Introduction to Biomechanics EXSC 408L - Fall ‘10 Dr. Kathleen E. Sand (BU 2007; USC 2004) subject line: EXSC 408L … Office Hours (PED B7) TUES PM WED 1145AM - 145PM & by appointment Course Reader: Selections from “Biomechanics of Sport” by D. Miller & R. Nelson Lab website

Proposed Semester Schedule Fall 2010

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.)

LoadingTippingPushingFlight Entry preparation Biomechanics Research 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 Assess athlete’s physical 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 technique that complements athlete’s capacity How are they going to get there? Coach / Athlete / Clinician-Driven Performance or injury-related issue? Identify critical factors that improve task performance Mechanical objective Provide mechanical basis for implementing individualized training / technique modifications

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 Frontal Plane stationary Time 1 Time 2 Hipextension Kneeextension Trunk Lateral Flexion Pelvis SupinationPronation Hip Adduction

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 = (p 2 -p 1 )/(t 2 -t 1 ) –Horizontal Velocity; V h = (x 2 -x 1 )/(t 2 -t 1 ) –Vertical Velocity; V v = (y 2 -y 1 )/(t 2 -t 1 ) –Resultant Velocity; V r = √V h 2 + V v 2 Acceleration (vector) Rate of change in velocity; a = (v 2 -v 1 )/(t 2 -t 1 ) Horizontal, Vertical, Resultant VhVhVhVh VrVrVrVr VvVvVvVv

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)  Shank  Elbow

Angular Kinematics Angular Velocity (  ) rate of change in angular position  = (  2 -  1 )/(t 2 -t 1 ) Angular Acceleration (  ) rate of change in angular velocity  = (  2 -  1 )/(t 2 -t 1 )  Time 1 Time 2

Newton’s Laws 1 st Law: Inertia An object in motion (rest) tends to stay in motion (rest) unless acted upon by an external force. 2 nd 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. 3 rd 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