Biomechanics 10/10/22: Motion Analysis
Kinematics: Study of bodies in motion without regard to the causes of motion (position,
velocity or acceleration).
o It is concerned with the describing and quantifying both the linear and angular
positions of bodies and their time derivatives
Imaging/Motion Capture Systems are used to record the motion of markers affixed to a
moving subject, followed by manual or automatic digitizing to obtain the co-ordinates of the
markers
Quintic/SIMI Motion Analysis:
o Simple biomechanical measures both qualitatively and quantitatively
o Manual digitisation and automated digitisation (limited to 2D actions in Quintic/3D
in SIMI)
OptoElectronic Motion Analysis Theory
o Series of cameras which project infra-red light onto reflective spheres/targets
o Reflected light is optically registered by the cameras
o Process automatically registers the location of the targets in space, less time
consuming than traditional methods
Cameras work up to 1000-2000Hz
o Host computer takes the images from the cameras and reconstructs the data
Each marker must be visible by 2 cameras at all times
o Problems occur due to loose fitting clothing/long hair – misidentification, cross-over
of targets, target drop out
o Tester interventions required to rectify these problems
Calibration: ensuring the image coordinates are correctly scaled to size
o Control points attached to a calibration wand of dimensions
o 2D analysis: at least four noncollinear points
o 3D analysis: at least 6 noncollinear points
o Possible to obtain reconstruction accuracies less then 1mm
o Equations are computed to scale the coordinates into real metric units
o Compare actual coordinate locations of the control points with their refined
coordinated
o Standard error or root mean square of the differences between the true co-ordinate
locations and their digitized and refined location represents the accuracy of the
system
Kinematics: Study of bodies in motion without regard to the causes of motion (position,
velocity or acceleration).
o It is concerned with the describing and quantifying both the linear and angular
positions of bodies and their time derivatives
Imaging/Motion Capture Systems are used to record the motion of markers affixed to a
moving subject, followed by manual or automatic digitizing to obtain the co-ordinates of the
markers
Quintic/SIMI Motion Analysis:
o Simple biomechanical measures both qualitatively and quantitatively
o Manual digitisation and automated digitisation (limited to 2D actions in Quintic/3D
in SIMI)
OptoElectronic Motion Analysis Theory
o Series of cameras which project infra-red light onto reflective spheres/targets
o Reflected light is optically registered by the cameras
o Process automatically registers the location of the targets in space, less time
consuming than traditional methods
Cameras work up to 1000-2000Hz
o Host computer takes the images from the cameras and reconstructs the data
Each marker must be visible by 2 cameras at all times
o Problems occur due to loose fitting clothing/long hair – misidentification, cross-over
of targets, target drop out
o Tester interventions required to rectify these problems
Calibration: ensuring the image coordinates are correctly scaled to size
o Control points attached to a calibration wand of dimensions
o 2D analysis: at least four noncollinear points
o 3D analysis: at least 6 noncollinear points
o Possible to obtain reconstruction accuracies less then 1mm
o Equations are computed to scale the coordinates into real metric units
o Compare actual coordinate locations of the control points with their refined
coordinated
o Standard error or root mean square of the differences between the true co-ordinate
locations and their digitized and refined location represents the accuracy of the
system
