Transcript Kinetics versus kinematics for analyzing coordination

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
manual goniometer
• Linear position
– Ruler, tape measure, optical
• Angular position
– Protractor, inclinometer,
goniometer
optical goniometer
protractor
digital 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
100
male: 12 m/s
90
80
70
female: 10 m/s
60
50
40
5
6
7
8
9
Race time (s)
10
11
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?
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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)
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
20.
Flexing
0.
-20.
300.
Trial: SR11BJ
Ang. vel.
Net moment
Power
Extending
Flexor
0.
-300.
2000.
Extensor
Concentric
0.
-2000.
Eccentric
-4000. ITO
0.0
CFSCTO
0.1
0.2
Time (s)
IFS
0.3
0.4
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
20.
Extending
0.
-20.
300.
Trial: SR11BJ
Ang. vel.
Net moment
Power
Flexing
Extensor
0.
-300.
2000.
Flexor
Concentric
0.
-2000.
Eccentric
-4000. ITO
0.0
CFSCTO
0.1
0.2
Time (s)
IFS
0.3
0.4
Questions?
Thank you