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 –Causes of motion, e.g., forces, work, power

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

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

Kinematic Analysis Description of motion without consideration of its causes Motion description Based on Calculus developed by Newton and Leibnitz Isaac Newton,

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

Kinematic Analysis Linear velocity –Radar gun –Speedometer –Videography Angular velocity –RPM –Videography radar gun

Kinematic Analysis Linear acceleration –Accelerometer –Videography Angular acceleration –Videography accelerometers

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

Motion Analysis Biomechanics Laboratory

Computerized Digitizing Ariel Performance Analysis System

Stick Figure Animation

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

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

Last 60 Metres of Race

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!)

Fastest Sprinter (in 1996) Johnson or Bailey? Johnson’s 200 m record = 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 (new WR)! race in Toronto confirms Bailey is Fastest Man in the World

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)

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)

Hip angular velocity & power initial burst of power to create swing W peak power by iliopsoas and rectus femoris latter burst to drive leg down W peak power by gluteals

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

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