Determine the joint reaction forces and net muscle moments at the ankle, knee an

Question

Determine the joint reaction forces and net muscle moments at the ankle, knee and hip given the following 2D-coordinates of relevant gait variables in the x-direction and in the y-direction. These coordinates were recorded during stance phase of gait. State all your assumptions. (**Note: the "leg" segment refers to the shank not the entire leg). (**Note: I acts about the CM of the segment) Mass (kg) 1(kgr) 0.011 0.064 0.130 ax (m/s*) -5.33 , (m/s*) Foot Leg Thigh The ankle is at (0.637, 0.063) m, the knee at (0.541, 0.379) m, and the hip at (0.421, 0.708) m. The horizontal GRF is -110 N, the vertical GRF is 720 N, and its center of pressure is (0.677, 0.0) m. (rad/s2) -20.2 -22.4 9.9 C. M. (m) (0.734, 0.089) (0.583, 0.242) (0.473, 0.566) 0.9 2.4 6.0 -0.56 1.01 0.37

Explanation / Answer

Joint reaction force define as the force generated on the joint, response to force acting on the joint.

In the it is result of need to balance the moment arms of the body weight and the muscle.

Joint reaction forces

from Newton, Sum of Horizontal Forces,

from Newton, Sum of Vertical force

Muscle Moment

The moment that we obtain from inverse dynamics tells us which muscle (flexor or extensor) is active, and how much moment (torque) that muscle is exerting. A common standard method of representation of these moments in graphical form, a flexor moment (dorsiflexor at the ankle) is shown as positive, while an extensor (plantarflexor at the ankle) moment is negative.

So the joint reaction force of foot=mass *liner acceleration

=0.9*(-5.33-(1.71))=-8.79

Joint reaction for3ce of leg=2.4*(-1.82-(-0.56))=-3.1

Joint reaction force of thigh=6.0*(1.01-0.37)=3.84

Joint reaction force always higher than body mass.

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