Activity 1: Stand with your back and heels against a wall. Now try to bend over as if you were picking something up off the ground just in front of you. What happens and why?
Answer: The further I go down, the more I tend to move forward and lose my balance. As soon as I feel I'm about to fall forward, I put my right foot in front of the other to catch myself from falling. The COG of the body must fall within the base of support (such as the feet) and postural reflexes must exist (like moving a foot forward) so that the total body mass remains balanced. If a person standing leans forward to pick up something from the ground, the pelvis moves rearward to compensate for the forward displacement of the COG of the upper body. But in this example, the wall is preventing the pelvis from making its rearward move. Hence, the body will fall over, unless a foot is placed forward - this will balance the transfer of the COG. Sufficient space around a standing body and room for the feet are therefore needed to avoid loss of balance.
Activity 2: Find a chair and place it with its back against a wall. Lean over the chair and touch your head to the wall - make your back as parallel to the ground as possible. Can you lift the chair and stand up?
Answer: Yes I did, on the first try. It was a medium to heavy-weight chair. Women can do this better than men probably because the COG of a woman's body is lower than that of a man's body. I've read that women have a bigger pelvis area (which allows women to carry a baby when pregnant) thus making her body mass concentrated on the lower portion of her body - as well as her COG. Men on the other hand, have their COG concentrated higher towards the chest area. This therefore makes it harder for them to carry something when their chest is already bent forward.
Activity 3: *I haven't done this because I don't live at my house and therefore don't think I can write on the walls... :)
Answer: The intervertebral discs in our spine have a "viscoelastic" behavior. This means that they deform initially then return rapidly to its original shape when a force is removed - elasticity. They may also become narrow as fluid is expelled and the superior and inferior vertebral bodies move closer together (when compressed), and fluid moves into the disc as the disc space becomes wider (when stretched) - viscosity. These occur as a result of the forces exerted on the spine due to daily normal activities. The shrinkage and expansion of the disc spaces change the measure of a body's stature. This is why some people are taller when they wake up in the morning than when they go to bed at night. According to the book, people are about 1% taller when they wake up and almost 50% of the stature gained is lost in the first half-hour after rising.
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