UMass Amherst KIN 430 - BiomechLabD (4 pages)

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BiomechLabD



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BiomechLabD

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Pages:
4
School:
University of Massachusetts Amherst
Course:
Kin 430 - Biomechanics
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Biomechanics Laboratory D Angular Kinematics Introduction The purpose of this laboratory is for students to become familiar with collecting analyzing and interpreting angular kinematic data Knee joint angular data will be collected using an electro goniometer placed about the knee as subjects pedal on a Monark cycling ergometer using two different cadences The goniometer will provide information on instantaneous knee joint angles angular positions from which angular velocities and accelerations will be derived From these data knee joint kinematics between two pedaling rates will be compared and contrasted Methods Participants At each workstation a group of 3 4 students will work together to record knee joint kinematics during pedaling All of the students in a group will take turns pedaling and performing the other duties related to data collection What you need for this lab Bring a USB flash drive aka a memory stick thumb drive etc Be dressed in shorts or loose pants that can be rolled up above the knee All students will participate except in extenuating circumstance recent leg injury allergic to adhesive etc Instrumentation Electro goniometer Simply a goniometer is a device that measures angles In this lab we will use an electro goniometer to measure knee joint angles during pedaling We will only measure the knee angle in the sagittal plane flexion extension however angles can be measured in other planes if desired The goniometer contains a composite wire inside a protective spring between the two endblocks The voltage signal from the goniometer is proportional to the strain change in shape of the wire As the angle between the two ends changes the strain in the wire changes as does the output signal from the goniometer which can be equated to the joint angle Care must be taken when handling and using the electro goniometer as mishandling may result in inaccurate data reduced equipment life or equipment failure Please heed the following Never remove the goniometer from the subject by pulling on the cable and or protective spring Remove carefully by the endblocks one at a time Take care when mounting goniometers to ensure that the measurement element always forms a simple bend shape or C not an omega Do not pull the goniometer to its extreme length The rate or frequency at which data are collected from the goniometer data is preset at 20 Hz i e 20 samples per second Procedures Steps for data collection 1 Designate a participant a computer operator and an RPM watcher The participant will pedal on the ergometer for one trial at each of two cadences first at 40 RPM then at 80 RPM The computer operator will collect the data and the RPM watcher will alert the computer operator when the participant has reached and sustained the desired pedaling rate The resistance on the ergometer is not critical for this experiment and can be set to any comfortable moderate intensity 2 With the participant seated on the ergometer carefully attach the goniometer on the left leg of the participant Attach one double sided sticky tape piece to each endblock With the knee joint fully extended affix the goniometer so that it is on the lateral aspect of the leg see picture left leg shown Be careful to not stretch the spring to its maximum length but do apply some tension along the length of the goniometer as you are placing it on the limb 3 The participant will then start pedaling Once 40 RPM is reached the RPM watcher will inform the computer operator who will then click on the start button in the lower right hand corner of the screen Data will be collected for 5 s The participant will need to pedal as consistently as possible for those 5 seconds When collection has ended the trace on the computer screen will stop scrolling 4 Once the first 5 second data collection is finished the watcher can then inform the participant to increase to 80 rpm When the pedaling rate is consistently 80 rpm the RPM watcher will inform the computer operator who will then click the start button Again data will be collected for 5 seconds It is important that the participant pedals for the full 5 seconds during each of the two trials 5 After both trials have been collected save the data to the participant s thumb drive by using the drop down file menu save as Export it as a txt file naming it ParticipantsInitials LabD LabSection txt example JDS LABD 01 txt This data will be analyzed as described later 6 ONCE THE DATA ARE SAVED close out the BIOPAC window then reopen BIOPAC in the upper left corner on the desktop In the separate window that opens under the BSL PRO tab double click on 430 LABD to prepare the computer for the next participant Repeat steps 1 6 until each student in your group has his or her own data Be sure to rotate though the responsibilities within the group Assignment For this assignment you will compare and contrast the angular positions velocities and accelerations between the two pedaling rates 40 rpm and 80 rpm using Excel for data analysis and for creating graphs Make sure that you understand how to perform the necessary analyses and how to generate the necessary graphs in Excel before leaving the lab 1 To prepare your data in Excel follow these steps a open your data file in Excel b in the first column create a time column based on the sampling rate used to collect the data c move the data for 80 RPM to a new column 0 5 seconds are the data for 40 RPM and 5 10 seconds are the data for 80 RPM and d add titles for your columns to help you remember which column is which i e column titles could be Time 40 RPM position 80 RPM position etc 2 Experimental data can be contaminated with high frequency noise that gets amplified when you differentiate the data To minimize the noise in the angular position data we can smooth the data using a moving average For data points 2 through N 1 calculate a 3 point moving average by summing 3 consecutive values and then dividing the result by 3 Equation 1 For the first data point and the last data point you will need to use a simple 2 point average This will create a new column of smoothed angular position data in Excel for each of the two pedaling cadences 1 3 Using Excel determine angular velocity by differentiating the smoothed angular position data with respect to time then determine angular acceleration by differentiating the angular velocity data with respect to time do this for both pedaling rates 4 Create three graphs angular position v time angular velocity v time


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