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 i nformation 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 wir e 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 (Ω). ‐ 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 com puter 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 ergom eter is not cri tic al 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 cli ck on the start “button” in the lower right hand corner of the screen. Data will be collect ed 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 collectio n 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 cli ck 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 Exce l, 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