Wednesday, June 4, 2014

The Reason for the Loss of Bone Mineral Density in Space (weightless environment - microgravity) and on the Earth

Loss of Bone Mineral Density in Space (weightless environment – microgravity)

The absence of mechanical stimulation, which on the Earth is produced by working against gravity and by our own body weight, is the cause of the loss of bone density in Space (weightlessness - microgravity).
There are two main types of mechanical stimulations which are absent in space.
1) Mechanical stimulation induced by our own body weight. (In a weightless environment, the body has mass but doesn’t have weight.) On the Earth, even in a laying down position, the body gets some amount of mechanical stimulation because the weight of each body particle above provides mechanical stimulation to the below particles. The particles which are below bear the weight of the particles which are above.
2) Mechanical stimulations induced by working against the gravity (against the pull of gravity). Standing, walking, running and jumping are examples of working against the pull of gravity. Actually, by performing any physical activity, the most effort we put in is to support and carry our own body weight.
The most mechanical stimulation induced by working against gravity, like standing, walking, running and jumping, etc, comes from the foot-ground impact forces
There is no foot-ground impact force in a weightless environment (Microgravity). (Hitting the floor with the foot in the Space Station will result in hitting the ceiling with the head.).

Loss of Bone Mass and Bone Mineral Density on Earth (1G Environment)

Insufficient physical activity and/or extreme efficiency in performing locomotion (walking and running) is the cause of the loss of bone mineral density on the Earth. (The competitive marathon runners are affected by the low bone density.)
 
The Biological Basis of Bone MASS and Bone Mineral DENSITY GAIN
 
1)    Excessive (excessive strength and/or excessive duration) mechanical stimulation causes (increased) inflammation of the bones.
 
2)    Sufficient mechanical stimulation (sufficient strength and sufficient duration) maintains normal inflammation (homeostasis).


The Biological Basis of Bone MASS and Bone Mineral DENSITY LOSS
 
1)    Insufficient mechanical stimulation (insufficient strength and/or insufficient duration) causes a decrease in inflammation below the level required for maintaining existing bone mass and bone density. 

MECHANICAL STIMULATION – INFLAMMATION model explains the density loss/gain of all bones, including the bones of the human skull in Space (weightless environment - microgravity) and on the Earth (1 G environment).
1) Bones can increase in size and density. 
2) Bones can increase in size but the bone density decreases
3) Bones can decrease in size and density. 
4) Bone size can decrease, but bone density increases. 

Copyright 2014 – 2021 Luka Tunjic

Luka Tunjic is the author of the book “Mechanical Stimulation Low-Grade Inflammation Weight Gain

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