Biomechanical Instrumentation EMG Lab Purpose: The purpose of this lab is two-fold: 1) to introduce and familiarize the student with the necessary equipment needed to collect EMG data; and 2) to evaluate the effects of contraction velocity on the EMG activity of the biceps brachaii during an arm curl exercise. Rationale: Changes in the intensity of muscle contraction reflect many factors that may influence the demand that is placed on a muscle in a given situation. One of these factors is that involving the speed of contraction. It has been proposed that increases in the speed of contraction during a concentric contraction necessitate increases in the level of muscle activation. If this is the case, it would appear that such increases would be evident in the amplitude of associated EMG=s. Monitoring of the EMG levels during contractions of various speeds, then, should show variations in the amount of muscle activation. Methodology: 1. Examine and familiarize yourself with the equipment. 2. Prepare the preferred arm at the electrode site for electrode placement by cleaning the skin over the site. 3. Place electrodes over the muscle belly of the biceps brachaii & attach the reference electrode to a bony prominence on the arm/hand 4. Turn on the Noraxon receiver (switch on the back) and boot the laptop computer *Note - make sure that the power supply for the receiver is plugged into the outlet strip on the floor. 5. On the Computer choose "MyoResearch". A. Enter the appropriate project and patient information. B. Select” Measurement” from the menu and enter the appropriate Record name (i.e. name for the trial), and frequency (sampling rate). Designate the channel that you will be using. 6. Attach the electrode leads to the electrodes and turn on the transmitter. A. Select “Start” in the measurement window to begin the real-time display of the output of the muscle. 7. Perform a couple of contractions to make sure everything is working.....view the EMG on the computer screen to insure that the electrodes have been properly located A. On the display screen, “Store” begins saving the data and “Exit” end the data collection 8. Have the subject perform a Maximum Voluntary Contraction with the elbow at 90 degrees of flexion, against a fixed resistance. Collect and Save approximately six second of data during which this isometric is performed. 9. Have the subject perform three sets of six repetitions (moderate level of resistance) or arm curls, with data collection during each set. One set should be performed at a slow cadence (i.e. approximately six second per repetition), medium cadence (approx. four seconds per rep) and fast cadence (approx two seconds per rep). 10. After all three trials have been completed, rectify and smooth (50ms moving average) the data, then analyze three reps from each trial to calculate the average and peak EMG for each trial. Also rectify and process the MVC to determine the same parameters as above. 11. Normalize the average and the peak EMG values for the three trials using the results of the MVC analysis. Discussion: On the basis of a review of the data, respond to the following questions: #1 What were the Peak EMG and Average EMG values for each condition, and what do they represent? #2 How did the speed of the movement influence the Peak EMG.....the Average EMG? #3 Why do you think that speed influences how hard the muscle must work to complete a movement? #4 Do you believe that there is an "Optimum" speed of movement for maximum efficiency? If so/not, why? #5 What might some possible implications of your findings be for injury prevention ........for muscle strengthening? Note: The lab report should include a table with the Peak and Average EMG results for the three conditions.
Pages to are hidden for
"Applied Biomechanics - DOC"Please download to view full document