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D. Gordon E. Robertson, PhD Fellow, Canadian Society for Biomechanics Emeritus Professor, University of Ottawa.

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Presentation on theme: "D. Gordon E. Robertson, PhD Fellow, Canadian Society for Biomechanics Emeritus Professor, University of Ottawa."— Presentation transcript:

1 D. Gordon E. Robertson, PhD Fellow, Canadian Society for Biomechanics Emeritus Professor, University of Ottawa

2 Study of forces and their effects on living bodies Types of forces External forces ground reaction forces applied to other objects or persons fluid forces (swimming, air resistance) impact forces Internal forces muscle forces (strength and power) force in bones, ligaments, cartilage

3 Temporal Kinematic Kinetic Direct Indirect Electromyographic Modeling/Simulation

4 Quantifies durations of performances in whole (race times) or in part (splits, stride times, stroke rates, etc.) Instruments include: stop watches, electronic timers timing gates frame-by-frame video analysis Easy to do but not very illuminating Necessary to enable kinematic studies

5 Donovan Bailey sets world record (9.835) despite slowest reaction time (0.174) of finalists Reaction timesRace times

6 Position, velocity (speed) & acceleration Angular position, velocity & acceleration Distance travelled via tape measures, electronic sensors, trundle wheel Linear displacements point-to-point linear distance and direction Angular displacements changes in angular orientations from point-to- point using a specified system (Euler angles, Cardan angles etc.). Order specific.

7 Instrumentation includes: tape measures, electrogoniometers speed guns, accelerometers motion capture from video or other imaging devices (cinefilm, TV, infrared, ultrasonic, etc.) GPS, gyroscopes, wireless sensors

8 Cheap to very expensive Cheap yields low information e.g., stride length, range of motion, distance jumped or speed of object thrown or batted Expensive yields over-abundance of data e.g., marker trajectories and their kinematics, segment, joint, and total body linear and angular kinematics, in 1, 2, or 3 dimensions and multiple angular conventions Are essential for later inverse dynamics and other kinetic analyses

9 Stride velocity = stride length / stride time Stride rate = 1 / stride time Notice that running foot- prints are typically on the midline unlike walking when they are on either side

10 Hip locations of last 60 metres of 100-m race Male 10.03 s accelerated to 60 m before maximum speed of 12 m/s Female 11.06 s accelerated to 70 m before maximum speed of 10 m/s Both did NOT decelerate!

11 Direct measures such as electrogoniometry (for joint angles) or accelerometry are relatively inexpensive but can yield real-time information of selected parts of the body Accelerometry is particularly useful for evaluating impacts to the body headform with 9 linear accelerometers to quantify 3D acceleration Inside headform (below) is a 3D accelerometer and 3 pairs of linear sensors for 3D angular acceleration

12 Multiple infrared cameras or infrared markers Motion capture system Usually multiple force platforms Subject has 42 reflective markers for 3D tracking of all major body segments and joints

13 X, Y, Z linear velocities of stick head Forward and vertical velocities of centre of gravity

14 Sagittal, transverse, and axial rotational velocities of L5/S1 and hip joints

15 Forces or moments of force (torques) Impulse and momentum (linear and angular) Mechanical energy (potential and kinetic) Work (of forces and moments) Power (of forces and moments)

16 Two ways of obtaining kinetics Direct dynamometry Use of instruments to directly measure external and even internal forces Indirect dynamometry via inverse dynamics Indirectly estimate internal forces and moments of force from directly measured kinematics, body segment parameters and externally measured forces Instron compression tester for force and deformation measures of bones, muscles, ligaments, etc., under load Gait laboratory (U. of Sydney) with 10 Motion Analysis cameras and walkway with five force platforms

17 Measurement of force, moment of force, or power Instrumentation includes: Force transducers strain gauge, LVDTs, piezoelectric, piezoresistive Pressure mapping sensors Force platforms strain gauge, piezoelectric, Hall effect Isokinetic for single joint moments and powers, concentric, eccentric, isotonic

18 Strain gauge: inexpensive, range of sizes, and applications dynamic range is limited, has static capability, easy to calibrate can be incorporated into sports equipment Examples: bicycle pedals, oars and paddles, rackets, hockey sticks, and bats

19 Subject used a Gjessing rowing ergometer with a strain gauge force transducer on cable that rotates a flywheel having a 3 kilopond resistance Force tracing visible in real-time to coach and athlete Increased impulse means better performance Applies to cycling, canoeing, swim or track starts

20 Pressure mapping sensors: moderately expensive, range of sizes and applications, poor dynamic response can be incorporated between person and sport environment (ground, implement) Examples: shoe insoles, seating, gloves

21 Piezoelectric: inexpensive, range of size and application poor static capability, difficult to calibrate suitable for laboratory testing or in sports arenas Examples: load cells, force platforms

22 Helmet and 5-kg headform dropped from fixed height onto an anvil. Piezoresistive force transducer in anvil measures linear impact (impulse) and especially peak force Peak force is reduced when impulse is spread over time or over larger area by helmet and liner materials

23 Typically measure three components of ground reaction force, location of force application (called centre of pressure), and the free (vertical) moment of force Piezoelectric: expensive, wide force range, high dynamic response, poor static response Strain gauge: moderately expensive, narrow force range, moderate dynamic response, excellent statically

24 Instantaneous ground reaction force vectors are located at the centres of pressure Force signatures show pattern of ground reaction forces on each force platform

25 process by which all forces and moments of force across a joint are reduced to a single net force and moment of force the net force is primarily caused by remote actions such as ground reaction forces or impact forces the net moment of force, also called net torque, is primarily caused by the muscles crossing the joint thus it is highly related to the coordination of the motion, injury mechanisms and performance free body diagram with actual muscle forces, ligament forces, bone-on-bone forces and joint moment of force joint kinetics are simplified as a single force and a moment of force (in blue)

26 requires linear and angular kinematics of the segments and knowledge of the segments inertial properties inertial properties are usually obtained by using proportions to estimate the segments mass and then equations based on the mass being equally distributed in a representative geometrical solid (e.g., ellipsoid, frustum of a cone, or elliptical cylinder) based on the segments markers head is an ellipsoid, trunk and pelvis are elliptical cylinders, other segments are frusta of cones

27 generally analyses start with a distal segment what is either free swinging or in contact with a force platform or force transducer then the next segment in the kinematic chain is analyzed process continues to the trunk and then starts again at another limb

28 Net forces add no work nor do they dissipate energy then can: transfer energy from one segment to another passively Net moments of force can: generate energy by doing positive work at a joint dissipate energy by doing negative work across a joint transfer energy across a joint actively (meaning that muscles are actively recruited unless joint is fully extended or flexed)

29 Power of the net force is: P force = F · v Power of net moment of force is: P moment = M · Work done by net moment of force is computed by integrating the moment power over time W moment P moment dt Work done by net force is zero

30 male sprinter (10.03 s 100-m) at 50 m into race stride length approximately 4.68 metres horizontal velocity of foot in mid-swing was 23.5 m/s (84.6 km/h)! only swing phase could be analyzed since no force platform in track

31 knee extensor moment did negative work (red) during first half of swing (likely not muscles) knee flexors did negative work (blue) during second half to prevent full extension (likely due to hamstrings) little or no work (green) done by knee moments angular velocity moment of force moment power swing phase

32 hip flexor moment did positive work (red) during first part of swing (rectus femoris, iliopsoas) hip extensor moment did negative work mid-swing (green) then positive work (blue) for extension (likely gluteals)

33 knee flexors (rectus femoris and iliopsoas) are NOT responsible for knee flexion during mid-swing hip flexors are responsible for both hip flexion AND knee flexion during swing hip flexors are most important for improving stride length hip extensors (gluteals) are necessary for leg extension while knee flexors (hamstrings) prevent knee locking before landing

34 foot lifts at green arrow, impact at red arrow foot velocity at impact was 8.6 m/s (31 km/h) knee extensors do no work, knee flexors (red) instead do negative work to prevent hyperextension hip flexors do positive work (green) then extensors do negative work (blue) to create whip action -2000 -1500 -1000 -500 0 500 1000 1500 2000 Time (s) Knee power Hip power

35 Benefits: can attribute specific muscle groups to the total work done within the body can exhibit coordination of motion Drawbacks: net moments are mathematical constructs, not measures physiological structures cannot validate with direct measurements cannot detect elastic storage and return of energy cannot quantify multi-joint transfers (biarticular muscles)

36 process of measuring the electrical discharges due to active muscle recruitment only quantifies the active component of muscle, passive component is not recorded levels are relative to a particular muscle and particular person therefore need method to compare muscle/muscle or person/person not all subjects can perform maximal voluntary contractions (MVCs) to permit normalization effective way to identify muscle is recruitment

37 Types: cable reliable less expensive encumbers subject cable telemetry reliable less expensive less cabling telemetry unreliable more expensive no cabling

38 Types: surface (best for sports) reliable less expensive noninvasive fine wire unreliable more expensive invasive needle (best for medical) unreliable more expensive painful

39 experience male lacrosse player release velocity 20 m/s (72 km/h) duration from backswing to release 0.45 s hybrid style throw 8 surface EMGs of (L/R erector spinae, L/R external obliques, L/R rectus abdominus, and L/R internal obliques) four force platforms maximum speed throws into a canvas curtain

40 left erector spinae right erector spinae left external obliques right external obliques left rectus abdominus right rectus abdominus left internal obliques right internal obliques start of throwrelease erector spinae quiet at release ext. obliques highly active rect. abd. only on near release noticeable left/ right asymmetry

41 Benefits identifies whether a particular muscle is active or inactive can help to identify pre-fatigue and fatigue states Drawbacks encumbers the subject difficult to interpret cannot identify what contribution muscle is making (concentric, eccentric, isometric) should be recorded with kinematics

42 musculoskeletal models measure internal muscle, ligament and bone-on-bone forces difficult to construct, validate, and apply forward dynamics predicts kinematics based on the recruitment pattern of muscle forces difficult to construct, validate, and apply computer simulations requires appropriate model (see above) and accurate input data to drive the model can help to test new techniques without injury risk

43 kinematics are useful for distinguishing one technique from another, one trial from another, one athlete from another kinematics yields unreliable information about how to produce a motion direct kinetics are useful as feedback to quickly monitor and improve performance direct kinetics does not quantify which muscles or coordination pattern produced the motion

44 inverse dynamics and joint power analysis identifies which muscle groups and coordination pattern produces a motion cannot directly identify specific muscles, biarticular contractions, or elasticity electromyograms yield level of specific muscle recruitment and potentially fatigue state electromyograms are relative measures of activity and cannot quantify passive muscle force, should be used with other measures

45 School of Human Kinetics, University of Ottawa, Ottawa, Ontario Canadian beaver in winter, Gatineau Park, Gatineau, Quebec

46 Muchas Gracias

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