BASIC BIOMECHANICS
8th Edition
ISBN: 9781259913877
Author: Hall
Publisher: RENT MCG
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Chapter 4, Problem 10AP
If the anterior and posterior deltoids both insert at an angle of 60° on the humerus and each muscle produces a force of 100 N, how much force is acting perpendicular to the humerus? (Answer: 173.2 N)
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The adjacent diagram displays the joint reaction force between the acetabulum and femoral head for the right leg during single leg stance. Also shown are the abductor muscle force (AMF), the weight of the body above the level of the stance hip (W) and their corresponding moment arms with respect to the joint centre (D and D1). If the right leg weighs 1/6 of total body weight, the ratio of D1 to D is 2.4, and AMF is angled at 30 degrees relative to the vertical, calculate the:
Abductor muscle force (2 marks).
Hip joint reaction force (2 marks).
Express both answers as multiples of total body weight
Explain the answer biomechanically
With the shoulder flexed at 30°, the moment arm of the deltoid muscle is 2.0 cm. Solve
for the force exerted by the deltoid muscle at the glenohumeral joint give the following
assumptions:
The deltoid is the only active muscle at the glenohumeral joint
The weight of the humerus is 48 N.
The center of gravity of the humerus is located 30 cm from the shoulder center of
rotation
STATIC EQUILIBRIUM EQUATIONS
CONSIDERING ONLY THE DELTOID MUSCLE
Fo
MA =
18 Cn
COR
B=55".
0-30°
RaF 30 cm
FG = 24 N
Chapter 4 Solutions
BASIC BIOMECHANICS
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