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Mobile App Chapter 9: Q9-14Q (page 230)
Explain why touching your toes while you are seated on the floor with outstretched legs produces less stress on the lower spinal column than when touching your toes from a standing position. Use a diagram?
Short Answer
When you are seated on the floor with outstretched legs less stress is produced on the lower spinal column than when touching your toes from a standing position. This is because the force required to keep the spine in equilibrium is comparatively high in a standing position.
Step by step solution
Understanding the length of the arm in sitting and standing positions
When a body is in a sitting position, the lever arm for the upper part of the body is smaller as compared to a person standing and bending over.
Explanation for the less stress produced while you are seated on the floor with outstretching legs
Since in a sitting position, relatively small torque is exerted about the hips due to the small length of the lever arm; so, on the upper body, the force of gravity causes small torque resulting in the rotation of the body forward.
Therefore, the force to keep the spine in an equilibrium position is small because the force on the upper half of the body is small.
The following is the diagram showing the sitting position.
In a standing position, the greater length of the arm causes larger torque. Also, the center of mass of the arm is comparatively farther from the support point, which causes more torque.
So, a large force will act to counter the torque that keeps you from collapsing. Therefore, the force to keep the spine in an equilibrium position is larger.
The following is the diagram showing the standing position.
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