When standing on one leg, as is the case during every step (running or walking) the hip abductors must generate enough torque to prevent contralateral pelvic drop. Clinically, weak hip abductors, primarily the gluteus medius and gluteus minimus, can be assessed via Trendelenburg's sign. This can be done by watching the patient walk and/or by asking the patient to balance on one leg and looking for pelvic lean towards the unsupported leg. Below are the beginnings of three free-body diagrams for three different Trendelenburg's test scenarios. 6. Single leg stance with no hand load. a. torque generated by the hip abductors b. force exerted by the hip abductors c. horizontal femoroacetabular joint reaction force d. vertical femoroacetabular joint reaction force e. resultant femoroacetabular joint reaction force magnitude f. resultant femoroacetabular joint reaction force direction relative to the right horizontal FM = ? ?M = 240° relative to the right horizontal Muscle inserts 6 cm directly above the femoroacetabular joint. W = 535 N (minus stance leg) Horizontal distance from CG to femoroacetabular joint is 10 cm.
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Torque generated by the hip abductors: To prevent contralateral pelvic drop, the hip abductors must generate enough torque. Torque is calculated by multiplying the force exerted by the hip abductors by the perpendicular distance from the line of action of the Show more…
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Determine the force exerted by the hip abductor muscles and the joint reaction force at the hip to support the leg and the hip during a single-leg stance. Assume that the abductor muscles make an angle of 70° with the horizontal. Also, assume the person has a mass of 75 kg and that the leg is 16% of the overall mass of the person. (i) Draw and label a free-body diagram of the leg in Figure Q1. (ii) Calculate the hip abductor muscle force. (iii) Calculate the hip joint reaction force. (iv) Calculate the angle the hip joint reaction force makes with the vertical.
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. Leg raises. In a simpli- fied version of the musculature action in leg raises, the abdominal muscles pull on the femur (thigh bone) to raise the leg by pivoting it about one end, as shown in Figure $10.64 .$ When you are lying horizontally, these muscles make an angle of approximately $5^{\circ}$ with the femur, and if you raise your legs, the muscles remain approx- imately horizontal, so the angle $\theta$ increases. We shall assume for simplicity that these muscles attach to the femur in only one place, 10 $\mathrm{cm}$ from the hip joint (although, in reality, the situation is more complicated). For a certain 80 kg person having a leg 90 $\mathrm{cm}$ long, the mass of the leg is 15 $\mathrm{kg}$ and its center of mass is 44 $\mathrm{cm}$ from his hip joint as measured along the leg. If the person raises his leg to $60^{\circ}$ above the horizontal, the angle between the abdominal muscles and his femur would also be about $60^{\circ} .$ (a) With his leg raised to $60^{\circ},$ find the tension in the abdominal muscle on each leg. As usual, begin your solution with a free-body diagram. (b) When is the tension in this muscle greater, when the leg is raised to $60^{\circ}$ or when the person just starts to raise it off the ground? Why? (Try this yourself to check your answer. $(\mathrm{c})$ If the abdominal muscles attached to the femur were perfectly horizontal when a person was lying down, could the person raise his leg? Why or why not?
BIO Leg Raises. In a simplified version of the musculature action in leg raises, the abdominal muscles pull on the femur (thigh bone) to raise the leg by pivoting it about one end (Fig. P11.57. When you are lying. horizontally, these muscles make an angle of approximately $5^{\circ}$ with the femur, and if you raise your legs, the muscles remain approximately horizontal, so the angle $\theta$ increases. We shall assume for simplicity that these muscles attach to the femur in only one place, 10 $\mathrm{cm}$ from the hip joint (although, in reality, the situation is more complicated). For a certain $80-\mathrm{kg}$ person having a leg 90 $\mathrm{cm}$ long, the mass of the leg is 15 $\mathrm{kg}$ and its center of mass is 44 $\mathrm{cm}$ from his hip joint as measured along the leg. If the person raises his leg to $60^{\circ}$ above the horizontal, the angle between the abdominal muscles and his femur would also be about $60^{\circ} .$ (a) With his leg raised to $60^{\circ},$ find the tension in the abdominal muscle on each leg. As usual, begin your solution with a free-body diagram. (b) When is the tension in this muscle greater: when the leg is raised to $60^{\circ}$ or when the person just starts to raise it off the ground? Why? (Try this yourself to check your answer.) (c) If the abdominal muscles attached to the femur were perfectly horizontal when a person was lying down, could the person raise his leg? Why or why not?
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