# The discovery of the human body special mass

#### Yahya Sharif

Observations:
An average human of 60 kg can jump high and fast against gravity with legs muscles while he will barely move a rock of 60 kg with his all body muscles.
An average human of 60 kg can lift his body up holding a bar many times, but he will barely move the rock of 60 kg.
An average human can lift his body of 60 kg up like someone trying to pick a fruit from a tree many times with only his feet and calves' muscles but he will barely move a rock of the same mass with his all body muscles.
An average human can run fast with his massive 60 kg body while he will barely move an object with the same mass 60 kg.
Theory:
A muscle of a human or an animal can move or lift itself with force far less than the force needed to lift or move any other equivalent mass.
A human or an animal can move or lift the body with force far less than the force they need to move or lift any other object with the same mass. This is human muscle force on the human own body, so walking , running , walking upside down,etc are all effortless.
In such case of motion,i.e a human moves his own body like walking or running I can treat the mass as a smaller value in the equation f=ma and in this case the human will accelerate faster with mass m less than 60 kg.
Experiment:
A person stands on a scale. The scale reads his mass 60 kg *. Now this human moves up his body short distance like someone tries to pick a fruit from a tree. The scale will start to increase by small forces x N in which the total read of the scale is 600+x N. The force he exerts on the scale is x N. The force the scale pushes him up is also x N two forces in opposite directions. The force that lifts his body is the force the scale pushes him up which turned out to be the x N. For a force to lift an object it must be slightly greater than the object's weight.The force that lifts the person is x N. The person needed only x N to lift his body which is less than his weight 600 N. This is because the mass is lifted is a human mass.
*The scale shows mass 60 kg I converted it to force 600 N , force= mass* gravity acceleration gravity acceleration is 10 m/s^2

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petra4

#### Hayseed

"Theory:
A muscle of a human or an animal can move or lift itself with force far less than the force needed to lift or move any other equivalent mass."

It's not a theory, it's called mechanical advantage and has been known for centuries. A lever can move that rock just as easily with little force. The animal body is a series of levers.....that can be compounded. Insects too.

#### Yahya Sharif

"Theory:
A muscle of a human or an animal can move or lift itself with force far less than the force needed to lift or move any other equivalent mass."

It's not a theory, it's called mechanical advantage and has been known for centuries. A lever can move that rock just as easily with little force. The animal body is a series of levers.....that can be compounded. Insects too.
Let's say for the the experiment the foot is 20 cm or 0.2 meters long , Now let's calculate for a 0.2 lever:
First the lever will be class 3 :
The weight for 60 kg will be 60*10=600 Newtons.
Class 3 is the fulcrum at the toes , and in this case both the weight of my body and the force of my calves' muscles I lift my body with will be at the heel:
F: force of my weight
f: force of muscles strength
L: the distance of the weight from the heel to the toes.
l: distance of the muscles force from the heel to the toes.
f * l=FL
F=600 and L=l =0.2

f*0.2=600*0.2
f=600 Newton
The force needed to lift my body didn't change which is 600 N.
It is the same thing in jumping. The fulcrum of the lever will be at the knees, both my upper part body weight and my thighs' muscles force will be at the hip joint. The lever will then be class 3. I will need the same 600 N force to jump.
But as I said I can jump carrying a 600 N body fast against gravity with only legs muscles but I can't even move a rock of 600 N with all body muscles.

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petra4

#### Yahya Sharif

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 a 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.

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.

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. let's say we have a person of upper part 80 kg, this person does not carry any load. 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, and we both carry the same 80 kg load for me it is a rock plus my upper part, 40 kg upper part plus the rock I carry 40 kg or 80 kg, for the person it is his mere upper part of 80 kg.

When a mass to be lifted or moved is a human body it needs smaller force than lifting or moving any other equivalent mass. A human is lighter when walking, running, dancing, etc. A human needs bigger force to bear, move, lift other masses than bearing, moving , lifting a human own body.

petra4

#### Hayseed

What about momentum? Whenever you change the center of gravity, you create momentum. We glean bi-pedal motion from it. We modulate our momentum. Continuously. With our body levers.

There are many interactive dynamics to consider with a living body. Hard to compare with the dynamic of a rock.

#### Yahya Sharif

There are many interactive dynamics to consider with a living body. Hard to compare with the dynamic of a rock.
My comparison was jumping with leg muscles vs even moving the rock with whole body muscles including leg muscles. Think of someone lying on the floor pushing a wall with his feet and at the same time trying to move the rock this person uses his whole body muscles to push the rock yet it hardly moves compare it with high acceleration upwards against gravity when jumping with only leg muscle. An average human cannot throw a rock of 60 kg at that high acceleration even with his all body muscles but a human can do it with his body when jumping.

The experiment is a real life proof of a small force by weak feet and calves' muscles to lift the person many times. Feet and calves' muscles alone are weak however an average human"not body builder" can do exercise this way many times.
In general a human walks, runs, jumps, dances,etc easy with a massive 60 kg body mass.
Also the experiment gives an x N to lift a 60 kg human body mass, if the human is smaller like a child the x indeed will reduce.

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#### Hartmann352

Most people "can lift six to seven times their body weight," says Michael Regnier, professor and vice chair of bioengineering at the University of Washington. But most people don’t push themselves so hard, though athletes often push themselves more than most. Fear, fatigue and pain prevent people from attempting feats of amazing strength in daily life, says Dr. Javier Provencio, director of the neurological ICU at Cleveland Clinic.

Regnier, a former world-class weightlifter, has experienced bouts of incredible strength both as an athlete and as someone who helped after an accident. About 20 years ago, Regnier was driving on a Los Angeles freeway when he spotted a wrecked car on the side of the road. The driver sat slumped over his steering wheel so Regnier pulled over to help. It was instinct; he couldn’t fathom leaving the man without doing something. The driver’s door had caved in and Regnier couldn’t get him out any other way—he ripped the door off to pull the man out.

Regnier remembers his hands hurting from cuts he sustained while tearing off the car door, but he doesn’t know what happened with the driver because he left when the EMTs arrived.

Ripping doors off cars or lifting vehicles from people could be considered hysterical strength*. Little medical evidence exists about such cases; most of it remains anecdotal.

Physicians once believed that the adrenaline that flooded the system caused an extra boost to the muscles, allowing people to be stronger. But that’s not quite accurate. Adrenaline certainly primes the body for emergency action, it speeds up the heart and lungs, dilates the blood vessels and releases nutrients, both of which ready the muscles for quick responses.

And while the adrenaline fueled fight-or-flight reflex spurs people into action, the body’s entire stress response contributes to superhuman strength. Cascades of enzymes and proteins release, helping people sustain the activity.

* hysterical strength - The hysterical force, or super strength, or superhuman strength, is a demonstration of extreme strength, hypothetically outside human capacity, that is, beyond what is usually interpreted in the context of normality; in general, such manifestations occur in precarious situations between "life or death".

There are quite common anecdotal examples, such as those of certain mothers who have moved real vehicles to save their child stuck in the rubble or that passing truck driver who lifted an automobile off a victim..

The causes that support these manifestations are not completely clear, but it is hypothesized that they may be of a hormonal/chemical nature. To be precise, the implication of catecholamines should not be excluded; in practice, the hysterical force could be the cause of an uncontrolled discharge of adrenaline. Unfortunately, such situations are not repeatable, rather rare and use little evidence. Assuming that it is possible, the deepening of these phenomena is almost impossible.

It cannot be excluded that the expression of superhuman strength can be realized following the so-called "delirium of excitement".

During the "delirium of excitement" the glycolytic “Fast Twitch” Muscle, named so because of the high Speed it can cycle at, and vice verse for slow twitch, may produce less energy than the Oxidative “Slow Twitch” Muscle in total, but it produces more energy per second and much faster. Because it cycles faster, the things it can lift or whatever are much more than the slower cycling muscles. This is also why muscles ache after intense use.

Contrary to popular belief Lactate or rather Lactic Acid barely even affects muscle function. Rather, this arises when the Actin and Myosin Crossbridges are overstressed from so much activity or when the load is incrementally larger than the maximum force Myosin can give from latching on to the Actin Strip. As you might have guessed, Fast Twitch Muscle Cycles the crossbridging so fast that it overstresses their Myofibrils (The Containers the Actin and Myosin Bridges reside in) within mere seconds or slightly over a minute if the animal is built for it, exponentially much faster than Slow Twitch Muscles. Not only that, their Crossbridges are designed specifically for raw power but overlooks endurance, while Slow Twitch has Crossbridges that are much sturdier. In addition, the Metabolism this type of Muscle uses while faster at producing energy than slow twitch is really REALLY ineffecient. Not only does it produce a lot less energy in total, (Output of around 3-5 per 1 Metabolic activity as opposed to Oxygen related means yielding 35 energy for 1 Metabolic activity!), it produces lots of Lactate as an unwanted byproduct. Granted this doesn't affect the Muscle much, but it becomes the body's job to clear up the Lactate and with the amount of Lactate produced it has to work extra hard to do so. But the single fatal flaw it has is the requirements.

Oxygen related Metabolism in Muscles will eat just about anything and turn it into a TON of energy. You can even feed it fat directly and it's perfectly content with that. But not the Fast Twitch. In contrast, it greedily sucks up jaw dropping amounts of Glucose to power itself when it is exerting force on something. It doesn't accept anything besides Glucose or Glycogen. And it consumes so much of it yet produces laughable amounts of energy, albeit just faster than the other form of Metabolism. The huge amount of Glucose being sucked from your blood to power this soon takes a heavy toll on you. You feel very tired and want nothing more than to crawl into bed.

So, what happens when you are under the extreme life or death situations? We humans normally don't get to utilize our full strength. Our bones may be strong for our size and weight, but they would never be able to sustain the maximum capacity of our Muscles if we did that all the time. Normally we are kept from this in many ways. Our brain firstly restricts how hard each individual Myocyte, or Muscle Cell can pull. Almost never are we allowed to pull a single one at full force. Second, as a species we primarily have Slow Twitch Myocytes, so under normal conditions their Twitch would never be fast enough to sustain a heavy load. Third, our Central Nervous System never lets us use all our Myocytes, even when we try very hard to. Some signals are automatically cut and suppressed before our Muscles get them. Ever felt the time when you desperately tried to lift something heavy yet you couldn't, but never felt any pain? That's your recruited portion of Slow Twitch struggling to cycle hard and fast enough to lift said thing, but because Slow Twitch is very enduring you don't feel pain. But ever grabbed hold of a pull up bar and suddenly felt the searing pain in your arm after a while? Because you did manage to grab onto something your Slow Twitch cannot support, the Brain has to call in what little Faster Twitch Muscles are available. And those burn out really fast. Of course if you activated every single Slow Twitch and made each and every one of them pull to maximum force you would be able to do many things easily, but because of aforementioned reasons (CNS Restrictions) you cannot do so.

In an extreme situation however, all hell breaks loose pretty quickly. Suddenly the automatic system that yells “POWER BACK!!!” when you try to use force goes dead silent. Nothing is there to stop you now. Your Recruitment System now can use every single Muscle as it pleases, and as much as it wants to. This advantage is almost immediately evident as you realise you suddenly have no trouble throwing punches. Pain becones non existant. But the thing that truly makes Humans nearly 3 times stronger than they are isn't this. It's a very hacky solution from nature, but is extremely overpowered.

Fast Twitch is the strength wise better one. All animals are strong because they pack lots of Fast Twitch into a very dense bundle, and also because their Myosin and Actin Crossbridges are somewhat of a better quality than ours. When an animal gives it's all, it gets Epinephrine (Better known as Adrenaline) and Norepinephrine (A different variant of Adrenaline called Noradrenaline) to further increase it's strength, by numbing the effects of overstressed Crossbridges, temporarily increasing Glucose to an all time high so they have no trouble providing Glucose for the hungry Fast Twitch for a limited time, and also causing the Muscles to be a little more effecient and they hit harder than they usually do. But this is not the case with humans.

Nature took a huge gamble and designed Humans much differently. And what do you know? It worked! Instead of doing the same Fast Twitch trick like with other animals, Humans have a very hacky solution. Our Slow Twitch Muscles respond to Epinephrine much more prominently. It sends their Twitch Speed into Overdrive. The normally slow Oxidative processes suddenly acclerate so much that they reach the same speeds as the Fast Twitch ones, and even sometimes surpass them, with little to no decrease in energy. Suddenly Slow Twitch Muscles are cycling at such a speed that they don't even resemble Human strength. And if you remember, Slow Twitch Muscles eat just about anything, produces a crap ton of energy from so little substrate (Power source), and have Crossbridges much more durable than Fast Twitch.

What happens when you make them as fast as their counterpart? Chaos. Because they produce so much energy there's no danger of the Human running out of energy anytime too, because their Muscles aren't draining lots of Glucose from the blood, and because there's so much energy that means more can be used to propel the Myosin, which means they hit a LOT harder now. And because Slow Twitch Crossbridges can easily withstand stress forget about hoping that said Human’s Muscles will start to ache and burn. Now you have a Human who has near infinite stamina, and hits VERY hard. You're now going to be in a world of hurt unless you're a Bear.

We are already multiple times stronger than we actually need to be. We may be weaker compared to those Big Cats and Great Apes, but pretty much nothing else under or around our weight class with the exception of maybe Chimpanzees and Large Dogs including wolves can reliably win us in a fight. And even with Chimps and dogs or wolves, we can mess them up bad in return if they maul us. Mutual destruction, I'll take that over a complete loss. Just be grateful that nature was kind enough let us keep all this excess strength, otherwise we would be so Physically weak a tiny kitten could easily kill us!

See: https://www.nbcnews.com/healthmain/how-do-people-find-superhuman-strength-lift-cars-921457

See: https://www.quora.com/Is-hysterical-strength-real?share=1

See: https://en.energymedresearch.com/18045-hysterical-force

I used to lift weights for football and though I could lift a tremendous amount of weight years ago (curl 220 pounds, bench press 440 pounds and deadlift 670 pounds), I was always amazed at what I could accomplish while fighting fires in Broome County, NY. , when my adrenaline, glycogen and my slow twitch muscles were at a peak operation. I performed great feats of physical strength after casting my fear aside. Yet mine were in many cases no different in results - haul heavy water charged hoses into working fires and up extension ladders, pulling someone off the floor and tossing them over my shoulder - than the other firefighters I worked with. Yet the post dump let down was all too real and required time and some fluids to get going again.

#### Yahya Sharif

Most people "can lift six to seven times their body weight," says Michael Regnier, professor and vice chair of bioengineering at the University of Washington. But most people don’t push themselves so hard, though athletes often push themselves more than most. Fear, fatigue and pain prevent people from attempting feats of amazing strength in daily life, says Dr. Javier Provencio, director of the neurological ICU at Cleveland Clinic.
I have an experiment that proves the theory.
You can try it with any scale to find that the x is several Newtons less than 60 kg but it lifts the person, also feet and calves' muscles are weak and cannot provide a 60 kgf to lift the person. So it is logical that weak calves' muscles applies small x N to lift the body.
This is not an extraordinary force that a human can have in some body conditions. The feet and calves' muscles have a maximum force this is a fixed force. In case of the rock the human uses the maximum force of all body muscles and cannot move the rock. In the case of lifting as in the experiment the human uses only feet and calves' muscle and guess what he uses far smaller than the maximum because he can do an exercise like that many times.
Also the measurements are for an average human who has limited maximum force to lift objects. What if an average human is lying down on the floor pushing a wall with his feet and trying to throw the rock horizontally with his hands . The fact is, he will not be able to overcome friction to even move it, this case is with all body muscles now this average can throw his body at high acceleration against gravity with only leg muscles.
The maximum force of muscles of a human is usually fixed, he always lifts or jumps with force far smaller this happens all the time regardless of some extraordinary force a human can obtain in some conditions.
So, what about the experiment? what is the maximum x N force ? what it is specific maximum amount and why?

#### Hartmann352

Mr Yahya Sharif -

You might find the following of interest to you:

The muscular system is responsible for the movement of the human body. Attached to the bones of the skeletal system are about 700 named muscles that make up roughly half of a person’s body weight. Each of these muscles is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves. Muscle tissue is also found inside of the heart, digestive organs, and blood vessels. In these organs, muscles serve to move substances throughout the body.

Skeletal muscle is the only voluntary muscle tissue in the human body—it is controlled consciously. Every physical action that a person consciously performs (e.g. speaking, walking, or writing) requires skeletal muscle. The function of skeletal muscle is to contract to move parts of the body closer to the bone that the muscle is attached to. Most skeletal muscles are attached to two bones across a joint, so the muscle serves to move parts of those bones closer to each other.

Skeletal muscle cells form when many smaller progenitor cells lump themselves together to form long, straight, multinucleated fibers. Striated just like cardiac muscle, these skeletal muscle fibers are very strong. Skeletal muscle derives its name from the fact that these muscles always connect to the skeleton in at least one place.

Most skeletal muscles are attached to two bones through tendons. Tendons are tough bands of dense regular connective tissue whose strong collagen fibers firmly attach muscles to bones. Tendons are under extreme stress when muscles pull on them, so they are very strong and are woven into the coverings of both muscles and bones.

Muscles move by shortening their length, pulling on tendons, and moving bones closer to each other. One of the bones is pulled towards the other bone, which remains stationary. The place on the stationary bone that is connected via tendons to the muscle is called the origin. The place on the moving bone that is connected to the muscle via tendons is called the insertion. The belly of the muscle is the fleshy part of the muscle in between the tendons that does the actual contraction.

Skeletal muscles rarely work by themselves to achieve movements in the body. More often they work in groups to produce precise movements. The muscle that produces any particular movement of the body is known as an agonist or prime mover. The agonist always pairs with an antagonist muscle that produces the opposite effect on the same bones. For example, the biceps brachii muscle flexes the arm at the elbow. As the antagonist for this motion, the triceps brachii muscle extends the arm at the elbow. When the triceps is extending the arm, the biceps would be considered the antagonist.

In addition to the agonist/antagonist pairing, other muscles work to support the movements of the agonist. Synergists are muscles that help to stabilize a movement and reduce extraneous movements. They are usually found in regions near the agonist and often connect to the same bones. Because skeletal muscles move the insertion closer to the immobile origin, fixator muscles assist in movement by holding the origin stable. If you lift something heavy with your arms, fixators in the trunk region hold your body upright and immobile so that you maintain your balance while lifting.

Skeletal muscle fibers differ dramatically from other tissues of the body due to their highly specialized functions. Many of the organelles that make up muscle fibers are unique to this type of cell.

The sarcolemma is the cell membrane of muscle fibers. The sarcolemma acts as a conductor for electrochemical signals that stimulate muscle cells. Connected to the sarcolemma are transverse tubules (T-tubules) that help carry these electrochemical signals into the middle of the muscle fiber. The sarcoplasmic reticulum serves as a storage facility for calcium ions (Ca2+) that are vital to muscle contraction. Mitochondria, the “power houses” of the cell, are abundant in muscle cells to break down sugars and provide energy in the form of ATP to active muscles. Most of the muscle fiber’s structure is made up of myofibrils, which are the contractile structures of the cell. Myofibrils are made up of many proteins fibers arranged into repeating subunits called sarcomeres. The sarcomere is the functional unit of muscle fibers.

Sarcomeres are made of two types of protein fibers: thick filaments and thin filaments.
Thick filaments. Thick filaments are made of many bonded units of the protein myosin. Myosin is the protein that causes muscles to contract.

Thin filaments. Thin filaments are made of three proteins:

Actin. Actin forms a helical structure that makes up the bulk of the thin filament mass. Actin contains myosin-binding sites that allow myosin to connect to and move actin during muscle contraction.

Tropomyosin. Tropomyosin is a long protein fiber that wraps around actin and covers the myosin binding sites on actin.

Troponin. Bound very tightly to tropomyosin, troponin moves tropomyosin away from myosin binding sites during muscle contraction.

Skeletal muscles work together with bones and joints to form lever systems. The muscle acts as the effort force; the joint acts as the fulcrum; the bone that the muscle moves acts as the lever; and the object being moved acts as the load.

There are three classes of levers, but the vast majority of the levers in the body are third class levers. A third class lever is a system in which the fulcrum is at the end of the lever and the effort is between the fulcrum and the load at the other end of the lever. The third class levers in the body serve to increase the distance moved by the load compared to the distance that the muscle contracts.

The tradeoff for this increase in distance is that the force required to move the load must be greater than the mass of the load. For example, the biceps brachia of the arm pulls on the radius of the forearm, causing flexion at the elbow joint in a third class lever system. A very slight change in the length of the biceps causes a much larger movement of the forearm and hand, but the force applied by the biceps must be higher than the load moved by the muscle.

Nerve cells called motor neurons control the skeletal muscles. Each motor neuron controls several muscle cells in a group known as a motor unit. When a motor neuron receives a signal from the brain, it stimulates all of the muscles cells in its motor unit at the same time.

The size of motor units varies throughout the body, depending on the function of a muscle. Muscles that perform fine movements—like those of the eyes or fingers—have very few muscle fibers in each motor unit to improve the precision of the brain’s control over these structures. Muscles that need a lot of strength to perform their function—like leg or arm muscles—have many muscle cells in each motor unit. One of the ways that the body can control the strength of each muscle is by determining how many motor units to activate for a given function. This explains why the same muscles that are used to pick up a pencil are also used to pick up a bowling ball.

Muscles contract when stimulated by signals from their motor neurons. Motor neurons contact muscle cells at a point called the Neuromuscular Junction (NMJ). Motor neurons release neurotransmitter chemicals at the NMJ that bond to a special part of the sarcolemma known as the motor end plate. The motor end plate contains many ion channels that open in response to neurotransmitters and allow positive ions to enter the muscle fiber. The positive ions form an electrochemical gradient to form inside of the cell, which spreads throughout the sarcolemma and the T-tubules by opening even more ion channels.

When the positive ions reach the sarcoplasmic reticulum, Ca2+ ions are released and allowed to flow into the myofibrils. Ca2+ ions bind to troponin, which causes the troponin molecule to change shape and move nearby molecules of tropomyosin. Tropomyosin is moved away from myosin binding sites on actin molecules, allowing actin and myosin to bind together.

ATP molecules (adenosine triphosphate) power myosin proteins in the thick filaments to bend and pull on actin molecules in the thin filaments. Myosin proteins act like oars on a boat, pulling the thin filaments closer to the center of a sarcomere. As the thin filaments are pulled together, the sarcomere shortens and contracts. Myofibrils of muscle fibers are made of many sarcomeres in a row, so that when all of the sarcomeres contract, the muscle cells shortens with a great force relative to its size.

Muscles continue contraction as long as they are stimulated by a neurotransmitter. When a motor neuron stops the release of the neurotransmitter, the process of contraction reverses itself. Calcium returns to the sarcoplasmic reticulum; troponin and tropomyosin return to their resting positions; and actin and myosin are prevented from binding. Sarcomeres return to their elongated resting state once the force of myosin pulling on actin has stopped.

The strength of a muscle’s contraction can be controlled by two factors: the number of motor units involved in contraction and the amount of stimulus from the nervous system. A single nerve impulse of a motor neuron will cause a motor unit to contract briefly before relaxing. This small contraction is known as a twitch contraction. If the motor neuron provides several signals within a short period of time, the strength and duration of the muscle contraction increases. This phenomenon is known as temporal summation. If the motor neuron provides many nerve impulses in rapid succession, the muscle may enter the state of tetanus, or complete and lasting contraction. A muscle will remain in tetanus until the nerve signal rate slows or until the muscle becomes too fatigued to maintain the tetanus.

Not all muscle contractions produce movement. Isometric contractions are light contractions that increase the tension in the muscle without exerting enough force to move a body part. When people tense their bodies due to stress, they are performing an isometric contraction. Holding an object still and maintaining posture are also the result of isometric contractions. A contraction that does produce movement is an isotonic contraction. Isotonic contractions are required to develop muscle mass through weight lifting.

Muscle tone is a natural condition in which a skeletal muscle stays partially contracted at all times. Muscle tone provides a slight tension on the muscle to prevent damage to the muscle and joints from sudden movements, and also helps to maintain the body’s posture. All muscles maintain some amount of muscle tone at all times, unless the muscle has been disconnected from the central nervous system due to nerve damage.

Skeletal muscle fibers can be divided into two types based on how they produce and use energy: Type I and Type II.

Type I fibers are very slow and deliberate in their contractions. They are very resistant to fatigue because they use aerobic respiration to produce energy from sugar. We find Type I fibers in muscles throughout the body for stamina and posture. Near the spine and neck regions, very high concentrations of Type I fibers hold the body up throughout the day.

Type II fibers are broken down into two subgroups: Type II A and Type II B.
Type II A fibers are faster and stronger than Type I fibers, but do not have as much endurance. Type II A fibers are found throughout the body, but especially in the legs where they work to support your body throughout a long day of walking and standing.
Type II B fibers are even faster and stronger than Type II A, but have even less endurance. Type II B fibers are also much lighter in color than Type I and Type II A due to their lack of myoglobin, an oxygen-storing pigment. We find Type II B fibers throughout the body, but particularly in the upper body where they give speed and strength to the arms and chest at the expense of stamina.

Muscles get their energy from different sources depending on the situation that the muscle is working in. Muscles use aerobic respiration when we call on them to produce a low to moderate level of force. Aerobic respiration requires oxygen to produce about 36-38 ATP molecules from a molecule of glucose. Aerobic respiration is very efficient, and can continue as long as a muscle receives adequate amounts of oxygen and glucose to keep contracting. When we use muscles to produce a high level of force, they become so tightly contracted that oxygen carrying blood cannot enter the muscle. This condition causes the muscle to create energy using lactic acid fermentation, a form of anaerobic respiration. Anaerobic respiration is much less efficient than aerobic respiration—only 2 ATP are produced for each molecule of glucose. Muscles quickly tire as they burn through their energy reserves under anaerobic respiration.

To keep muscles working for a longer period of time, muscle fibers contain several important energy molecules. Myoglobin, a red pigment found in muscles, contains iron and stores oxygen in a manner similar to hemoglobin in the blood. The oxygen from myoglobin allows muscles to continue aerobic respiration in the absence of oxygen. Another chemical that helps to keep muscles working is creatine phosphate. Muscles use energy in the form of ATP, converting ATP to ADP to release its energy. Creatine phosphate donates its phosphate group to ADP to turn it back into ATP in order to provide extra energy to the muscle. Finally, muscle fibers contain energy-storing glycogen, a large macromolecule made of many linked glucoses. Active muscles break glucoses off of glycogen molecules to provide an internal fuel supply.

When muscles run out of energy during either aerobic or anaerobic respiration, the muscle quickly tires and loses its ability to contract. This condition is known as muscle fatigue. A fatigued muscle contains very little or no oxygen, glucose or ATP, but instead has many waste products from respiration, like lactic acid and ADP. The body must take in extra oxygen after exertion to replace the oxygen that was stored in myoglobin in the muscle fiber as well as to power the aerobic respiration that will rebuild the energy supplies inside of the cell. Oxygen debt (or recovery oxygen uptake) is the name for the extra oxygen that the body must take in to restore the muscle cells to their resting state. This explains why you feel out of breath for a few minutes after a strenuous activity—your body is trying to restore itself to its normal state.

There are four forces acting on the forearm and its load (the system of interest). The magnitude of the force of the biceps is
; that of the elbow joint is
; that of the weights of the forearm is
. Two of these are unknown (
and
), so that the first condition for equilibrium cannot by itself yield
. But if we use the second condition and choose the pivot to be at the elbow, then the torque due to
is zero, and the only unknown becomes
.

In the the biceps muscle, the angle between the forearm and upper arm is 90°. If this angle changes, the force exerted by the biceps muscle also changes. In addition, the length of the biceps muscle changes. The force the biceps muscle can exert depends upon its length; it is smaller when it is shorter than when it is stretched.

Very large forces are also created in the joints. In the previous example, the downward force
exerted by the humerus at the elbow joint equals 407 N, or 6.38 times the total weight supported. (The calculation of
is straightforward and is left as an end-of-chapter problem.) Because muscles can contract, but not expand beyond their resting length, joints and muscles often exert forces that act in opposite directions and thus subtract. (In the above example, the upward force of the muscle minus the downward force of the joint equals the weight supported—that is,
, approximately equal to the weight supported.) Forces in muscles and joints are largest when their load is a long distance from the joint, as the book is in the previous example.

The idea that your maximum force on the ground must equate your body weight is a misunderstanding that comes from the intuitive first assumption that forces always balance. Yes, forces balance in many situations, but not when acceleration is involved. If you can make the ground cause an acceleration, then the forces don't balance anymore.

See: https://physics.stackexchange.com/q...orce-you-can-exert-on-the-ground-with-one-leg

See: https://opentextbc.ca/openstaxcollegephysics/chapter/forces-and-torques-in-muscles-and-joints/

See: https://www.innerbody.com/image/musfov.html

Muscles are attached to bones by means of tendons. The maximum force that a muscle can exert is directly proportional to its cross-sectional area A at the widest point. We can express this relationship mathematically as F~max= σA, where σ (sigma) is a proportionality constant. σ is about the same for the muscles of all animals and has a numerical value of 3.0 × 105kg m−1s−2.
Hartmann352

#### Yahya Sharif

The idea that your maximum force on the ground must equate your body weight is a misunderstanding that comes from the intuitive first assumption that forces always balance. Yes, forces balance in many situations, but not when acceleration is involved. If you can make the ground cause an acceleration, then the forces don't balance anymore.
This is not true the maximum force to lift the object must be slightly greater than the weight , weight F=mg, m is the mass of the object:
An object of 100 N weight. Let's say I applied a 50 N on the object it will not move and while I increase the force it will still remain. When I reach the 100 N it will still remain because the net force I apply is zero, two equal forces 100 N in opposite directions. So I need to go beyond the 100 N by any force greater than 100 N to produce a non-zero net force upwards to lift the object. The force is actually the smallest number greater than 100 N which is actually cannot be determined so when using the scale you cannot know whether the force is equal to the weight 100 N or greater because any force like 100.000001 N can cause non-zero net force upwards and lift the object.

In the video the weight of the mass is 1.29 kg. First I measured the weight then I started from zero Newtons to lift the weight the force continue to increase while I am trying to lift the weight. As soon as the weight raises the force reached its maximum 1.29 kgf in this case by definition the force I need to lift the 1.29 kg is 1.29 kgf which is equal to the weight.*

Now, in the case of the human body lifting his body, he starts pressing the scale, the x continues to increase, as soon as his body raises he reaches a maximum of x N then by definition the force to lift the body is the x N.

This x force is not a random force, it is a specific maximum amount that is proportional to the human mass, If I repeat the lifting, as soon as my body raise I will get the same value if the human is a child of 25 kg the force in the scale to lift is smaller than x. So every human can lift his body with a specific force depending on his weight.

The x N force is the force that lifted the human body which is less than the weight 60 kg, in contrary of the physical concept that a force to lift a mass must be equal to the mass weight. This means a force smaller than the human body weight is sufficient to lift the body. What I mean is a human or an animal is an exception.

*actually it is the smallest force greater than 1.29 kgf or 1.29+f the resultant is 1.29+f-1.29 or f, f is the force upwards I need this force to create a non-zero net force upwards. But as it is tiny it does not appear in the scale instead the scale will read 1.29 kg.

Last edited:

#### Hartmann352

If you can jump off the ground on one leg then you have successfully exerted a force larger than your weight.

We can see this by just using Newton's second law: ∑𝑖𝐹𝑖=𝑚𝑎∑iFi=ma, where 𝐹𝑖Fi is one of the forces, 𝑚m is the mass of the person, and 𝑎a is the acceleration of the person

The two forces we are concerned with are the weight, 𝑤w, of the person, which acts downward, and the force 𝐿L applied by the leg, which acts upward on the person (technically you exert a force 𝐿L downward on the ground, but by Newton's third law the ground also pushes up on you with force 𝐿L).

If you merely raise your arm while standing on the floor, you will momentarily exert more than your own weight on the floor.

This experiment shows that a human particularly can lift his own body with force less than his weight:

A person stands on a scale. The scale reads his mass 60 kg *. Now this human moves up his body short distance like someone tries to pick a fruit from a tree. The scale will start to increase by small forces x N in which the total read of the scale is 600+x N. The force he exerts on the scale is x N*. The force the scale pushes him up is also x N two forces in opposite directions. The force that lifts his body is the force the scale pushes him up which turned out to be the x N. For a force to lift an object it must be slightly greater than the object's weight. The force that lifts the person is x N. The person needed only x N to lift his body which is less than his weight 600 N.

For every action there is an equal and opposite reaction.

Hartmann352

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