Back Exam 1C - Please review and complete the required...

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Unformatted text preview: Please review and complete the required information on this cover page before answering the questions. Biomechanics BMED-4540 Department of Biomedical Engineering Rensselaer Polytechnic Institute In-class closed book exam (Attach Crib Sheet) Date: September 27, 2004 Duration: One hour & 50 minutes (2 PM to 3:50 PM) Total points: 100 Name: gwemé‘ This examination accounts for 20% of your final grade. Please read the instructions carefully and answer each question to the best of your abilities. Total number of pages including cover: 10 NB: Not all ( uestions carr e( ual wei ht. The oints are indicated in arenthesis i) r each question. Allocate your efforts accordingly. Be brief and to the point. 1. Muscle length can remain constant (static contraction), increase (eccentric contraction) or decrease (concentric contraction) during a particular movement of the body. Give one example of each of the three types of muscle contractions. In the examples, clearly indicate the type of movement and the name of the muscle involved (12 points) EXAMPLES Muscle involved oint T e of oint Motion Static contraction: B 1 A... 4 :L Eccentric contraction: 2. a" i, gt. Concentric contraction: Q. 2. The figure below illustrates an athlete doing shoulder muscle strengthening exercises by lowering and raising a barbell with straight arms. In the figure, ‘0’ represents the shoulder joint, ‘A’ is the center of gravity of one arm, and B is a point of intersection of the centerline of the barbell and the extension of line 0A. The distance between 0 and A is 24 cm and the distance between 0 and B is 60 cm. Each arm weighs W-1=50N and the total weight of the barbell is W2=300N. Determine the net moment due to W1 and W2 about the shoulder joint as a function of E), which is the angle the arm makes with the vertical. Calculate the moment for = 45 degrees. (8 points) "‘1. M, w c Wis/me we .3 3. The figure (a) below illustrates a person using an exercise machine. The L—shaped beam shown in figure (b) represents the left arm of the person. Points A and B correspond to the shoulder and elbow joints, respectively. Relative to the person, the upper arm (AB) is extended towards the left (X— direction) and the lower arm (BC) is extended forward (2 direction). At this instant the person is holding a handle that is connected by a cable to a suspending weight. The weight applies an upward (in the y—direction) force with magnitude F on the arm at point C. The lengths of the upper arm and the lower arm are a=25 cm and b=30 cm, respectively, and the magnitude of the applied force is F:200N. Use vector method (cross—product) to determine the magnitudes and direction of moments developed at the lower and upper arms by force F. (12 points) 4, Consider the patella in the knee joint as a movable pulley and. the tendinous attachments to the patella as the two supporting strands (represented by NM and M2 in the figure). If M1 : 500 N, and 81 and 92 equal to 40° and 450., respectively; determine M2 and the magnitude and direction of the joint reaction force (R) at the knee. Ignore the mass of the bones and the body weight. (12 points) 5.. The diagram below shows a dead weight of lOON attached to a patient’s foot by means of a pulley. The distance between the point of knee rotation and the point on the foot where cable is attached is 60 cm (measured along the long axis of the lower leg). The patient uses this set-up while sitting on a chair to exercise her quadriceps muscles. Assume that the weight of the patient’s foot and lower leg is 30N and their combined center of mass is located 20 cm (measured along the long axis of the lower leg) below the knee axis. The tendon of the quadriceps muscles (patellar tendon) inserts in the anterior (front) part of the tibia at 10 cm (measured along the long axis of the lower leg) below the point of knee rotation and the angle of tendon insertion remains at a constant value of 25 degrees (measured clockwise from the long axis of the lower leg) throughout the exercise. What is the magnitude of force necessary for the quadriceps muscles to maintain the exercise load at 0 (position D) and 90 degrees (position A) of flexion? Note that when the knee is at 0 degree of flexion, the pulley rope forms an angle of 19 degrees with the long axis of the leg. (16 points) mwwmm afi1wzw.wmm'mw w m-m.m an sw'd—E'Nil aw mm m in: 3! 55. ; :‘::m1¢r'ma'r<w-mw’mvmm m. . as an M'm .‘m m 6‘ An 890 N man is standing on one foot. Find the magnitude and the direction of the joint reaction force on the head of the supporting femur. The schematic below shows the location and the magnitude of the centers of gravity for the body and the lower leg. “M” is the unknown tension in the hip abductor muscle group (attached at point 0) acting at 71° with the horizontal. Jx and Jy are the unknown x- and y—components of the joint reaction force. (20 points) 7 . State true or false giving reasons. Clearly explain why a given statement is true or false. (20 points) (a) Initiation of human walking involves disturbing the state of equilibrium present in the resting position by the contraction of a number of muscle groups throughout the human body. 3472’ (b) For the loading condition given below in which the weight W is resisted by the tension in quadriceps, the presence of patella in the knee increases the amount of muscle tension in the quadriceps (indicated by M). Q/A'Ze" (c) Knee is a more stable joint than the joint formed between the two vertebrae of spine. Juinl between two vertebrae (d) For surgery requiring replacement of femoral head with a hip implant, shorter stern implants are preferred because they results in less bone marrow loss and, when custom made to a patient”s specification, are as stable as the longer stem implants. 2+2,» (e) The schematic below represents the use of crutches to increase the stability of a person. Determine if the statement below is true or false. Statement: Positions A and B are primarily secure in the anterior-posterior directions While position C is more stable in the frontal plane than in the sagittal plane. 9) l; “e; c? I‘M """n? II..- , bf! 10 ...
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This note was uploaded on 09/07/2008 for the course BMED 4540 taught by Professor Vashishth during the Fall '07 term at Rensselaer Polytechnic Institute.

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Back Exam 1C - Please review and complete the required...

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