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 = 1/30th 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, 1642-1727

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-speedcine-camera

Motion AnalysisBiomechanics 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

40

50

60

70

80

90

100

5 6 7 8 9 10 11Race time (s)

female: 10 m/s

male: 12 m/s

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 = 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

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)

0.0 0.1 0.2 0.3 0.4Time (s)

-4000.

-2000.

0.

2000.

-300.

0.

300.

-20.

0.

20.

Pow

er

(W)

Mom

en

t (N

.m)

A

ng

ula

r vel.

(/s

)

Trial: SR11BJAng. vel.Net momentPower

ITO CFS CTO IFS

Flexing

Extending

Flexor

Extensor

Concentric

Eccentric

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

0.0 0.1 0.2 0.3 0.4Time (s)

-4000.

-2000.

0.

2000.

-300.

0.

300.

-20.

0.

20.

Pow

er

(W)

Mom

en

t (N

.m)

A

ng

ula

r vel.

(/s

)

Trial: SR11BJAng. vel.Net momentPower

ITO CFS CTO IFS

Extending

Flexing

Extensor

Flexor

Concentric

Eccentric

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

Questions?

Thank you