BIOMEDICAL INSTRUMENTATION

HUMAN SYSTEMS LAB

ELECTROMYOGRAPHY (EMG)

LEARNING OBJECTIVES:

By the end of this experiment, the student should be able to:

• Attach the electrodes for conducting this experiment.

• Locate median nerve by using stimulator bar electrode.

• Record EMG responses evoked by stimulating the median nerve at the wrist.

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Electromyography Electromyography (EMG) is a diagnostic procedure that evaluates nerve or muscle problems by measuring electrical activity of muscles, surface or needle electrodes are needed for this. EMG is performed if there are symptoms as (tingling, muscle weakness, involuntary muscle twitching, numbness, paralysis, muscle pain and cramping). For getting ready for EMG ideally wear comfortable clothing so that needed area can be exposed easily, don’t smoke for at least three hours before, remove any oils from the skin, don’t apply any lotions, during EMG two type of studies will be performed ideally nerve conduction study (for evaluation of motor neurons by using electrodes) and needle electrode (for evaluation of muscles’ electrical activity) and it should take almost 30 and 60 minutes. But we have done the procedure by using surface disposable electrodes and have noted the EMG while voluntary contraction of biceps, lift loading and stimulation of median nerve and record muscle activity from the Abductor pollicis brevis muscle

OBJECTIVE:

The objective is to evaluate the muscle activity first by voluntary contraction

and relaxation of bicep muscle after that by applying load and checking the

difference in contraction intensity and to sort out the co activation of biceps

and triceps and finally to stimulate the median nerve at the wrist and on

elbow and record muscle activity from the Abductor pollicis brevis (a thumb

muscle).

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REQUIREMENTS:

The requirements for performing the practical are:

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The requirements include Lab tutor, electrodes, lubricating gel, human volunteer and stimulator.

STUDY QUESTIONS:

Exercise 1: Voluntary Contraction

EMG Amplitude

Books Amplitude 0 0.06 1 0.04 2 0.11 3 0.11 4 0.12

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Study Questions 1. Unlike the discrete waveform from an electrocardiogram, the electromyogram waveform is irregular. Why do you suppose this is?

As the electromyogram measures electrical activity of skeletal muscles and skeletal muscles don’t have the ability to so contractions in complete synchronized fashion while the cardiac muscle is a smooth muscle and can contract in complete synchronizes fashion that’s why discrete waveform is found in ECG but not in EMG. , 2. In your own words, explain how the EMG trace changed when you added weights to your arm? Based on the data you collected what can you infer is happening to the muscles as weight is added?

The EMG trace changes as we add weights on the arm as because of load the contraction of the muscle get increased to support the extra weight also and as we go on increasing the weight on the same muscle the contraction and tension of the muscle also increases now but the level of contraction is less as compared to that attained after applying the first load.

Exercise 2: Alternating activity and coactivation

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EMG Amplitude

Condition Biceps Triceps

relaxation 0.13 0.66

contraction 0.58 0.3

Study Questions 3. In your own words what is coactivation? What are some explanations you can come up with for this phenomenon?

Co activation is the mild contraction of antagonist muscle as a result of contraction on agonist muscle as for example triceps and bicep muscles. In our experiment we have done contraction on bicep and the value of contraction was found to be 0.58 and while this anatogist the tricep also contracted to a weaker extent and the value was 0.3. 4. Coactivation of abdominal muscle and muscles supporting the spine has been shown to be essential for the bipedal posture of humans. Based on your data, is the coactivation of the triceps necessary for proper functioning of the biceps and vice versa?

Yes, as abdominal and spinal muscles support each other and maintain the posture, bicep and triceps muscles also support each other and work in a fashion to oppose each other (antagonist), as the opposing forces balance each other so help in maintaining the stability and proper functioning. We have done contraction at bicep and the value got 0.58 and as a result relaxation at triceps was found and the value was 0.66

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Exercises 3 & 4: Evoked EMG & nerve conduction velocity

Evoked EMG

Wrist Latency (s) Elbow Latency (s) Distance (mm) Velocity (m/s)

0.0038 0.0095 245 63.2

Study Questions 1. List the physiological events that occur between delivery of the stimulus and the start of the recorded response (i.e. during the latent period).

There are two events that occur between delivery of stimulus and start of recorded response are:

1. Atrial Repolarization 2. Ventricular Depolarization

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2. Which of the contributions to the latent period (that you listed in question 1 above) depends on the position of the stimulating electrode?

The distance from Central nervous will be the main factor, as the distance increases it will take longer to deliver the message, because the message have to pass the way through Peripheral nervous system to central nervous system and after completion of message cycle the muscle fiber connected to the electrode react.

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3. Based on your results and calculations for nerve conduction velocity, how long would it take for a nerve impulse to travel from the spinal cord to the big toe? Assume that the distance traveled is one meter.

The time nerve impulse would take to travel from spinal cord to big toe in the distance of 1 meter is 0.0163sec.

4. Was there variability in the nerve conduction velocity amongst members of your group? What are some explanations for this?

There is variability in nerve conduction velocity among individuals and is dependent on body properties of the subject as body’s height and body’s temperature.

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