Biomechanical Modeling and Analysis of Human Motion

Cole, JoshuaKnapp, Austen

University of Colorado at Colorado Springs, Department of Mechanical Engineering 

Advisor: Prof. Steve Tragesser

The Objective

Create a low cost, non-invasive, portable system for analysis of the internal forces and torques required for human motion

Video CaptureKodak PlaySport

Resolution: 720 X 1280Frame Rate: 60 fps

Image Processing with MATLAB• Manually input initial marker

positions• Filter all colors but green/blue

for each frame• Search based on previous

centroid location• Two colors distinguish between

markers• Output Cartesian Coordinates

Dynamic Modeling

• Modeled body as series of rigid links

• Convert video capture output to angular position

• Two methods of analysis

Point Mass Analysis

Position Data Outputted

Video Capture System

Finite Difference Method

F=ma to attain GRFx & GRFy

• Compute position, velocity, and acceleration of center of mass (CoM) of the three – link model

• Calculate horizontal and vertical components of ground reaction force– Calculated using Newton’s 2nd Law for CoM

Three – Link Analysis

Application of Newton’s 2nd Law and Euler’s Law to attain 9 equation’s of motion (EOM’s)– Three EOM’s per link• 2 EOM’s through • 1 EOM through

Three – Link AnalysisEquations of Motion:

Three – Link Analysis

Angular Position,

Velocity, and Acceleration

EOM’s Internal Forces and Torques

Results and Validation

Point Mass Analysis• GRFy vs. Experimental

Data from Force Plate• Force Plate =

Validation of dynamic analysis

• GRFx << GRFy which is the expected outcome

• Data from 0.0 to ~0.2 seconds is invalid due to filtering of video capture data• Squat performed

after 0.2 sec which allows invalid data to be neglected

Results and Validation

Three-Link Analysis:

• GRFy vs. Experimental Data from Force Plate• GRFy is less accurate

with this model than point mass model

• GRFx increases to a large magnitude which is not correct outcome

• Computations with three-link model more sensitive to measurement errors than point mass analysis

Results and Validation

Three – Link Analysis:• Figure, top to bottom:

• Calculated horizontal component of internal knee force

• Calculated vertical component of internal knee force

• Calculated horizontal component of internal hip force

• Calculated vertical component of internal hip force

• Amplitudes appear to be within a realistic range

Results and Validation

Three – Link Analysis:

Figure 6: Three-Link Calculated Internal Torques

• Ankle, knee, and hip torques• Result of subject’s

muscle actuation• Results qualitatively match

expected torque behavior• Values not consistent

with results in literature

Conclusions and Recommendations

• Partially demonstrated feasibility of system– GRF more accurate than internal forces and

torques• Sources of error–Markers– Clothing Color– Approximations– Frame rate/camera resolution

Future Research and Limitations• Long-term goal: Analyze broad range of human motion

and impact of such motion– Possible through calculation of internal forces and torques– Examples of human motion which could be analyzed:

• Prosthetic patient gait analysis• Sports performance analysis• Low-gravity analysis

• Three-dimensional video capture system• Multi-link model with an arbitrary number of links• Progress EOM’s to allow analysis where feet leave contact

with ground

Thank you

We appreciate you taking your time to listen– Questions/comments/concerns?