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motor neuron and all the muscle fibers that are innervated by that motor neuron
Typology: Lab Reports
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Background A motor unit is composed of a motor neuron and all the muscle fibers that are innervated by that motor neuron. In a persistent muscle contraction, multiple motor units are firing repetitively throughout the contraction of the muscle. The strength of a muscle contraction is related to the number of motor units in the muscle that are activated during the same time period. The electromyogram (EMG) recorded during the muscle contraction is seen as a burst of spike-like signals, and the duration of the burst is about equal to the duration of the muscle contraction. The strength of a striated muscle contraction is directly proportional to the amount of electrical activity in the muscle. However, it is difficult to quantify the amount of electrical activity in a muscle unless the raw EMG data is mathematically transformed. One of the most common transformations used is the integration of the absolute values of the amplitudes of the EMG spikes. Through this transformation, it has been found that the area under the graph of the absolute integral of the EMG is linearly proportional to the strength of the muscle contraction. In this experiment, students will use a hand dynamometer to measure a subject’s grip strength as the EMG activity of the forearm muscles used to generate the subject’s grip are recorded. The EMG activity will be related to the grip strength by plotting the maximum grip strength as a function the area under the absolute integral of the EMG activity during the muscle contraction. Data recordings will be made from the subject’s dominant and non-dominant forearms, and the relative strength and electrical activity of each forearm will be compared to its diameter. Recordings of prolonged grip strength and forearm EMG activity will also be made to determine the rate of fatigue in the dominant and non- dominant forearms. Equipment Required PC or Macintosh Computer IX-ELVIS USB cable Power supply Red, black, and green EMG leads Disposable electrodes FT-220 Hand dynamometer A-BT-220 Tubing GPSN-100 Pressure transducer Alcohol swabs Bathroom scale 5 or 6 textbooks or a 5-10 kg barbell weight String Metric ruler
IX-ELVIS Setup
Figure MP-1-S3: The EMG lead wires and the hand dynamometer assembly connected to an ETH/256.
Figure MP-1-S4: Placement of EMG electrodes on the forearm.
stronger than the first contraction.
Data Analysis
Table MP-1-L1: The Effect of EMG Activity on the Relative Muscle Strength in the Dominant Forearm. Dominant Forearm Diameter (mm):______ Relative Grip Strength Absolute Area of EMG Activity Absolute Area under Force Curve Lowest Higher 1 Higher 2 Highest Questions
Figure MP-1-6: The EMG (upper) and muscle force (lower) during a prolonged muscle contraction displayed in the Analysis window. The cursors are placed on the muscle force channel to measure the half-max fatigue time. Exercise 3: EMG Intensity and Force in the Non-Dominant Arm Aim: To determine the relationship between the intensity of EMG activity and the force of a muscle contraction in the subject’s non-dominant forearm. Procedure Follow the same directions used in Exercise 1 to record data from the subject’s non-dominant forearm. Data Analysis
Table MP-1-L2:The Effect of EMG Activity on the Relative Muscle Strength in the Non- Dominant Forearm. Non-Dominant Forearm Diameter (mm):______ Relative Grip Strength Absolute Area of EMG Activity Absolute Area under Force Curve Lowest Higher 1 Higher 2 Highest Questions Use the information from Exercises 1 and 3 to answer the following questions.