Deck 4: Calculating the Loads on the Body

Question 1

When using a kinetic link model for planar inverse dynamics, we must make several assumptions regarding the model. Which of the following assumptions also allows the researcher to assume the mass moment of inertia, length and centre of mass of each segment remains constant throughout a movement?

A) Each joint is a rotationally frictionless pin or hinge joint.
B) Joint forces and moments are equal and opposite about a joint.
C) Air friction is minimal.
D) Each segment is a rigid body with its mass concentrated at the centre of mass.

Answer 1

D

Question 2

A model will generally include several types of forces. Which type of force acts downward through the centre of mass of each segment and has an acceleration of 9.81m/s2?

A) Muscle force
B) Gravitational force
C) Net muscle force
D) Ground reaction force

Answer 2

B

Question 3

In a two-dimensional or planar analysis a segment or object has three degrees of freedom, two translational degrees (horizontal and vertical) and one rotational degree (orthogonal to the translational plane) Thus how many equations of motion may be written for each segment in the kinetic chain?

A) 2
B) 4
C) 3
D) 6

Answer 3

C

Question 4

Unfortunately, because we have many muscles acting on a joint or segment we often end up with more than three unknowns. When you have more unknowns then equations to solve them you face the problem called __________.

A) redundancy
B) indeterminacy
C) unquantifiable
D) uncertainty

Question 5

Which of the following is not a known method of solving the indeterminacy problem?

A) calculating joint reaction forces
B) measuring muscle forces directly
C) reduction optimisation
D) reverse optimisation

Question 6

The moment of a force about a point, acts in a direction that is orthogonal to the plane defined by the point of rotation (O), the point of application of force (P) and the force vector (F; Figure 4.2(b)in the text) How do we specify the direction of a moment?

A) Left hand rule
B) Right thumb rule
C) Right hand rule
D) Orthogonal rule

Question 7

When studying planar dynamics it is easiest to begin with a static example because the system is in equilibrium. In this context what does equilibrium mean?

A) The system may be travelling at a constant linear and rotational velocity.
B) Both a and c are correct.
C) The state in which the sum of the forces and the sum of the moments acting on the system are zero.
D) The segment will have no muscle forces acting on it.

Question 8

What is an inertial reference frame?

A) A frame of reference that is accelerating.
B) A heavy frame of reference.
C) A frame of reference that is not accelerating.
D) A frame of reference that is stationary.

Question 9

principle of moments, states that the moment of a force about a point is equal to the sum of the moments of the force's components about a point. This principle is also known as...

A) Varignon's theorem.
B) Newton's law
C) Varignon's law
D) principle component theorem

Question 10

A free-body diagram (Figure 4.3(b) in the text) shows the biomechanical system of interest, here the forearm-hand segment, isolated from the surrounding world. Forces acting on the segment are: the weight of the forearm and hand (Fg = m g) at their centre of mass, the muscle force (Fm) and the x- and y-components of the joint force (Fjx, Fjy), producing the three force equations of 4.1. Values that are known are as follows: m = 1.5 kg, r = 0.14 m, rm = 0.05 m and φ = 80Ëš. What is the value of Fjx?

A) 9.69 N
B) 7.15 N
C) 55.8 N
D) 40.57 N

Question 11

Using the joint reaction force simplifies our analysis because it is derived from the net force that is transmitted from one segment to the other. Which of the following statements regarding joint reaction force is incorrect?

A) We cannot tell from the net forces and moments how the load is shared between the various internal structures of the segment.
B) The net force may represent many different forces, such as muscles, ligaments and bone-on-bone contacts.
C) This approach does not allow the direct calculation of the actual forces acting on joints and bones and within muscles and other soft tissues.
D) Joint reaction force as such is a real occurrence and can be directly measured.

Question 12

There are many methods for overcoming the indeterminacy problem. In this method the number of unknowns is reduced by grouping muscles with similar functions or muscles with common anatomical insertion points and eliminating muscles that are considered to be inactive. Which method is this?

A) Inverse Optimisation.
B) Reduction Method.
C) Direct measurement method.
D) Muscle Energy Method.

Question 13

Inverse optimisation uses mathematical optimisation techniques of cost functions and constraint equations to resolve resultant joint moments into individual muscle forces in musculoskeletal models. Which type of cost function uses sum of muscle forces or sum of muscle stresses?

A) Minimum fatigue criterion.
B) Muscle energy technique.
C) Dynamic modelling.
D) Linear functions.

Question 14

When conducting an analysis of a multi-segment chain, which segment do we typically begin the process with when force plate data is available?

A) Most distal.
B) Most proximal.
C) The head.
D) The shoulder.

Question 15

One of the assumptions of linear inverse dynamics is that the body being studied is a series of rigid segments. However, we can see from high-speed recordings of impacts, the soft parts of each segment of the human body are shifted relative to the bony parts and start to 'wobble' in a complex damped manner. Modelling the body based on the concept of wobble is called what?

A) Varignon's theorem.
B) Dynamic modelling.
C) Wobbling mass model.
D) Inverse dynamics.