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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
Mechanics of Sprinting

D. Gordon E. Robertson, Ph.D.

Biomechanics, Laboratory,

School of Human Kinetics,

University of Ottawa, Ottawa, CANADA

domains
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
Temporal Analysis
  • Race time
    • Stop watch
    • Timer
    • Videography (1 frame = 1/30th second)
    • Chronometer
kinematic analysis
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 analysis7
Kinematic Analysis

manual goniometer

  • Linear position
    • Ruler, tape measure, optical
  • Angular position
    • Protractor, inclinometer, goniometer

digital goniometer

optical goniometer

protractor

kinematic analysis8
Kinematic Analysis
  • Linear velocity
    • Radar gun
    • Speedometer
    • Videography
  • Angular velocity
    • RPM
    • Videography

radar gun

kinematic analysis9
Kinematic Analysis
  • Linear acceleration
    • Accelerometer
    • Videography
  • Angular acceleration
    • Videography

accelerometers

motion analysis
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 analysis11
Motion Analysis

Biomechanics Laboratory

computerized digitizing
Computerized Digitizing

Ariel Performance Analysis System

start phase
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
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
constant velocity phase
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
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
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
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)
slide21

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
slide22

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