Midterm 2 Flashcards
Explain the utility of biochmechanical models in helping understand physiological systems. Provide one example.
- Helping understand the mechanisms underlying a complex biological phenomenon
- Helping estimate a parameter that is difficult to measure
Example: Heart is a pump, bones are rigid bodies
Explain biomechanical indeterminancy. Provide an example of a biomechanically indeterminate problem to help with your explanation. Explain how optimization can be used to solve your specific example.
- BI is when there are more biomechanical variables (forces and moments) that are unknown than there are equations.
- One example is in inverse dynamics analyses where there is more than one muscle acting to generate a moment about the joint. Therefore we could only have 2 FMB equations to solve for 4 unknown moments and forces
- Optimization essentially adds more equations to have as many equations as unknowns. In our example we can assume constant muscle stress which will add 2 more equations therefore yielding the same amount of equations as unknowns.
What is one way to measure center of mass
- use a board supported by scales or force plate at each end and the COM should lie directly above the middle of the board when the scales read the same force
Explain favoured leg design
a favoured leg design is where the required mass is centred closer to the hip. This decreases MOI of the leg about the hip, reducing the moment of force required to swing it for a given angular acceleration and it increases the achievable angular acceleration for a given moment of force
Forward dynamics
Forward dynamics is used to solve for unknown movements (kinematics) that must result given a system model, inertial properties and specification of the forces.
Inverse dynamics
Inverse dynamics are used to solve for unknown forces/moments that must have caused a movement given a system model, inertial properties and measurements of movement.
System identifications
System identification is used to solve for inertial properties that must be present given a system model, specification of the forces and measurements of motion.
What assumptions are u making when you sketch a suitable biomechanical model
- segments are rigid bodies
- All joints are pin joints (1 rotational degree of freedom per joint)
- drawn in 2D
How do we determine the required inertial properties
Knowing subjects height and mass we can use anthropometric tables to look up estimates of segment inertial properties
What is a pure moment
a pure moment is a collection of forces that have a resultant moment but no resultant force. they have rotational action but no translational action
Why can’t vertical ground reaction forces exert pure moments on a person’s foot?
Typically vertical ground reaction forces can’t exert a pure moment because they can’t pull down on the foot. This means that the resultant grf can never have a resultant force = 0 while having a non zero moment
what measurement tools are you going to need when using inverse dynamics to calculate the knee joint
- force plates to measure ground reaction forces
- motion capture to measure segment linear and rotational acceleration
Forward dynamics (nervous system)
Known forces from muscles and known inertial properties from internal model to predict our movement
Inverse dynamics (nervous system)
The known movement from what we want to achieve and the known inertial properties from the internal model to estimate our forces
System identification (nervous system)
Applying known forces and movements to our system to find inertial properties
