Introduction to Biomechanics
EXSC 408L - Fall ‘10
• Dr. Kathleen E. Sand (BU 2007; USC 2004)
• Kcosta@usc.edu
• Email subject line: EXSC 408L …
Office Hours (PED B7)
• TUES 230 - 430PM
• WED 1145AM - 145PM
• & by appointment
• Course Reader:
Selections from “Biomechanics of Sport” by D. Miller & R. Nelson
• Lab website
•
http://www.usc.edu/dept/LAS/kinesiology/exsc408l/lab/lab.html
Proposed Semester Schedule
Fall 2010
Date
Lectures
Monday
Wednesday
Applications & Significance cause-effect (total body
/ M otion Analysis
level)
Lab Exercises
Reading
Introduction & Lab 1:
8/23, 25
Computer Skills
Ch's 2 & 3
Intro to M otion Analysis /
linear motion / linear
gait analysis & terminology /Linear Kinematics / Total Body
8/30, 9/1
kinematics
PROJECT: Pre-Proposals
Center of M ass
p. 39-48
9/6, 8
LABOR DAY
PROJECT: Brainstorming
Angular Kinematics
p. 39-48
9/13, 15
linear impulse
PROJECT: pre-proposals
Linear Impulse & M om entump. 49-61
Angular Impulse &
9/20, 22
angular impulse
projectile m otion
M omentum
p. 49-61
EXAM #1 (proj. proposals
biomechanics methods: real9/27, 29
due)
w orld apps
Total Body Kinetics: F=ma
P. 53-61
PROJECT: data colleciton motion analysis (w hole body
10/4, 6
prep
/ actual data)
PROJECT: Data collection
PRACTICAL EXAM & Project
10/11, 13
motion analysis (joint level)cause-effect (segment level)data return
10/18, 20
New ton's Law s of M otion New ton's Law s of M otion Joint Kinetics
p. 61-72
10/25, 27
Joint Kinetics
ex ercise applications
Project Analysis #1
11/1, 3
Joint Kinetics
clinical applications
Project Analysis #2
11/8, 10
REVIEW
EXAM #2
Project Analysis #3
11/15, 17
scientific presentation skills scientific presentation skills Project Analysis #4
11/22, 24
Sport Science Apps.
PROJECT: Analysis
Project Analysis (indep)
11/29, 12/1
Injury Biomechanics Apps REVIEW
Project Presentations
FINAL EXAM: Friday, Dec. 10th, 2-4PM
Biomechanics
Uses Newton’s Laws to analyze the cause-effect
relationships of human movement
Clinical – gait, rehab, prosthetics
Ergonomic – lifting, repetitive motion tasks, work areas,
auto design
Sport – performance enhancement, injury diagnosis &
prevention, performance prosthetics, implement
design (shoes, pads, helmets, clubs, landing mats,
bikes, etc.)
Biomechanics Research
Loading
Tipping
Pushing
Flight
Entry
preparation
Using Newtonian mechanics to understand and characterize
human motion in order to improve task performance and decrease
injury potential.
- complex, mulit-joint movements
- specific mechanical objectives
- well-practiced tasks & highly skilled performers
- identify control strategies / parameters
- apply to broader populations within varying contexts
Problem-Solving Approach
Coach / Athlete / Clinician-Driven
Performance or injury-related
issue?
Assess athlete’s physical
Provide mechanical basis for
implementing individualized
training / technique
modifications
Identify technique that
complements athlete’s
capacity
How are they going to get
there?
capacity
(eg. control & coordination)
Current state of the system
Identify mechanics
athlete uses to generate and
control total body momentum
within specific context
Individual solution space
Identify critical factors
that improve task
performance
Mechanical objective
Components of Biomechanics
Kinematics
Study of spatial and temporal aspects of human
movement
Linear & Angular position, velocity, acceleration
Kinetics
Study of forces and torques involved in human
movement
Linear & Angular forces, torques, impulse, power, work
Components of Biomechanics
Kinematics
Branch of mechanics
involving Motion
Analysis,
quantifying movement
characteristics without
considering forces
that cause the motion
Temporal & Spatial
characteristics
(i.e. position, velocity,
acceleration)
Qualitative or
Quantitative
Linear & Angular
Kinetics
Branch of mechanics
that investigates the
forces that cause
motion
(e.g. ground reaction
forces, net joint
forces, impulse)
More Quantitative than
qualitative
Linear & Angular
Quantitative vs. Qualitative Analysis
Quantitative
– Calculating absolute values for variables
of interest
– …approach velocity of 10m/s
Qualitative
– Non-numerical descriptive analysis for
variables of interest
– …increased forward trunk lean during
approach
Biomechanical Tools
Quantitative Analysis
- Video & review
- Motion Analysis
Software
- Force Plates
- Power Rack
- Electromyography
(EMG)
- Computer Modeling
Qualitative Analysis
- Video & review
- Motion Analysis
Software
Videography
Quantitative Filming
• (2D) Stationary Camera
• (3D)  2 cameras
• View perpendicular to
plane of motion
• Calibration object of
known length
• Know the playback
rate of your camera,
VCR and/or computer
video card (standard
30 fps)
• Step rate, step length,
joint & segment angles,
velocities
Qualitative Filming
• Desired field of view for
motion of interest
• Understand analysis
limitations (parallax)
and strengths (setup
time, overall picture)
• Body & segment
orientation in space or
relative to equipment,
general technique
description
Planes & Axes of Motion
Planes of Motion
Sagittal Plane
stationary
Frontal Plane
stationary
Observable Joint Motion
Sagittal Plane
stationary
Time 1
Frontal Plane
stationary
Time 2
Hip
extension
Hip
Adduction
Trunk
Lateral Flexion
Pelvis
Knee
extension
Pronation
Supination
Sport Biomechanics
Investigate the influence of technique on …
–Force generation (ground reaction &
muscle)
–Mechanical loading (across joints)
–Injury (potential factors and prevention)
–Event performance
How does Biomechanics facilitate
performance?
• Provides coaches & athletes with the tools to answer
questions regarding event technique & performance
(i.e. critical zones & critical performance variables or
factors)
• Uses mechanically-based principles to develop a
relationship between
– task objectives (mechanical), and
– athlete characteristics (e.g. muscular strength, joint
range of motion, coordination).
In order to identify athlete specific solutions or
strategies to achieve event goals.
Applications & Significance
• Critical problem-solving skills
• Sport - e.g. coaching, sport-science, personal
training
• Clinical - e.g gait analysis lab, PT, OT, prosthetics
• Ergonomic - e.g equipment design (auto),
insurance consulting, workplace environment
• Corporate / Technology - e.g. forensics, footwear,
golf, helmet design, etc.
• Education
• Technology - 3D motion capture for animation
(movies & gaming)
• Simulation (modeling) vs. Animation
Linear Kinematics - Variables
Position
where an object is in space relative to a global coordinate
system
Displacement
change in an object’s position independent of direction
Velocity (vector)
rate of change in position; V = (p2-p1)/(t2-t1)
–
Horizontal Velocity; Vh = (x2-x1)/(t2-t1)
Vh
–
Vertical Velocity; Vv = (y2-y1)/(t2-t1)
–
Resultant Velocity; Vr = √Vh2 + Vv2
Vr
Vv
Acceleration (vector)
Rate of change in velocity; a = (v2-v1)/(t2-t1)
Horizontal, Vertical, Resultant
Angular Kinematics
Angular Position ()
Segment Angle
angle of a segment relative to a
fixed reference (e.g. shank angle
relative to right horizontal
anchored at the ankle joint)
Joint Angle
relative angle between two
adjacent segments
(e.g. upper arm & forearm
compose elbow angle)
 Elbow
 Shank
Angular Kinematics
Angular Velocity ()
rate of change in angular
position
 = (2-1)/(t2-t1)
Angular Acceleration ()
rate of change in angular
velocity
 = (2-1)/(t2-t1)
Time 2
Time 1

Newton’s Laws
1st Law: Inertia
An object in motion (rest) tends to stay in motion (rest)
unless acted upon by an external force.
2nd Law: F = ma
The acceleration of an object of constant mass is
proportional to the sum of forces acting upon the object’s
center of mass.
3rd Law: Conservation of Momentum
When a force is applied to an object there is an equal
and opposite reaction force.
…Practical Applications?
Divisions of Mechanics
Statics
Study of systems with zero acceleration (a = 0), at rest or
in a constant state of motion.
F = ma = 0
Dynamics
Study of systems in motion, with non-zero acceleration
F = ma