Transcript Gait Analysis (1)

Analysis methods and tools
• Reading assignment:
• Kreighbaum, Ch 9, 17
• Outline
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Observing and analyzing human performance
Putting details into a broader context – the model
General analysis methods: qualitative and quantitative
Specific analysis methods and tools
• Kinematic: timers, videography and other imaging, electrogoniometry
• Kinetic: dynamometers, force transducers, force platforms, pressure
sensors, accelerometers
• Electromyography
– Examples of analysis tools in research
• Timer and video analysis – Harms poster during break
• Strain gauge and video – slides on bat bending study
• Accelerometry – tennis vibration study
Observing and Analyzing Performance
• The Nature of Skills
– Movement patterns - a general series of movements having
common elements. Ex: running, jumping, walking, throwing,
striking, pushing
– Skill - adaptation of general movement pattern to constraints of a
particular task. Ex: high jump, baseball hitting, softball pitching
– Technique - a particular type of the same skill. Ex: power hitter,
contact hitter
– Style - individual adaptations of a technique. Ex: short
backswing, no stride
– Constraints - limitations associated with the event. Ex: rules,
equipment, environment, limitations of performer.
Observing Performance (cnt’d)
• Classification of Skills According to type of
environment:
– Open - unpredictable environment. Ex. baseball
hitting, jump shot
– Closed - predictable environment. Ex: free throw, golf
shot, high jump
• Classification according to how it is done
– Discrete - definite beginning and ending. Ex: jump
shot, shot put, high jump
• Repeated discrete - assembly line, tennis forehand. (Subject to
repetitive motion disorders)
– Continuous - no definite beginning and ending. Ex:
running, walking, work tasks
Oberving performance (cont’d)
• Observing Skill Performances
– Discrete skills - divide into phases such as (1) preparation, (2) execution, (3)
follow-through/recovery
– Continuous/cyclic - select one cycle and divide it into phases. Ex: support,
swing phases in walking
• The global analysis (holistic model)
– Identify overall performance objective (OPO) –(Table next slide)
• When two or more objectives are identified, priority must be set (e.g., speed vs
accuracy
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Divide skill into discrete parts. Ex. Stance, stride, swing, follow-through
Identify the mechanical purpose (MP) of each discrete part
List the biomechanical factors and principles. Ex:: momentum conservation
List the critical features of each part - movements that must be performed for
successful execution of the skill (keys to focus on, e.g., knee extended at
impact)
• Example – article on baseball hitting
Analysis Models – the context
and the why?
• Holistic – same as Kreighbaum, Adrian p. 18-19
– Read literature and use prior experience to figure out
what to focus on (ex: handout on baseball hitting)
• Factors-results – Adrian p. 17-18
– Analytical, heirarchial, deterministic
– Only useful for goal-oriented skills
– Example – article by Hay on swimming starting
techniques
Analysis Methods
• Qualitative vs quantitative
– Types and precision of data needed, not the tool
available, dictates selection of tool
• Naked-eye observational procedures
– Observational plan necessary to be consistent and
reliable
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View multiple times
View from multiple perspectives
Focus on parts, then whole, then parts
Form a visual-mental image of the performance
Use a checklist – borrow or construct your own
Constructing Analysis Checklists
• Procedures
– Study other checklists. Refer to specific sports/skills chapters in
textbooks
– Read literature to determine what factors are important
– List the determinants of skilled and unskilled actions
– Arrange checklist in a scale (dichotomous, continuum)
• Common factors usually included in checklists
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Location of COM relative to base of support
Width of base of support
Range and path of movement of various body segments
Sequencing of segment movements
Projection angle of objects released or struck & total body COM
Overall perception of movement’s effectiveness, smoothness, etc.
Videographic and Cinematographic Analyses
• Qualitative procedures
– Contourograms
– Point plots
– Stick figures
• Quantitative analysis -the process (Hu-M-An)
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Videotaping
Frame grabbing – converting images to digital form
Digitizing – locating segment endpoints in space and time
Calculations done by computer
• Applying the multiplier or converting coordinates to life size
• Smoothing coordinates
• Calculating parameters for each segment and body COM
– Linear displacement, velocity, acceleration and inverse dynamics
– Angular displacement, velocity, acceleration and inverse dynamics
• Displaying output (Digital as well as graphic)
Other Analysis Procedures
• Optoelectric imaging
– Active or passive markers (Vicon brochure)
• Dynamographic analysis (slides on force platform)
– Force platforms, load beams, strain gauges
• Accelerometric analysis (slides on racquet vibrations)
– Vibrations, impacts, rapidly changing motions
• Electrogoniometric analysis
– Joint and segment angles
• Electromyography
– When and to what degree is a muscle active?
– Fatigue estimate
Begin swing: 183 ms PC
Bat Vibrations During Swing & Impact
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Peak 41 ms PC
Begin Swing
233ms PC
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Horiz Pk 38 ms PC
Strain (v)
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Time (s)
Horiz Dir
Vert Dir
Magnitude
Horiz Dir
Vert Dir
Magnitude
0.7
Bending Direction During Swing & Impact
250
Beg Sw - 233 ms PC
200
Direction (deg)
150
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O is horiz & back - 21 ms PC
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Time (s)
0.5
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Approximate position when peak bending and
Peak torque occurs ~ 40 ms PC
Output of accelerometer mounted
on tennis racquet handle
Results of impact on end of racquet head on racquet handle accelerations
Time domain
Frequency domain