Biomedical Engineering Reference
In-Depth Information
Chapter 6
Muscle Force
Incorrect posture adopted daily causes immense forces on the column that are, in
general, responsible for low back pain. The forces that act on the hips during a walk
are very large. Simplified models are used to calculate the magnitude of the
involved forces. The principles that orient these calculations are the conditions
for the static equilibrium of the body or parts of it.
6.1 Objectives
• To establish and to apply the equilibrium conditions of a rigid body
• To find the forces applied on the hips during a walk
• To calculate the forces applied to the spine and to verify the influence of posture
on lifting a heavy object from the floor
6.2 Equilibrium Conditions of a Rigid Body
The equilibrium of a body can be static or dynamic. In this chapter let us discuss the
static equilibrium conditions that must guarantee that neither translation nor rota-
tion of a body occurs. The conditions for equilibrium were already discussed
1. Necessary condition for a body to not undergo translation—the vector sum of all
the forces applied to the body must be zero, that is, the resultant force acting on
the body must be nil:
