Biomechanics of Walking and Sprinting

1
Biomechanics of Walking and Sprinting

• D. Gordon E. Robertson, PhD, FCSB
• Biomechanics, Laboratory,
• School of Human Kinetics,
• University of Ottawa, Ottawa, CANADA

2
Quantitative Domains

• Temporal
• phases (stance/swing) and events (foot-strike,
  toe-off), stride rate
• Electromyography
• muscle activation patterns
• Kinematic (motion description)
• stride length, velocity, ranges of motion,
  acceleration
• Kinetic (causes of motion)
• ground reaction forces, pressure patterns, joint
  forces, moments of force, work, energy and power

3
Temporal Analysis

• Stride time (s)
• Stride rate 1/time (/s)
• Stride cadence 120 x rate (b/min)
• Instrumentation
• Photocells and timers
• Videography (1 frame
  1/30 second)
• Metronome

4
Electromyography
Noraxon system
Bortec system
Delsys electrodes
Mega system
5
Donovan Bailey sets world record (9.835) despite
slowest reaction time (0.174) of finalists
6
Gait Characteristics - Walking
7
Gait Characteristics Running/Sprinting
8
Kinematic Analysis

• Linear position
• Ruler, tape measure, optical, potentiometric
• Linear velocity
• radar gun, photo-optical timer
• Linear acceleration
• Accelerometry, videography

3D digitizer
radar gun
miniature accelerometers
9
Kinematic Analysis
manual goniometer

• Angular position
• Protractor, inclinometer, goniometer
• Angular acceleration
• Videography

digital goniometer
optical goniometer
10
Motion Analysis

• Cinefilm, video or infrared video
• Subject is filmed and locations of joint centres
  are digitized

Panasonic videocamera
Vicon infra-red camera
11
Computerized Digitizing (APAS)
12
Stick-Figures of aKarate Front Kick
13
Computerized Digitizing(SIMI)
14
Real-time Digitizing (Vicon or MAC EvaRT)
15
Full-body 3D Marker Set
16
Gait and Movement Analysis Lab (uOttawa)

• Vicon MX Workstation
• 7 Vicon MX-13 cameras
• 3-6 force platforms
• 1-3 Bortec 8-channel EMGs
• F-Scan in-shoe pressure system

17
3D Geometric Model(Visual3D)
18
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,
  centre of gravity, and moment of inertia)

19
Force Transducers
20
Force Platforms
Kistler force platforms
21
Steps for Inverse Dynamics

• Space diagram of the lower extremity

22
Divide Body into Segments and Make Free-Body
Diagrams

• Make free-body diagrams of each segment

23
Add all Known Forces to FBD

• Weight (W)
• Ground reaction force (Fg)

24
Apply Newtons Laws of Motion to Terminal Segment

• Start analysis with terminal segment(s), e.g.,
  foot or hand

25
Apply Reactions of Terminal Segment to Distal End
of Next Segment in Kinematic Chain

• Continue to next link in the kinematic chain,
  e.g., leg or forearm

26
Repeat with Next segment in Chain or Begin with
Another Limb

• Repeat until all segments have been considered,
  e.g., thigh or arm

27
Normal Walking Example

• Female subject
• Laboratory walkway
• Speed was 1.77 m/s (fast)
• IFS ipsilateral foot-strike
• ITO ipsilateral toe-off
• CFS contralateral foot-strike
• CTO contralateral toe-off

28
Ankle angular velocity, moment of force and power
Dorsiflexion
Trial 2SFN3
Plantar flexion
Ang. velocity
Moment

• Dorsiflexors produce dorsiflexion during swing

Power
Dorsiflexors
Plantar flexors

• Plantar flexors control dorsiflexion

Concentric

• Large burst of power by plantar flexors for
  push-off

Eccentric
IFS
CTO
CFS
ITO
CFS
ITO
29
Knee angular velocity, moment of force and power
Extension
Trial 2SFN3
Flexion
Ang. velocity

• Negative work by flexors to control extension
  prior to foot-strike

Moment
Power
Extensors
Flexors

• Burst of power to cushion landing

Concentric

• Negative work by extensors to control flexion at
  push-off

Eccentric
IFS
CTO
CFS
ITO
CFS
ITO
30
Hip angular velocity, moment of force and power
10
Flexion
0
Trial 2SFN3
Extension
-10
Ang. velocity
Moment

• Positive work by flexors to swing leg

Power
100
Flexors
0
Power (W) Moment (N.m)
A ng. Vel. (rad/s)
Extensors

• Positive work by extensors to extend thigh

-100
Concentric
100
0

• Negative work by flexors to control extension

Eccentric
-100
IFS
CTO
CFS
ITO
CFS
ITO
-200
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Time (s)
31
(No Transcript)
32
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
33
Stick Figure of Sprinter
34
Start Phase

• No motion permitted when gun sounds
• No force on blocks for 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

35
Acceleration Phase

• Each athlete has his/her own rate of acceleration
• The whole race takes between 42 to 48 steps (21
  to 24 strides)
• At maximum speed, stride length (1 stride 2
  steps) is over 4.5 metres long!
• Can last to 70 metres

36
Last 60 Metres of Race
37
Constant Velocity Phase

• athletes achieve maximum, constant velocity
  between 50 and 70 metres
• speed
• 9 to 12 metres / second
• 32 to 43 kilometres / hour
• foot achieves twice this velocity (86 km/h!)

38
Fastest Sprinter (in 1996)Johnson or Bailey?

• Johnsons 200 m record 19.32 s
• Each half 9.66 s?
• Baileys 100 m record 9.84 s
• US reporters claimed Johnson was faster?
• Johnson had running start for last 100 m
• At 12 m/s Bailey runs 100 m in 8.33 s, 200 m
  time could be 18.17 (new WR)!
• race in Toronto confirmed Bailey was Fastest Man
  in the World

39
Stride Analysis

• swing phase of one leg
• world-class male sprinter
• 50 m into 100 m competitive race (t 10.06 s)
• analysis of hip and knee only (ankle forces not
  significant during swing)

40

• 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

41

• 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

42
Questions?