Efficiency of the human body as a machine
The human body may be quite efficient in producing high-energy ATP from food, when there is adequate oxygen(32% efficiency), in preventing wear and tear, from friction when bones, muscles and tendons slide over each other to effect motion or change the direction of force, through synovial fluid, which is a secretion from the bursa; but not so in the overall work output. This is because, once released, the unused energy from ATP is never recaptured in any other useful form for reuse but is rather dissipated(wasted) as heat.
A machine is a combination of rigid or resistant bodies, formed and connected so that they move with definite relative motion or transmit force from the source of power(effort) to the resistance to be overcome(load). This function requires strength and rigidity. A machine has two functions: transmitting definite relative motion and transmitting force. Simple machines include the wedge(double inclined plane), levers which include pulleys/belts on wheels or merged toothed wheels(gears) and the screw jack, which is an inclined plane(less effort is put in to move a load, the weight assisting).
The human body achieves both functions of a machine, through contraction of muscles, which are firmly attached to rigid bones, connected by wedged, hinge or ball-in-socket joints and effect or prevent movements about these joints. Movements about the joints include bending(flexing), stretching, rotation, or sideway movements about the mid line(abduction and adduction).
Because of the relative weak stability of the joints and weakness of the bones, muscles, ligaments and tendons and low mechanical advantage of our limbs due to the long distance of the load, they carry in the hand or foot, from the joint pivot, when compared with the point of application of the effort, from the contraction of say the biceps, nearer the joint; the human body is not a very good machine.
Due to low mechanical advantage, more effort is needed to do unaided manual work. In moving the parts of the body, no work is done in the strict sense of the word(work output=0) as potential energy gained by movement against gravity is lost as the body parts return to the resting position i.e net movement is zero(there is effort but no work). As we walk, air resistance is negligible, so no work is done i.e load is zero. However, work is done when we lift objects and keep them at that potential(against gravity) due to the effort from the contraction of our muscles fueled by ATP and the distance covered. As we relax, following the effort, there is passive return and reattachment of actin and myosin muscle filaments. The stronger the muscle tone, the more the efficiency of work, as more efficient filament interactions are made. This explains why a trained athlete will sweat less profusely than the uninitiated, after a brisk exercise. An untrained athlete easily suffers from exhaustion(ATP energy use-up) and fatigue (inability to produce effort as evidenced by increased extracellular potassium, exuded from the muscle). Developing muscle tone through exercise can significantly increase efficiency in human mechanics, through good canalization of ATP-produced energy, with little interference between the filaments that occurs in a slack muscle. Performance is also significantly enhanced by increase in filaments mass through cross-linkage/synchrony and greater muscle force, with little effort.
There are some ways the body is adapted to increase mechanical advantage: the knee cap moves upwards towards the hip, during stretching of the leg, facilitating the shortening of the hip quadriceps muscles(increasing force output, assisting effort) during lifting of a load with the leg.
Fortunately, many vital activities in the body depend on mere physical quantities: the air pressure in the lungs falls after expiration, letting in a gust of air from the high atmospheric pressure outside, thereby saving energy resources of respiratory muscles. These muscles mostly come in support when there are signs of respiratory distress. During the filling phase of the cardiac cycle, the heart muscle stretches and during emptying the muscle recoils as a spring. The potential spring energy being converted into kinetic energy is utilized to pump blood. This is the basis of Starling's law. Of course, ATP-mediated cardiac contraction is responsible for most of cardiac force.
Due to the low effort at rest, the human body is more efficient in its utilization and conservation of energy resources, hence the advocacy for a sound sleep, bed rest, good mental predisposition in the healing process. Regular exercise tones up the muscles, and renders our physical activities, breathing and heart function more efficient. We can prevent many diseases by training our muscles to function more efficiently.
Dr Oliver Verbe Birnso, M.D.
A machine is a combination of rigid or resistant bodies, formed and connected so that they move with definite relative motion or transmit force from the source of power(effort) to the resistance to be overcome(load). This function requires strength and rigidity. A machine has two functions: transmitting definite relative motion and transmitting force. Simple machines include the wedge(double inclined plane), levers which include pulleys/belts on wheels or merged toothed wheels(gears) and the screw jack, which is an inclined plane(less effort is put in to move a load, the weight assisting).
The human body achieves both functions of a machine, through contraction of muscles, which are firmly attached to rigid bones, connected by wedged, hinge or ball-in-socket joints and effect or prevent movements about these joints. Movements about the joints include bending(flexing), stretching, rotation, or sideway movements about the mid line(abduction and adduction).
Because of the relative weak stability of the joints and weakness of the bones, muscles, ligaments and tendons and low mechanical advantage of our limbs due to the long distance of the load, they carry in the hand or foot, from the joint pivot, when compared with the point of application of the effort, from the contraction of say the biceps, nearer the joint; the human body is not a very good machine.
Due to low mechanical advantage, more effort is needed to do unaided manual work. In moving the parts of the body, no work is done in the strict sense of the word(work output=0) as potential energy gained by movement against gravity is lost as the body parts return to the resting position i.e net movement is zero(there is effort but no work). As we walk, air resistance is negligible, so no work is done i.e load is zero. However, work is done when we lift objects and keep them at that potential(against gravity) due to the effort from the contraction of our muscles fueled by ATP and the distance covered. As we relax, following the effort, there is passive return and reattachment of actin and myosin muscle filaments. The stronger the muscle tone, the more the efficiency of work, as more efficient filament interactions are made. This explains why a trained athlete will sweat less profusely than the uninitiated, after a brisk exercise. An untrained athlete easily suffers from exhaustion(ATP energy use-up) and fatigue (inability to produce effort as evidenced by increased extracellular potassium, exuded from the muscle). Developing muscle tone through exercise can significantly increase efficiency in human mechanics, through good canalization of ATP-produced energy, with little interference between the filaments that occurs in a slack muscle. Performance is also significantly enhanced by increase in filaments mass through cross-linkage/synchrony and greater muscle force, with little effort.
There are some ways the body is adapted to increase mechanical advantage: the knee cap moves upwards towards the hip, during stretching of the leg, facilitating the shortening of the hip quadriceps muscles(increasing force output, assisting effort) during lifting of a load with the leg.
Fortunately, many vital activities in the body depend on mere physical quantities: the air pressure in the lungs falls after expiration, letting in a gust of air from the high atmospheric pressure outside, thereby saving energy resources of respiratory muscles. These muscles mostly come in support when there are signs of respiratory distress. During the filling phase of the cardiac cycle, the heart muscle stretches and during emptying the muscle recoils as a spring. The potential spring energy being converted into kinetic energy is utilized to pump blood. This is the basis of Starling's law. Of course, ATP-mediated cardiac contraction is responsible for most of cardiac force.
Due to the low effort at rest, the human body is more efficient in its utilization and conservation of energy resources, hence the advocacy for a sound sleep, bed rest, good mental predisposition in the healing process. Regular exercise tones up the muscles, and renders our physical activities, breathing and heart function more efficient. We can prevent many diseases by training our muscles to function more efficiently.
Dr Oliver Verbe Birnso, M.D.
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