The three primary bundles of the pectoralis major muscle exert the following for

Question

The three primary bundles of the pectoralis major muscle exert the following forces on the humerus:

F1= 500N @ 30 degrees above the horizontal

F2= 625N @ 5 degrees above the horizontal

F3= 375N @ 20 below the horizontal

Assume the arm is abducted 15 degrees outward from vertical and that the distance from the point of application of these forces to the center of rotation of the shoulder joint (S) is 12cm.

A) What are the individual moments generated by EACH bundle of the pectoralis major about S? (USE CROSS PRODUCTS)

B) What is the net moment generated about S by all 3 muscle forces?

The three primary bundles of the pectoralis major muscle exert the following forces on the humerus:F1= 500N @ 30 degrees above the horizontal F2= 625N @ 5 degrees above the horizontal F3= 375N @ 20 below the horizontal Assume the arm is abducted 15 degrees outward from vertical and that the distance from the point of application of these forces to the center of rotation of the shoulder joint (S) is 12cm. A) What are the individual moments generated by EACH bundle of the pectoralis major about S? (USE CROSS PRODUCTS) What is the net moment generated about S by all 3 muscle forces?

Explanation / Answer

A) moment = r x F

M1 = 500cos30 x 0.12 = 51.96

M2 = 625cos5 x 0.12 = 74.72

M3 = 375 x cos20 x 0.12 = 42.29 in opposite direction of M1 and M2

b) Mnet = M1 +M2 - M3 =84.40

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