Week 3 Biomechanical Principles 2

importance of the angle of insertion of a muscle

AoI affects what proportion of the muscle force is at 90 degrees to the axis of rotation, which will actually cause rotation

Mathematical analysis of forces

M = My + Mx

alpha angle

the angle between Mx and M, muscle produces the most force at 90 degrees and the least the endpoints (or 0 degrees), angle of pull of the muscle

resolution

breaking a vector into its component forces

Mx

contributes only translational force to the joint, does not contribute to rotation because is parallel to the axis of rotation

gravity resolution

gravity similarly can be broken down into x and y components, gravity is always straight into the ground, the x component will be parallel to the axis of rotation (in line with the moving bone), and the y component will be 90 degrees from the x component

clinical applications of kinetics

a pt has trouble abducting past 90 degrees when standing because gravity is working at is maximum force potential

how to modify arm position when abducting past 90 degrees to make it easier (using knowledge of levers)

bend the elbow- this will decrease the moment arm and decrease the mechanical advantage of gravity

how to modify arm position when abducting past 90 degrees to make it easier (using knowledge of external load)

lie on back, this will move gravity so that it is not resisting abduction

dynamic analysis

motion analysis: captures position, displacement, velocity, and acceleration, analyzes assess quantity and quality of movement which describes internal and external forces/torques

techniques of dynamic analysis

electrogoniometer, accelerometer, imaging: photo, video, cinematic, optoelectronics; electromagnetic tracking

kinetic measurement examples

mechanical devices like a scale or dynamometer, tranducers like a force plate, electromechanical devices like an isokinetic dynamometer like biodex and kinecom machines