(Summarised content about the bone mass, size, and density from the book “Modern Science of Biomechanics & Weight Gain and Weight Loss”)
Loss of Bone Mineral Density in Space (weightless environment – microgravity)
The absence of mechanical stimulation, which are on the Earth, are produced by working against the gravity and by our own body weight is the cause for the loss of bone density in Space (weightlessness - microgravity).
There are two main types of mechanical stimulations which are absent in space.
1) Mechanical stimulations induced by our own body weight. (In a weightless environment, body has mass but it 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 particle of body which is above provides mechanical stimulation to the particles which are below. The particle which are below bears 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 putt is to support and carry our own body weight.
The most mechanical stimulations induced by working against gravity comes from the ground impact forces. (Hitting the floor with the foot in the Space Station, will result in hitting the ceiling with the head.).
Loss of Bone Mineral Density on the Earth (1G Environment)
Insufficient physical activity and/or extremely efficiency in performing locomotion (walking and running) is the cause for the loss of bone mineral density on the Earth. (The competitive marathon runners are affected with the low bones density.)
the biological basis of bone density
1) Excessive (excessive strength and/or excessive duration) mechanical stimulations cause (increase) inflammation of the bones.
2) Sufficient mechanical stimulation (sufficient strength and sufficient duration) maintains normal inflammation (homeostasis).
3) Insufficient mechanical stimulation (insufficient strength and/or insufficient duration) causes a decrease of inflammation below the level required for maintaining existing bone density and bone volume (bones quality and quantity).
A. “Mechanical Stimulations – Inflammation” model ALONE doesn’t explain the size of the bones.
B. The PHYSIOLOGY of body weight gain and weight loss, explains the size-volume of the bones.
C. On the other hand, the model “Mechanical Stimulation – Inflammation” is the basis for understanding the PHYSIOLOGICAL BASIS of weight gain and weight loss.
Modern Science of Biomechanics explains why: (1) Bones can increase in size and density. (2) Bones can increase in size but the bones density decreases (3) Bones can decrease in size and density. (4) Bone size can decrease but bone density increases. (5) Bones density can increase but the bones strength doesn’t (Increases in bones density doesn’t always cause stronger bones).
The article on my website: “The Mechanism Underlining Excess -Saggy Skin” explains how excessive mechanical stimulation builds and maintains saggy skin.
Click on the following link to see the contents of the book “Modern Science of Biomechanics & Weight Gain and Weight Loss”.