Kinetics versus Kinematics for Analyzing Locomotor Coordination

1. Kinetics versus Kinematics for Analyzing Locomotor Coordination D. Gordon E. Robertson, Ph.D. School of Human Kinetics, University of Ottawa, Ottawa, CANADA

2. Kinematic Analysis • linear position, velocity and acceleration of markers • linear position, velocity and acceleration of body segments • angular position, velocity and acceleration of body segments • total body or limb kinematics

3. Advantages of Kinematics • easy to obtain with automated motion analysis systems • accuracy is easy to determine • requires little operator expertise • immediate feedback possible

4. Disadvantages of Kinematics • only describes motion • not indicative of causes • difficult to discriminate important variables from idiosyncratic variables

5. Kinetic Analysis • forces and moments of force • work, energy and power • impulse and momentum • inverse dynamics derives forces and moments from kinematics and body segment parameters

6. Advantages of Kinetics • defines which structures cause the motion (i.e., coordination) • can be used to simulate motion and describe resulting kinematics • can be validated against external force measurements

7. Disadvantages of Kinetics • may require synchronization of several data acquisition systems (e.g., videography with force plates) • special training to interpret • more expensive and less developed software • invasive for direct internal measurements (muscle, ligament, or bone forces)

8. Inverse Dynamics is Partial Solution to Invasive Measurements • noninvasive with videography • kinematics are determined • direct measurements of external forces are often necessary (i.e., force platforms) • can be applied at several joints, simultaneously

9. Limitations of Inverse Dynamics • results apply to conceptual structures not true anatomical structures • cannot partition results into contributions by individual anatomical structures • no direct means of validating • modeling permits partitioning of forces and moments

10. Sprint Analysis Example • swing phase of one leg • world-class male sprinter • 50 m into 100 m competitive race (t=10.06 s) • analysis of hip and knee only (ankle forces not significant during swing)

11. Hip angular velocity, moment of force and power during sprinting • initial burst of power to create swing • latter burst to drive leg down 20. Flexing 0. Extending -20. 300. Flexor 0. Power (W) Moment (N.m) Angular vel. (/s) Extensor -300. Concentric 2000. 0. Eccentric -2000. Toe-off Touch-down -4000. 0.0 0.1 0.2 0.3 0.4 Time (s)

12. Hip Moment • causes rapid hip and knee flexion immediately after toe-off • causes hip and knee to extend in preparation for touch-down

13. Knee angular velocity, moment of force and power during sprinting • initial burst of power to stop flexion • small burst for extension • final burst to stop extension 20. Extending 0. -20. Flexing 300. Extensor 0. Power (W) Moment (N.m) Angular vel. (/s) -300. Flexor 2000. Concentric 0. -2000. Eccentric Toe-off Touch-down -4000. 0.0 0.1 0.2 0.3 0.4 Time (s)

14. Knee Moment • not used to cause flexion or extension during swing • stops knee flexion before mid-swing • prevents hyper-extension (locking) prior to touch-down

15. Hip angular velocity, moment of force and power during kicking • initial burst of power to create swing • negative work to create whip-action of leg and foot 20. Flexing 0. -20. Trial: SL2CF Extending 200. Flexor 0. Power (W) Moment (N.m) Angular vel. (/s) -200. Extensor Concentric 1000. 0. -1000. Eccentric CFS Hit Off -2000. 0.0 0.1 0.2 0.3 Time (s)

16. Knee angular velocity, moment of force and power during kicking • initial power to stop flexion, bumper effect • negative power prior to contact to prevent hyperextension 20. Extending 0. -20. Trial: SL2CF Flexing 200. Extensor 0. -200. Power (W) Moment (N.m) Angular vel. (/s) Flexor Concentric 1000. 0. -1000. Eccentric CFS Hit Off -2000. 0.0 0.1 0.2 0.3 Time (s)

17. Normal Walking Example • athletic male subject • laboratory setting • speed was 1.75 m/s • IFS=ipsilateral foot-strike • ITO=ipsilateral toe-off • CFS=contralateral foot-strike • CTO=contralateral toe-off

18. Ankle angular velocity, moment of force and power during walking • large burst of power by plantar flexors for push-off • dorsiflexors allow gentle landing and flexion during swing 10. Dorsiflexing 0. -10. Trial: WN02DRMP Plantar flexing 100. Dorsiflexor 0. Power (W) Moment (N.m) Angular vel. (/s) -100. Plantar flexor 250. Concentric 0. -250. -500. Eccentric IFS CTO CFS ITO IFS -750. 0.0 0.2 0.4 0.6 0.8 1.0 Time (s)

19. Knee angular velocity, moment of force and power during walking • initial burst of power to cushion landing • positive work to extend knee • negative work by extensors to control flexion at push-off 10. Extending 0. -10. Trial: WN02DRMP Flexing 100. Extensor 0. -100. Power (W) Moment (N.m) Angular vel. (/s) Flexor 250. Concentric 0. -250. -500. Eccentric IFS CTO CFS ITO IFS -750. 0.0 0.2 0.4 0.6 0.8 1.0 Time (s)

20. Hip angular velocity, moment of force and power during walking • some cushioning at landing • large amount of negative work by flexors • positive work by flexors to swing leg 10. Flexing 0. -10. Trial: WN02DRMP Extending 100. Flexor 0. -100. Power (W) Moment (N.m) Angular vel. (/s) Extensor 250. Concentric 0. -250. -500. Eccentric IFS CTO CFS ITO IFS -750. 0.0 0.2 0.4 0.6 0.8 1.0 Time (s)

21. Questions? Answers? Thank you.