Chapel Garden

PT245 HIP ABDUCTOR MUSCLE FORCE PROBLEM

Page 2

Free Body Diagram

Hip Abductor Muscle Force Picture

The problem can be visualized as two forces (body weight and hip abductor muscle force) and a rigid, horizontal bar or moment arm (the pelvis). The forces are balanced on an axis (the hip joint). These forces and the moment arm comprise a Class I lever system. The diagram is not completely accurate because the direction of the hip abductor muscle force is represented as being vertical. In fact, the hip abductor muscle force is acting at an angle of 70 degrees relative to the horizontal (see skeletal diagram on previous page). To solve the problem, we will need to find the rotary component of the hip abductor muscle force. the rotary component is that part of the hip abductor muscle force that is acting perpendicular to the moment arm (i.e., vertical in this case).

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