HPE 340 In class tutorial 4 Qualitative analysis PDF

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HPE 340: Exercise Biomechanics

IN CLASS TUTORIAL 4 Qualitative analysis Objectives 1. Identify key events and phases in a movement 2. State key performance objectives and critical elements of a movement 3. Create an observational model 4. Gain experience in setting a video camera for optimal capture in biomechanics 5. Understand the key settings that affect biomechanical video capture quality 6. Qualitatively critique movement performance Background Qualitative analysis applies basic biomechanical principles in the assessment of human movement in the interests of improving performance and reducing risk of injury. As qualitative analysis is inherently subjective, the process of preparation, observation, evaluation and intervention is vital for a reliable analysis to be conducted.

Practical work Write a description of the performance objectives of a countermovement jump (CMJ) using a Vertec.

Achieve maximum height

References:Payton, C. J. & Bartlett, R. M. (2008). Biomechanical evaluation of movement in sport and exercise. Routledge, UK.

HPE 340: Exercise Biomechanics Refer to the diagram adapted from Lithorne (2001), and give each figure an ‘event name’ (left to right). Also name the four ‘phases’ which occur between each event, and name ‘critical elements’ occurring during each phase (i.e. knees straight, fingers pointed, etc.).

Adapted from; Lithorne, N. (2001). Analysis of standing vertical jumps using a force platform. Am J Phys, 69(11), 1198-1204.

Event name

Description

Stationary Starting Position.

Start of the jump in which athlete prepares themselves for the movement.

Max knee bend /lowest point

Legs are loaded - a preliminary downward movement by flexing at the knees and hips, Athletes crouches down lowering their COG towards the ground.

Last foot contact – start – toe off/takeoff

Legs extended  immediately and vigorously extends the knees and hips again to jump vertically up off the ground Last point of contact which the athletes has with the ground.

Peak of jump

Whilst athlete is in the air.

Landing / touchdown

Re contact with the ground.

References:Payton, C. J. & Bartlett, R. M. (2008). Biomechanical evaluation of movement in sport and exercise. Routledge, UK.

HPE 340: Exercise Biomechanics

Phase name

Critical elements

Loading Legs – Prep – squat

a preliminary downward movement by flexing at the knees and hips, Quant- Knee angle Qual- bend knees

Extension of the legs – Take off – Push/drive/push

 immediately and vigorously extends the knees and hips again to jump vertically up off the ground Quant-jump speed Qual- arm speed

Flight

 Distance between the floor and toes. Quant- height Qual – reach up

Decent

Small knee Flexion Small Hip flexion to absorb force upon impact. Quant- hip/ankle/knee flexion Qual- soft knees

References:Payton, C. J. & Bartlett, R. M. (2008). Biomechanical evaluation of movement in sport and exercise. Routledge, UK.

HPE 340: Exercise Biomechanics Practical Activity   

Set up the camera for analysis of the CMJ Capture three trials, aiming to jump as high as possible Review your trials. Are there any adjustments that need to be made for any additional trials?

With reference to the critical elements, identify five corrections you could suggest to the participant and describe how they influence performance Correction

Description

Phase Squat

Load the legs further

Phase Squat

Straighter back

Base of support

In line of line of gravity

Decent

Softer knees

References:Payton, C. J. & Bartlett, R. M. (2008). Biomechanical evaluation of movement in sport and exercise. Routledge, UK.

HPE 340: Exercise Biomechanics Consider the following recommendations for evaluation and intervention. Order of difficulty 

Attempt to fix easily modified errors first

Correct sequence 

When do movement errors occur?

Base of support 

Errors in lower body may affect trunk & upper body

Order your corrections from most important to least important and justify why. Correction

Justification

Bend knees

Soft landing

BOS

Straighter back

References:Payton, C. J. & Bartlett, R. M. (2008). Biomechanical evaluation of movement in sport and exercise. Routledge, UK.

HPE 340: Exercise Biomechanics Biomechanical Video Analysis Analysis space setup The space used for biomechanical analysis can have a major affect on the quality of the data captured during video analysis. The two major considerations for the space used are 1. Does the space allow the participant to reliably demonstrate the analysed movement, as would be performed in a typical environment? Considerations  

Is there adequate space for the movement to be performed? eg – sprinting, kicking, throwing Is the space a safe environment for the movement to be performed? eg – obstacles, floor surfaces, other individuals

2. Are the lighting conditions adequate for the capture of video data? Considerations    

Is there adequate light for the video camera to capture the movement? Are there excessive shadows within the capture field of view? Is the background colour consistent (preferably dark colour)? Is there excessive natural light in the background?

Considerations     

Is camera pointing perpendicularly to the desired plane of motion? Is the camera field of view oriented perpendicular to the horizontal and vertical of the lab space? Is the field of view the correct size to measure the desired variable? Is the camera at a maximum distance from the participant with the camera set to the maximum zoom possible? Will the desired measurements be captured as close to the centre of the field of view as possible?

References:Payton, C. J. & Bartlett, R. M. (2008). Biomechanical evaluation of movement in sport and exercise. Routledge, UK.

HPE 340: Exercise Biomechanics Positioning of the camera Biomechanical video analysis is described as 2D analysis as movements in only two linear degrees of freedom can be measured. That is, a camera measuring a long jumper in the sagittal plane can record the peak height and the length of the jump but cannot record the lateral displacement of the jumper in the pit. Positioning of the camera in the correct plane relative to the participant is vital for accurate biomechanical assessment. When positioning the camera in the lab space it must be ensured that the edges of the field of view are both horizontally and vertically perpendicular to the ground. Ensuring this orientation of the camera enables calculation of absolute joint angles and reduces the likelihood of the angles measured being distorted due to perspective error.

Figure 1

Angular distortion due to the camera being out of plane to the angle being measured.

By placing the camera as far from the participant as possible and applying the maximum optical zoom the accuracy of the measurements are enhanced due to the minimisation of errors referred to as parallax and perspective errors.

References:Payton, C. J. & Bartlett, R. M. (2008). Biomechanical evaluation of movement in sport and exercise. Routledge, UK.

HPE 340: Exercise Biomechanics Parallax errors As camera lenses are round, but produce a flat image, the linear distances recorded using video analysis become increasingly inaccurate as the measurement is made further and further from the centre of the field of view. That is distances away from the centre of the field of view appear shorter than at the centre.(See figure 2)

Figure 2 The discrepancies between the real position and camera measured position of joint centres relative to the centre of the field of view, due to parallax error.

References:Payton, C. J. & Bartlett, R. M. (2008). Biomechanical evaluation of movement in sport and exercise. Routledge, UK.

HPE 340: Exercise Biomechanics Perspective errors The distance of your participant to the camera will affect the relative size of his or her body in the field of view. Obviously someone standing close to a camera is going to look larger than a person standing a long distance from a camera. Therefore if you are trying to measure linear distances or displacements using video analysis, it is essential that the perspective of the camera is accurate.

A

Figure 3

B

A: Perspective error of two rods of identical lengths held at different distances from the camera B: The reduction of the perspective error due to the maximal optical zoom applied to the field of view

Figure 4

Visual depiction of the perspective error created by an object at different lengths from the camera

References:Payton, C. J. & Bartlett, R. M. (2008). Biomechanical evaluation of movement in sport and exercise. Routledge, UK.

HPE 340: Exercise Biomechanics Configuring the camera Digital video cameras have multiple settings that must be adjusted in accordance with the demands of the analysis being conducted. Frame rate Digital videos are essentially a series of still images placed in succession to one another and synchronised to the associated audio data. The number of images that are captured per second are referred to as the frame rate and are measured in Hertz (Hz) (frames per second). Standard Australian video cameras capture at 50 Hz but combine every two images captured into one to enhance the quality of the images and video is output at 25 Hz. Shutter speed Every image captured by the video camera involves the light entering the camera lens and being recorded for a very short period of time. This time can be adjusted and is referred to as the shutter speed. Due to the often rapid movements measured in biomechanics, a high shutter speed is required. Insufficient shutter speed during capture will result in blurring of the participant performing the movement. The shutter speed is measured by the amount of time that the camera records the image relative to one second. In biomechanics, shutter speeds of between 1/150 and 1/1000 are generally used. In general the fastest shutter speed should be used. Aperture Whereas the shutter speed concerns the time that each image captures the image at each frame, the aperture concerns the amount of light or the size that the camera shutter opens to during each frame. That is, the greater the opening of the shutter the more light and the brighter each frame will be. Biomechanical video analysis often requires large apertures to accommodate for the high shutter speeds used. ISO The ISO was originally a factor of the sensitivity of camera film to light. It is still used the same way in digital cameras but obviously there is no film. A higher ISO will produce a lighter image which is good for high speed video capture, although a high ISO also decreases the clarity of the captured video. Focus Manual focus must be used in biomechanical video analysis. As the auto focus function may not select the correct area of the field of view to focus on. For example if you are measuring a participant running through the field of view the camera will automatically focus on the background and then will not change the focus to the participant in time sufficient time during the period in which the participant is in the field of view.

References:Payton, C. J. & Bartlett, R. M. (2008). Biomechanical evaluation of movement in sport and exercise. Routledge, UK....