 = 3.9 kgf

The actual acceleration during the lift can be estimated using the kinematic equation:

a = 2x / t^2

Where:
x = vertical displacement (0.1 m)
t = time duration (0.2 s)

Substituting the values:

a = (2 * 0.1) / (0.2^2) = 5 m/s^2

This means the subject achieves an upward acceleration of 5 m/s^2. However, a force of only 3.9 kgf (≈ 38.2 N) acting on a 57.7 kg body would, without any mechanical advantage, produce an acceleration of:

a = F / m = (3.9 * 9.8 ) / 57.7 ≈ 0.66 m/s^2

The significant discrepancy between the actual acceleration (5 m/s^2) and the expected acceleration from direct force application (0.66 m/s^2) highlights the role of a biomechanical advantage.

Experiment
Full Paper

Re "A male subject weighing 57.7 kgf stands on a scale and performs a calf lift, reaching a peak force output of 59.2 kgf. "
That is proof that a body can be lifted by a force grater than the body's weight.
59.2 is bigger than 57.7

You just showed that your claim is false.

Are you going to stop now?

[alancalverd]

The response time of a bathroom scale is inadequate for the purpose of this demonstration.

[Yahya A.Sharif (OP)]

The response time of a bathroom scale is inadequate for the purpose of this demonstration.

The response time in the experiment was acceptable, and the accuracy is strong. The following four experiments help validate the concept:

1. Calf Muscle Force: The maximum pushing force generated by the calf muscles is lower than expected especially in children and average people, suggesting an underlying biomechanical advantage rather than raw force alone.


2. Abdominal Weight Support: A human can support an average weight of 60 kg on the abdomen without pain or injury, whereas far lighter external loads can cause discomfort. As noted by Bored Chemist, this is likely because when one human supports another, the supported body acts as part of the same system, allowing biomechanical leverage to come into play.


3. Lifting Living vs. Dead Bodies: Living bodies are easier to lift than dead ones. This is because the living person can effectively becoming an extension of the lifter's body and activating biomechanical leverage.


4. Calf Push and Acceleration: During a calf raise, the upward acceleration of the body exceeds expectations even when the force output is relatively low-such as 3.9 kgf-indicating enhanced efficiency through mechanical advantage.

[Yahya A.Sharif (OP)]

This experiment offers further verification of the presence of a biomechanical advantage in human movement:

A male subject weighing 57.7 kgf stands on a scale and performs a calf lift, reaching a peak force output of 59.2 kgf. The net force responsible for the upward acceleration of the body-acting through the toes-is measured at 1.5 kgf. The corresponding force exerted by the Achilles tendon is calculated as:

F = (13 / 5) * 1.5 = 3.9 kgf

The actual acceleration during the lift can be estimated using the kinematic equation:

a = 2x / t^2

Where:
x = vertical displacement (0.1 m)
t = time duration (0.2 s)

Substituting the values:

a = (2 * 0.1) / (0.2^2) = 5 m/s^2

This means the subject achieves an upward acceleration of 5 m/s^2. However, a force of only 3.9 kgf (≈ 38.2 N) acting on a 57.7 kg body would, without any mechanical advantage, produce an acceleration of:

a = F / m = (3.9 * 9.8 ) / 57.7 ≈ 0.66 m/s^2

The significant discrepancy between the actual acceleration (5 m/s^2) and the expected acceleration from direct force application (0.66 m/s^2) highlights the role of a biomechanical advantage.

Experiment
Full Paper

Re "A male subject weighing 57.7 kgf stands on a scale and performs a calf lift, reaching a peak force output of 59.2 kgf. "
That is proof that a body can be lifted by a force grater than the body's weight.
59.2 is bigger than 57.7

You just showed that your claim is false.

Are you going to stop now?

When standing still, the subject is not actually supporting the full 57.7 kg of body weight in the way we typically assume. Similarly, during upward acceleration, the subject is not exerting a full 59.2 kgf of force. For example, when lying prone on the abdomen, the body does not bear the entire 57.7 kg load directly on that surface - it supports much less. This explains why there is no pain or injury in such a position.

[Bored chemist]

As noted by Bored Chemist, this is likely because when one human supports another, the supported body acts as part of the same system, allowing biomechanical leverage to come into play.

Liar.
I did not say that.
I said the opposite, people can hold other people up simply because people are a lot stronger than you seem to understand..

[Yahya A.Sharif (OP)]

As noted by Bored Chemist, this is likely because when one human supports another, the supported body acts as part of the same system, allowing biomechanical leverage to come into play.

Liar.
I did not say that.
I said the opposite, people can hold other people up simply because people are a lot stronger than you seem to understand..

That explanation is not your own, but you did mention that a person can support another person. My question is: why can someone support another person weighing 60 kg on their abdomen, but not a 60 kg object like a rock?

[alancalverd]

Pressure, not force, determines tolerability. Another human is flexible and self-adjusts to minimise mutual pressure by maximising contact area. Bare feet are more tolerable than the same bloke wearing rigid boots.

[alancalverd]

The response time in the experiment was acceptable,

Not to a physicist or engineer.

[Bored chemist]

That explanation is not your own,

Then you should not have pretended it was, should you.

Anyway, are you really to stupid to understand padding?
People are soft; rocks are hard.