Question

Problem 3: You want to analyze the forces around the knee joint of your yoga instructor during the Sun Salutation pose (as seen below in A). A) Assume you can model the linkage of the feet with the ground as a fixed constraint acting at a single point. Draw a FBD of the whole body in this position and calculate the reactive components (both force and moment) at the feet during equilibrium. Assume that the z positon of the CG of the instructor is located 10 cm behind the feet (in the negative z-direction), and the the instructor ways 700 N. (2 points) B) Including the information from part A), calculate the muscle tension in the hip flexors and magnitude of the joint reaction force at the hip given the following simplified diagram of the leg. You can assume the leg acts as a single rigid body (ie the knee is locked) and that no other muscles are contributing significantly. The length of the leg is 1m, the center of gravity of the leg is located 0.4 m from the hip joint, and the hip flexor muscle tension makes as 15° angle with the leg with attachments 0.1m below the joint. (5 Points) Hints: Think about what angle the muscle tension makes with the horizontal. Include both components of the ground reaction in your calculations. Do both components of the muscle tension (X and Y) have a non-zero moment arm? Joint F_M Weight of Leg = 100N 75° Ground Reaction from A

          Problem 3: You want to analyze the forces around the knee joint of your yoga instructor during the
Sun Salutation pose (as seen below in A).
A) Assume you can model the linkage of the feet with the ground as a fixed constraint acting at a
single point. Draw a FBD of the whole body in this position and calculate the reactive
components (both force and moment) at the feet during equilibrium. Assume that the z positon of
the CG of the instructor is located 10 cm behind the feet (in the negative z-direction), and the the
instructor ways 700 N. (2 points)
B) Including the information from part A), calculate the muscle tension in the hip flexors and
magnitude of the joint reaction force at the hip given the following simplified diagram of the leg.
You can assume the leg acts as a single rigid body (ie the knee is locked) and that no other
muscles are contributing significantly. The length of the leg is 1m, the center of gravity of the leg
is located 0.4 m from the hip joint, and the hip flexor muscle tension makes as 15° angle with the
leg with attachments 0.1m below the joint. (5 Points)
Hints: Think about what angle the muscle tension makes with the horizontal. Include both components
of the ground reaction in your calculations. Do both components of the muscle tension (X and Y) have a
non-zero moment arm?
Joint
F_M
Weight of Leg = 100N
75°
Ground Reaction from A

Problem 3: You want to analyze the forces around the knee joint of your yoga instructor during the
Sun Salutation pose (as seen below in A).
A) Assume you can model the linkage of the feet with the ground as a fixed constraint acting at a
single point. Draw a FBD of the whole body in this position and calculate the reactive
components (both force and moment) at the feet during equilibrium. Assume that the z positon of
the CG of the instructor is located 10 cm behind the feet (in the negative z-direction), and the the
instructor ways 700 N. (2 points)
B) Including the information from part A), calculate the muscle tension in the hip flexors and
magnitude of the joint reaction force at the hip given the following simplified diagram of the leg.
You can assume the leg acts as a single rigid body (ie the knee is locked) and that no other
muscles are contributing significantly. The length of the leg is 1m, the center of gravity of the leg
is located 0.4 m from the hip joint, and the hip flexor muscle tension makes as 15° angle with the
leg with attachments 0.1m below the joint. (5 Points)
Hints: Think about what angle the muscle tension makes with the horizontal. Include both components
of the ground reaction in your calculations. Do both components of the muscle tension (X and Y) have a
non-zero moment arm?
Joint
FM
Weight of Leg = 100N
75°
Ground Reaction from A

Added by Joy K.

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