Mechanics of human movement. Structures implied in movement. Kinematic conventions. Necessary to analyze human motion

Transcription

1 Mechanics of human movement M. Foidart-Dessalle (Prof. FM, ULg) S. Cescotto (Prof. FSA, ULg) F. Pascon (FNRS) 1 Structures implied in movement Bones and Joints: Moving Structures Motor forces: Gravity, muscle contractions, friction forces, ground reaction, aquatic,. 2 Kinematic conventions Necessary to analyze human motion Kinematics (descriptive analysis) displacement, velocity, acceleration Kinetics (causal analysis) forces 3 1

2 LES CHAINONS OSSEUX 4 Schematic representation of joints Joints (rotation centers) are represented as points It is a necessary approximation Rotation centers are between 18.9 (scapula) and 12 (elbow) square mm 5 6 2

3 7 Schematic model of human body Segments joining points: mechanical axis # of anatomic axis Either all body, either part of it: limb, part of it 8 9 3

4 Kinematics Position = localization in space Global reference frame needed Use a human reference frame Movements wrt the human reference frame Relative movements of the limbs 10 «Human reference frame» 3 reference planes 11 Examples of movements that could be described wrt the human reference frame 12 4

5 Examples of relative movements between limbs Classification of diarthroses with concordant surface 15 5

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7 Kinematic analysis: : position/time time 19 Numeric and graphic analysis For complex movements velocity and acceleration can be calculated from position-time time data obtained with high precision cameras and chronometers 20 Graphic resolution 21 7

8 Graphic resolution Measurement techniques Historical: Chronophotography running man 24 8

9 Measurement techniques Historical: Chronophotography walking man 25 Measurement techniques Historical: Chronophotography 26 Measurements techniques Stroboscopic flash 27 9

10 Measurement techniques Electrogoniometry 28 camera platform for force measurement Measurement techniques 29 Electrodes inside the muscles for precise measurements of muscle activity 30 10

11 Electrodes on the muscle for simple measurements of muscle activity Reflecting spheres to capture the movement by 5 cameras 3D and numerical walk hip curve and numerical walk 31 Anthropometric requirements Length of the segments Weight and density of whole body and segments The center of mass location Moment of inertia and radius of giration 32 Length of segments Necessary determination to represent the body and its segments at the right scale Direct measure is preferable Data from tables give length of segments as fractions of whole body height 33 11

12 34 Whole body density Useful in determination of mass centers and moments of inertia In the past it was measured on cadavers/ then on segments volumes with tables / nowadays on cross-sections sections obtained by scanning the segments at regular intervals 35 Determination of mass centers and moments of inertia Measurements with tables Direct measurements with accelerometers: quick release experiment 36 12

13 Whole body density Density of the whole body depends on respective density of bone (>1.8), muscle ( 1), fat (<1) Ponderous index in metric units c = h/w : kg/m Whole body density d = c 37 Segment densities

14 Segments weight ratios Upper body part / Lower body part: 5/3 Head and trunk / both upper limbs: 4/1 Head / trunk: 1/6 Arm / forearm and hand: 1/1 Hand / Forearm: 1/3 Thigh / leg and foot: 5/3 Leg / foot: 3/1 40 Muscles anthropometric data Physiological Cross sectional Area (PCA) of a muscle is a measure of the numbers of sarcomers (contractile units) parallel to the angle of pull of the muscle. In pennate muscles, only the parallel component in effective. PCA = m cos θ / D l θ = pennation angle m = mass D = density l = length Force/unit cross section area ranges from 0.20 to 1MPa (0.70 MPa in quadriceps during running and jumping) 41 Physiological Cross-section Area of some muscles Muscle Mass Fiber length PCA Pennation angle Sartorius 75 g 38 cm 1.9 cm² 0 Biceps femoris 150 g 9 cm 15.8 cm² 0 Semitendinosus 75 g 16 cm 4.4 cm² 0 Soleus 215 g 3.0 cm 58 cm² 30 deg Gastrocnemius 158 g 4.8 cm 30 cm² 15 deg Tibialis posterior 55 g 2.4 cm 21 cm² 15 deg Tibialis anterior 70 g 7.3 cm 9.1 cm² 5 deg Rectus femoris 90 g 6.8 cm 12.5 cm² 5 deg Vastus lateralis 210 g 6.7 cm 30 cm² 5 deg Vastus medialis 200 g 7.2 cm 26 cm² 5 deg Vastus intermedius 180 g 6.8 cm 25 cm² 5 deg 42 14

15 Moments of muscles Depend on the force and on the moment arm length (i.e. the normal line from the joint center to the muscle force vector). Change with the joint angle Calculation of human movement Get the anthropometric data Get the mechanical properties of materials Define the acting forces Define the boundary conditions Solve the equations of movement 45 15

16 Example showing the complexity of anthropometric data

17 Example of presence of biomaterials in the tissues 49 Forces acting on the kinetic chains Gravity : fall, walking, diving Friction:resistance to body progression in air, water... Muscle force under nervous system control: push off in walking, antigravific,, antagonist, agonist Internal linking forces (tension developed by ligaments and/or transmitted by contact surfaces) Ground reaction, impact with obstacles 50 Forces acting on the kinetic chains The main difficulty is the force delivered by the muscle!!! Scheme of energy flow through the muscles O 2 CO 2 Metabolic energy uptake expired heat of contraction, activation, maintenance heat labile stable, shortening Mechanical energy Muscle tension loss due to cocontraction or absorption by muscles at another joint Increase in segment energies EXTERNAL WORK 51 17

18 Equations of movement Based on the classical laws of mechanics Different levels of complexity rigid body mechanics with joints (body decomposed into rigid elements with kinematic constraints) deformable solid mechanics with joints (the different elements of the body model can deform with kinematic constraints) Use of softwares to solve the equations 52 18