Investigating The Spine From The Pelvis And Spinae Muscle

The biomechanics problem given had multiple components, and we decided to focus on part B. The objective of part B is to examine the forces acting on the spine from the pelvis and erector spinae muscles as the person pushes the box across the floor. To solve this problem we first had to determine what forces are acting on the spine, and then we needed to know the direction and magnitude of those forces. Since the question asks us to look at the forces acting the spine, we selected the spine to be our system. Next we drew a diagram to visualize all of the forces acting on our system. This diagram can be seen in Figure 1. With this diagram we determined that there are four forces acting on on the spine; force coming from the pelvis (FP), the erector spinae muscle (FM), the shoulder (FS), and the weight of the spine (FW). The arrow that represents the force coming from the pelvis is drawn in any direction because we do not yet know the direction nor magnitude of the force.

Figure 1: Diagram of forces acting on the spinal system

This force was easily determined because it is a value that can be found through research. Assuming that the weight of the spine is 10% of the weight of the human body, we calculated the weight force to be 61 N due to the average weight of the human body being 137 pounds (Walpole et al., 2012). 10% of 137 pounds is 13.7 pounds, and to convert pounds into newtons we multiply by 4.5. This gives us the magnitude of the force. The direction is known because we know that gravity always acts on objects in the negative “y”