Lifting an object from a forward - leaning position. Consider the biomechanics s

Question

Lifting an object from a forward - leaning position. Consider the biomechanics stress that is sustained within the backbone and muscles of an individual who attempts to lift a weight from a stance in which the body leans forward. A represents the hinge point between the back and hips. B represents a point in the lumbar region of the back. C is the hinge point between upper back and arms (with the shoulder bones intervening). Assume the individual pulls directly upward, from D to C. Theta 1 indicates the amount of forward tilt of the spinal axis. Except for this tilt, an otherwise straight spine is assumed. Theta 2 is the angle between the spinal axis and the line along which a set of lower back muscles exert tension. If the mass to be lifted is 2.5 kg, (a) determine the magnitude of F, the amount of tension supplied by the lumbar muscles. (b) Determine the compressive force on the lowest spinal vertebrae, between A and B. Take AB = 1/4 AC, Theta 1 = 45 degrees and Theta 2 = 8 degrees.

Explanation / Answer

take moment about A
Mg*AC*sin(1)-F*AB*sin(2)=0

F=Mg*AC*sin(1)/(AB*sin(2))=498.423N

compressive force

Fcos(2)=493.57N

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