Lecture 14, Biomechanical Analysis Flashcards
Biomechanical Analysis (what is it?)
- analysis involves breaking something into smaller parts and then examining those parts
- teachers and coaches observe their athletes and students performing and describe the mechanical characteristics of the performance - provide feedback
- comparative descriptors after often used to describe these characteristics
my notes:
- look at different elements of movements to understand what you look like and how that contributes to performance to affect success or not (difference between hitting the target or missing the target)
- often we will have a comparison of what you should look like and why to improve performance (adjust your form, to being more accurate, idealized form or can better hit the target now)
Biomechanical Analysis (what type of analysis is it?)
if human movement or any of its aspects is described without measuring or quantifying those characteristics, the resulting analysis in qualitative
- analysis cannot be subjective - need to provide specific details each and every time
- bringing more objectivity and reliability
- task sheet to find out how different parts of the body work together (head action, trunk action, arm action and leg, action) and define different parts of movement (how do you go from preparation to action and then how do you follow through) - write very specific details
- can see how body parts align at different parts of the movement
- you are not just saying something is bad but the fact that someone is not successful and with the help of the task sheet you can tell them at what exact point they were not successful
- key is to have a document where you can note the movements for qualitative analysis
Qualitative Analysis of Movement
important to understand what is happening and when
- movement is divided into phases on a task sheet
◦ preparatory, movement, and follow-through
- the body is divided into different segments on a task sheet
◦ examine how the athlete puts everything together
- you can use the task sheet to identify where the problem is
◦ which individual component was the key to success
my notes:
- have a document for qualitative, object analysis (can divide it according to movements and different body parts)
- the task sheet provides you with something concrete that you can reflect upon (circle the problem exactly)
- good when movements are simple, slow, repetitive and easy
Biomechanical Analysis (what does it become when it described with #’s)
- if human movement or any of its aspects is described with numbers, the resulting analysis is quantitative
- the variables measured may be temporal (looking at timing), kinematic (position, displacement, velocity, acceleration), or kinetic (force, energy, work, power)
- some sort of instrument is used to measure the variable
- the instrument itself and the setting that it is used in may affect the performance of the athlete, patient, or client
- the process of measuring something influences the parameter being measured
my notes:
- when movement starts to speed up and get more complicated - you lose detail and ability to describe what is happening but we can use tools to help us (need to use tools to help you analyze - camera for example)
- can lose detail as movement gets faster as it can become a blur
- can look at force platforms, strain gauge, timing tools that measure acceleration, displacement, velocity, smart watches, cameras
Data Collection in a Lab or Field Setting (what are the pros and cons of each approach?)
lab: with tools we can measure performance in lab setting - advantages is that is a highly controlled environment to measure the performance without external influence, access to equipment which gives lots of information - some disadvantages are that it is not where the actually activity is preformed so it cannot be accurate (variations in real activity that can have a affect like the up and downhill portions of a marathon cannot be recreated in the lab), knowing that you are being observed has an affect on performance (can change how you normally go about doing the activity), more comfortable doing your own thing
field: performing in field like setting has downsides like weather, tools you use out in the field tend to be simpler so you do not get as precise information but sometimes you do not have access to lab so field becomes the most practical option and cost can play a role into it as well
Data Collection (what can you use?)
tools for measuring biomechanical variables can vary in sophistication and cost from simple watches to complicated platforms
- popular tools for measuring kinematic variables include:
◦ timing systems
◦ velocity-measuring systems
◦ accelerometers
◦ motion analysis trackers
- kinetic variables are based on force, which can be measured using:
◦ force platforms
◦ strain gauges
◦ pressure-sensing devices
- camera is the best thing you can use in biomechanics as timing, velocity and acceleration can be found if you took a couple of pictures and put all that together (camera, ruler and calculator is all you need to do very detailed analysis)
- the details are so key because it can be the difference between success and failure - sometime if people do too much that becomes problematic (was there more rotation at shoulder versus elbow, is there too much rotation at the wrist) and sometimes you look more the absence of stuff
Assessing Performance
- technique determines performance
◦ improvement comes from attention to detail - biomechanics is about understanding those details
◦ details about key movements
◦ details about important non-movements
◦ details about movement relationships - motion capture is a technique that allows for study of those details
- motion capture is the process of using video or picture cameras to gather images and study a moving system (and its constituent parts)
- taking pictures is the single biggest tools you can use - multiple pictures is key as it is the ability to freeze movement in time that is very important to analysis (usually use video camera)
Motion Capture Setup (Hz)
video provides limited quantitative data
need the ability to look at individual frames
the type of camera used for analysis is key to the process
the camera must generate pictures with a lot detail (resolution)
the camera must be able to to take multiple pictures every second (capture rate)
- human eyes (24 Hz) - 24 pictures get sent to your brain
- commercial cameras (30 Hz) - can take pictures at a rate of 30 times per second (typical camera) - good for slow
- high speed cameras (500 to 10,000 Hz) - golf movement and football to get that quality of movement because if you can see it you can understand it (if you cannot see it everything is just a blur)
- using a video camera that allows you freeze and stops movement in time is Hz (how many times did something happen per second)
- for fast movements you need to takes pictures at high speed cameras
Motion Capture Setup (computer vs camera)
what the camera “sees” - reflect markers are fixed to the body and indicate segment or joint position
what the computer “sees” - analysis is done is a stick figure, which shows “subtle” changes in position
- you do not care about the person you care about different parts on the body
- the markers move with the whole body
- the markers reflects body part or segment
- stick figure represents all the body parts as they move from one part of the task to the next on the computer
Motion Capture Setup (perspective and how it should be setup?)
perspective is everything
which event is in a better position to be analyzed?
the camera should always be:
- 90° to plane of motion
- placed on a tripod - camera should not move as only the performer should move (when camera moves then you begin to measure that, the cameras change and no longer the performer) - makes us sure of what we are measuring
- far enough away to capture the entire movement but close enough to see the body
- you lose the depth of the performer if you are not taking it in 90 degrees to the plane of action
- tend to stand further back for beginners as you are looking at bigger mistakes and not tiny details they are not concerned with whereas for advanced you stand closer to because you want to know the small details and to be specific (elite athlete you want to be right up close to differentiate between tiny details as there is a certain position they need to adopt and the body parts all need to be positioned in a certain way)
Camera Position and the Planes of Motion (3)
where should the camera be positioned when moving in the…
- the camera is always in line with the axis of rotation - always faces axis of rotation
- camera is in left or right for mediolateral axis - if you are in sagittal plane you are running and flexing, the camera will always face the axis of rotation meaning you can analyze the right or left side of the body
- if it is anterioposterior axis the camera is in front of back (jumping jack - abduction and adduction)
- camera above or below for longitudinal axis (position of your shoulders as you rotate for camera above)
- put camera further away to analyze big parts of the body and closer to analyze parts of the body based on the amount of details you want
Motion Capture Setup (other things to consider)
- one camera will record two-dimensional or planar motion (forward/back, up/down for example)
◦ two or more cameras are used to record three-dimensional actions (kicking soccer ball, when you are moving foward/back and twisting you will need two cameras or more) - performers often wear spandex suits or tight fitted clothing
◦ reflective markers attached to the suit will move as the limb or body segments move (so that the markers do not sway with clothing movement) - do not care about the person it is the parts of them and you want to make sure the clothing is not moving rather the body parts which means this helps with reliability and clarity with data - high speed analysis requires good lighting for clear pictures
◦ if you can’t see the markers, you lose data points
◦ light sources or sun blockers are helpful - being in lab setting is helpful to control for that
◦ if you cannot see it is not happening and that is why the reflective markers are bright (pop or shine)
Analyzing Movement (what 3 tools are most needed?)
although motion analysis is an expensive and time-consuming process, it is possible to take some basic measurements using a few simple tools
- using a camera, a calculator, and a ruler, we can generate some kinematic data on an athlete running through the picture frame (can do complicated biomechanical analysis with this equipment)
Analyzing Movement (time stamp)
first, we need to know when things happened in time
- the video camera sampled the data at 15 Hz
◦ 15 pictures were taken every second
◦ each picture represents 1/15th of a second
- the time stamp is the time interval between pictures
◦ the time between each picture is 0.0667 s
- to calculate movement time:
◦ multiply the frame number by the time stamp (0.0667)
◦ OR divide your frame number by 15 (sampling rate)
- it is not just knowing where you are but also when you are (qualify stuff and performance)
- time stamp is when things happen in time - the difference between one frame and the other (if you know what picture you are looking at, you know exactly when it happened in time) - multiply picture number by our time stamp which gives us timing of movement
- the camera is reliable but you need to know often takes pictures
Analyzing Movement (fixed vs moving reference)
- next, we need to determine the positions of the body in space
◦ this requires a spatial reference system - fixed reference: describes the movements relative to the environment or space - how high up y or far along x (good when you want to measure performer with respect to environment and measure one performer with respect to another performer because you use an absolute performance where you measure everyone the exact same way) -this is what most performances uses as it easy and can compare between people
- moving reference: examines the movement of a body segment (cartesian coordinate system is put onto body parts where as person moves the x and y axis will move and shift as they are aligned with position of tibia for example)
- need to know how you are moving in space - cartesian coordinate system
- nothing is better but its better to be consistent - most studies used fixed
