Chapter 9, Problem 14Q

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.

To determine

Explain why touching your toes while you are seated on the floor with outstretched legs produces less stress on the spinal column than when touching your toes from a standing position. Use a diagram.

Answer to Problem 14Q

Solution:

Touching the toes while sitting on the floor with the legs extended produces less tension in the spine than when you touch the toes from a standing position because the lever arm of the upper body is less and therefore the torque made is less. In this way the tension in the spine is less when you are sitting on the floor with your legs extended.

Explanation of Solution

Given info:

Touching your toes while you are seated on the floor with outstretched legs. Touching your toes from a standing position.

Take the pivot at waist height for a person sitting with legs extended (figure on the left). Consider the weight of the upper half of the body doing torque clockwise, for this force the lever arm is relatively small as is the torque made by the arms, therefore the muscles of the back do not do much tension due to the small total torque performed.

For the case of a person touching your toes from a standing position (figure on the right)In the case of a person the lever arm of the upper part of the body and of the arms is greater than in the previous case, therefore the torque performed is much greater and therefore the tension in the spine is greater than in the previous case.

Conclusion:

Touching the toes while sitting on the floor with the legs extended produces less tension in the spine than when you touch the toes from a standing position because the lever arm of the upper body is less and therefore the torque made is less. In this way the tension in the spine is less when you are sitting on the floor with your legs extended.