Inverse Dynamics Flashcards
What are the fundamental differences between Forward and Inverse Dynamics?
Forward: forces & torques specified, will determine resulting motion
Inverse: determine forces & torque that must act in order to produce given motion
What are the three forces that can be applied, and the three resultant motions?
Direct force > translational motion
Eccentric force > general motion
Force couple > rotational motion
Briefly describe the process of solving a Direct dynamic problem and Inverse dynamic problem
Direct: known forces > equations of motion > double integration > position
Inverse: position > 2nd derivative > equations of motion > known forces
Define inverse dynamics?
process by which forces and torques are indirectly estimated from kinematic and inertial properties of moving bodies
What are the two types of inverse dynamics?
Top-down and bottom-up
Briefly describe the two types of inverse dynamics
Top down: starts from most distal segment, only kinematics and body segmental inertial properties needed
Bottom up: from ground working all the way up to forearm, combines GRF with kinematics and body segmental inertial properties (reduce errors)
Briefly describe the 6 limitations of inverse dynamics
- Forces/moments > mathematical constructs, not actual
- Actual forces in joints/moments across joints are higher (co-contraction of antagonists)
- No certain method to apportion net forces & moments to individual anatomical structures
- Effects of friction & joint structures not considered. Tensions of various ligaments become high near limits of joints, thus moments can occur when muscles are inactive
- When segment isn’t rigid, forces applied to it are attenuated (reduced)
- Sensitivity to input data: joint moment data affected by errors in GRF, CoP, marker locations, segment inertial properties, joint center estimates and segment accelerations.
What is the process of calculating in a inverse dynamics question?
- Breakdown body into kinematic chains
- Breakdown chains into segments
- Assume each segment is “rigid body”
- Assume each joint is rotationally frictionless
- Sketch free body diagram of terminal segment
- Run calculations
Applications: Running & strike pattern. Are peak ankle joint forces higher with rearfoot or forefoot strike?
1.5 BW greater for peak ankle joint forces for forefoot strike. Knee joint also higher (14.4%)
Applications: Tennis Serve. What were the differences between advanced v professional players in terms of joint kinetics and ball velocity?
Martin et al. (2013): 4/16 Parameters were significantly higher for advanced players, shoulder and elbow.
Professional players were more efficient than advanced players, as they maximize ball velocity with lower joint kinetics
Applications: Shoes on running. Are there differences when running in different shoes or barefoot?
Bonacci et al. (2013)
Barefoot running is different to all shod conditions (knee and ankle mechanics)
Suggests minimalist shoe cannot entirely replicate mechanics of running barefoot
Very little difference in running mechanics between shod conditions, other than stride length and frequency (small diff).
Suggests for highly trained runners gait, different shoes have very little impact
Application: What are the differences between young and old adults during gait (walking)?
Same speed and same support torque between groups
Elderly larger contribution from hip extensors, lower contribution from knee extensors, ankle plantar flexors.
Suggests change in motor strategy over life span
Applications: What are the differences between young and old adults during gait (running)?
Decline in running biomechanics over time
Mechanical reductions at ankle (but not hip or knee) correlated with age
Confirms previous observation of biomechanical plasticity, reduced ankle but not hip function in gait (walking application)
