When picking up an object from the ground, it is generally recommended that you "lift with your legs" - that is, raise and lower yourself by bending your knees but keeping your upper body upright. If instead, you "lift with your back" by bending at the hip so that your upper body is angled, then you put a great deal more stress on your spine and back muscles. Consider a person who is "lifting with their back" such that they are bent at the hip with their upper body is parallel to the ground (i.e., their spine is oriented horizontally). Let us calculate the tension in the back muscles and the compression on the spine in this situation. We will model the spine and upper body as a horizontal rigid rod or uniform density with a length of 50.0 cm and a mass of 40.0 kg. Assume that the person attempts to lift an object with their arms, which we will model as attached at the far end of the rod. Support of the back in this position is provided primarily by the erector spinalis muscle which we will model as being attached at one end to the spine at a point 33.0 cm from the hip at an angle of 10 degrees; the other end of the muscle is attached to the lower body below the hip.
When picking up an object from the ground, it is generally recommended that you "lift with your legs" - that is, raise and lower yourself by bending your knees but keeping your upper body upright. If instead, you "lift with your back" by bending at the hip so that your upper body is angled, then you put a great deal more stress on your spine and back muscles. Consider a person who is "lifting with their back" such that they are bent at the hip with their upper body is parallel to the ground (i.e., their spine is oriented horizontally). Let us calculate the tension in the back muscles and the compression on the spine in this situation. We will model the spine and upper body as a horizontal rigid rod or uniform density with a length of 50.0 cm and a mass of 40.0 kg. Assume that the person attempts to lift an object with their arms, which we will model as attached at the far end of the rod. Support of the back in this position is provided primarily by the erector spinalis muscle which we will model as being attached at one end to the spine at a point 33.0 cm from the hip at an angle of 10 degrees; the other end of the muscle is attached to the lower body below the hip.
University Physics Volume 1
18th Edition
ISBN:9781938168277
Author:William Moebs, Samuel J. Ling, Jeff Sanny
Publisher:William Moebs, Samuel J. Ling, Jeff Sanny
Chapter12: Static Equilibrium And Elasticity
Section: Chapter Questions
Problem 34P: In order to get his car out of the mud, a man ties one end of a rope to the front bumper and the...
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University Physics Volume 1
Physics
ISBN:
9781938168277
Author:
William Moebs, Samuel J. Ling, Jeff Sanny
Publisher:
OpenStax - Rice University