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

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

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

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

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

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

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)

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

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

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)

Hip angular velocity, moment of force and power during sprinting initial burst of power to create swing latter burst to drive leg down Time (s) Power (W) Moment (N.m) Angular vel. (/s) Toe-off Touch-down Extending Flexing Extensor Flexor Concentric Eccentric

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

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 Time (s) Power (W) Moment (N.m) Angular vel. (/s) Toe-off Touch-down Extending Flexing Extensor Flexor Concentric Eccentric

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

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 Time (s) Power (W) Moment (N.m) Angular vel. (/s) Trial: SL2CF CFS Hit Off Flexing Extending Flexor Extensor Concentric Eccentric

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 Time (s) Power (W) Moment (N.m) Angular vel. (/s) Trial: SL2CF CFS Hit Off Extending Flexing Extensor Flexor Concentric Eccentric

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

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 Time (s) Power (W) Moment (N.m) Angular vel. (/s) Trial: WN02DRMP IFS CTO CFS ITO IFS Dorsiflexing Plantar flexing Dorsiflexor Plantar flexor Concentric Eccentric

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 Time (s) Power (W) Moment (N.m) Angular vel. (/s) Trial: WN02DRMP IFS CTO CFS ITO IFS Extending Flexing Extensor Flexor Concentric Eccentric

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 Time (s) Power (W) Moment (N.m) Angular vel. (/s) Trial: WN02DRMP IFS CTO CFS ITO IFS Flexing Extending Flexor Extensor Concentric Eccentric

Questions? Answers? Thank you.