mechanics of sprinting d. gordon e. robertson, ph.d. biomechanics, laboratory, school of human...
TRANSCRIPT
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