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Mechanics of Sprinting

Mechanics of Sprinting. D. Gordon E. Robertson, Ph.D. Biomechanics, Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, CANADA. Domains. Temporal Time and durations Kinematic Motion description, e.g., range of motion, speed, acceleration Kinetic

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Mechanics of Sprinting

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  1. Mechanics of Sprinting D. Gordon E. Robertson, Ph.D. Biomechanics, Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, CANADA

  2. Domains • Temporal • Time and durations • Kinematic • Motion description, e.g., range of motion, speed, acceleration • Kinetic • Causes of motion, e.g., forces, work, power

  3. Temporal Analysis • Race time • Stop watch • Timer • Videography (1 frame = 1/30th second) • Chronometer

  4. Donovan Bailey sets world record (9.835) despite slowest reaction time (0.174) of finalists

  5. Kinematic Analysis • Description of motion without consideration of its causes • Motion description • Based on Calculus developed by Newton and Leibnitz Isaac Newton, 1642-1727

  6. Kinematic Analysis manual goniometer • Linear position • Ruler, tape measure, optical • Angular position • Protractor, inclinometer, goniometer digital goniometer optical goniometer protractor

  7. Kinematic Analysis • Linear velocity • Radar gun • Speedometer • Videography • Angular velocity • RPM • Videography radar gun

  8. Kinematic Analysis • Linear acceleration • Accelerometer • Videography • Angular acceleration • Videography accelerometers

  9. Motion Analysis • Cinefilm, video or infrared video • Athlete is filmed and locations of joint centres are digitized • body is modeled as a system of connected segments high-speed cine-camera

  10. Motion Analysis Biomechanics Laboratory

  11. Computerized Digitizing Ariel Performance Analysis System

  12. Stick Figure Animation

  13. Start Phase • No motion permitted when gun sounds • No force on blocks 0.10 seconds before gun sounds • Gun fires and there is a delay before sprinter hears gun (unless blocks have speakers) • Delay between when gun fires and force is applied to blocks (time for message to reach muscles at 6 m/s) • Taller sprinters take longer to start

  14. Acceleration Phase • Each athlete has his/her own rate of acceleration • The whole race takes between 43 and 48 steps • At maximum speed, stride length (1 stride = 2 steps) is over 4.5 metres long! • Can last to 70 metres

  15. Last 60 Metres of Race

  16. Constant Velocity Phase • athletes achieve maximum, constant velocity between 50 and 70 metres • speed: • 9 – 12 metres / second • 32 – 43 kilometres / hour • foot achieves twice this velocity (86 km/h!)

  17. Fastest Sprinter (in 1996)Johnson or Bailey? • Johnson’s 200 m record = 19.32 s • Each half = 9.66 s? • Bailey’s 100 m record = 9.84 s • US reporters claim Johnson is faster? • Johnson had running start for last 100 m • At 12 m/s Bailey can run 100 m in 8.33 s, 200 m time could be 18.17 (new WR)! • race in Toronto confirms Bailey is Fastest Man in the World

  18. Kinetic Analysis Causes of motion • forces and moments of force • work, energy and power • impulse and momentum • Inverse Dynamics derives forces and moments from kinematics and body segment parameters (mass and centre of gravity)

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

  20. 20. Flexing 0. -20. Trial: SR11BJ Extending Ang. vel. Net moment Flexor 300. Power 0. -300. Extensor Power (W) Moment (N.m) Angular vel. (/s) Concentric 2000. 0. -2000. Eccentric ITO CFS CTO IFS -4000. 0.0 0.1 0.2 0.3 0.4 Time (s) • Hip angular velocity & power • initial burst of power to create swing • 3000-4000 W peak power by iliopsoas and rectus femoris • latter burst to drive leg down • 2800-3600 W peak power by gluteals

  21. 20. Extending 0. -20. Trial: SR11BJ Flexing Ang. vel. Net moment Extensor 300. Power 0. -300. Flexor Power (W) Moment (N.m) Angular vel. (/s) Concentric 2000. 0. -2000. Eccentric ITO CFS CTO IFS -4000. 0.0 0.1 0.2 0.3 0.4 Time (s) • Knee angular velocity & power • initial burst of power to stop flexion by muscle block not by knee muscles • small burst for extension • final burst to stop extension by eccentric contraction of hamstrings

  22. Questions?

  23. Thank you

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