Lower Limb Stabiltiy and Muscle Action

Question 1

Describe motion when proximal end is fixed and distal end moves. What muscles are involved?

Answer 1

Limb is not weight bearing. Flex at knee. Caused by hamstrings, which are flexor muscles (resisted by gravity)

Question 2

Describe motion when proximal end moves and distal end moves. What muscles are involved?

Answer 2

Limb is weight bearing. Flex a the knee is caused by gravity. Resistance comes from knee extensor (quadriceps)

Question 3

Where is the center of mass of a human located? Where does line of gravity pass through, and where is it going? How does object maintain stability? How would one increase stability?

Answer 3

Anterior to S2.
Passes through center of gravity, aiming towards center of earth (perpendicular to ground)
To maintain stability, line of gravity must stay within supporting base of object. Increase stability by widening support base (using a cane/walker)

Question 4

How do females counter shifting line of gravity during pregnancy?

Answer 4

Arching vertebrae posteriorly, moving line of gravity further into the supporting base of the object

Question 5

Why do objects without muscles/ligament and with joints fall if their line of gravity is outside of the supporting base

Answer 5

Their line of gravity does not pass through the axis of rotation of all their joints.

Question 6

Where does line of gravity pass, relative to the human body

Answer 6

Immediately infront of S2, behind the hip joint, but in front of the knee and way in front of the ankle joints