Assess the strength of human tissues and their margins of safety when exercise i

Question

Assess the strength of human tissues and their margins of safety when exercise i.e. the tension in the Achilles tendon in our foot when we walk and when we jump. Consider bone structure of the foot and equilibrium of forces. To calculate the tension in the Achilles tendon consider the joint between the tibia and talus bones as a pivot From Thermann et aI., the average cross sectional area of the Achilles tendon is 127mm2 The ultimate strength of Achilles tendon is approximately 55 MPa in the 10 to 29 years age group. (According to Yamada, H. (1970) Strength of Biological Materials. Williams and Wilkins. Baltimore (translated by F. G. Evans).

Explanation / Answer

weight of the body=W
considering the body weight to be distributed equally in both the legs ,
the weight to be balanced by one foot=W/2

moreover to prevent the dislocation of joint,
Tx1.5"=Fx6"
T=4F----------------------------(1)
and T+F=W/2 (both the forces=half the body weight)
substituting value from (1)

4F+F=W/2
F=W/10
T=4W/10

now strength=tension/cross sectional area
55MPa=T/127mm2

maximum T =55x106 x127x10-6 N

T=6985N

maximum F=1746.25N

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