Lab 4: Contractility and Fatigue of Skeletal Muscle Flashcards
What is the objective of this lab?
to observe and measure the muscle contraction and to understand the effects of fatigue on muscle strength
What is a motor unit composed of?
a motor neuron and all the muscle fibres that are innervated by that motor unit
In a persistent muscle contraction…
multiple motor units are firing repetitively throughout the contraction
What is the strength of a muscle contraction related to?
The number of motor units in the muscle that are activated during the same period of time
What does the EMG look like during the muscle contraction period?
a burst of spike like signals where the burst is 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
Since it is difficult to quantify the amount of electrical activity in a muscle you have to mathematically transform the raw EMG data. How can you transform this data?
by integrating the absolute values of the amplitude of the EMG spikes.
What does the transformation of the EMG data tell you?
the area under the graph of the absolute integral of the EMG is linearly proportional to the strength of the muscle contraction.
How does the EMG activity relate to the grip strength in this lab?
by plotting the max grip strength as a function and the area under the absolute integral of the EMG activity during the muscle contraction
Which forearm is being recorded for this experiment?
the subject’s dominant and non-dominant forearm
Which device is used to measure the subject’s grip strength?
a hand dynamometer
What additional results can be obtained from the recording of the grip strength and EMG activity?
the rate of fatigue in the forearms
Equipment required:
-laptop
-black iWork case:
~IXTA-ROAM unit
~C-AAMI-504 ECG cable and electrode lead wires
-disposable electrodes
-FT-220 Hand Dynamometer
-bathroom scales and large pail (5-10L)
-string
-metric ruler
Follow IXTA-ROAM setup with adding…
-plug the connector to FT-220 hand dynamometer into the A2 input of IXTA-ROAM
-plug the iWire 3BG electrode harness connector into the iWire 1 plug in the IXTA-ROAM
-connect the red, black and green lead electrode wires to the electrodes
Subject setup:
- place the red wire near the elbow
- place the black wire in the middle of the forearm
- place the green wire on the wrist
Once you open LabScribe23 what file are you opening?
-pull down settings, select Human Muscle Folder and click the setting file “EMG-GripStrength-iWireB3G”
Is a calibration required? If so for what piece of equipment?
yes, for the hand dynamometer
What do you use to calibrate the hand dynamometer?
a pail with water
What are the steps for calibrating
- collect a pail of water and weigh it and record it in kg
- Place the hand dynamometer on the bench and click record
- Place the pail of water on the bulb and record for an additional. 10 sec and then click stop recording
- Click auto scale and the double cursor button
- Open the channel menu of the muscle force channel by clicking on the down arrow to the left of the channels title. Select Units from this menu and Simple from the submenu to open the Simple Units Conversion window
- When this window appears select the following:
~2 point calibration
~apply units to new data
~apply units to all blocks
~Cursor 1: 0 in the box on the right, for the portion of the recording when no weight was placed on top of the hand dynamometer
~Cursor 2: the weight of the pail and water in the box on the right
~Unit name: kg
Exercise 1: EMG Intensity and Force in DOMINANT Arm
What is the goal of this experiment?
to determine the relationship between the intensity of EMG activity and the form of the muscle contraction in the subject’s dominant arm
Exercise 1: EMG Intensity and Force in DOMINANT Arm
Procedure
- Have the subject sit quietly with their forearm rested on the bench top and explain that they will squeeze their fist around the hand dynamometer 4 times, each contraction2 seconds long followed by 2 seconds of relaxation (each successive contraction should be approx. 2,3,4 times stronger than the first contraction
- When the subject is ready to start, put the correct title in the mark box and start recording
- Once completed click the stop button
- Click autoscale and save the file
Exercise 1: EMG Intensity and Force in DOMINANT Arm
Analysis
- Use the Double Cursor to select the beginning and the end of the contraction
- Click on the analysis icon in the tool bar to observe the results
- The values Abs.Int, V2-V1 and T2-T1 will be shown and can be saved in the journal
What is the metric ruler used for?
To measure the circumference of their forearm 3cm below the elbow
Do muscles have a refractory period like nerve fibers?
No muscle fibers do not have a refractory period like nerve fibres. Instead they have something called a latent period
since they dont have. a refractory period, the action potentialsare able to be summed, allowing for greater out put (called rate codin)
What is a refractory period?
a brief period after action potential occurs where nerves are temporarily unable to generate another action potential
What is a latent period?
when the muscle is still in the process of transitioning from excitation to contraction, and no visible movement occurs.
Is there a linear relationship between absolute integral under EMG signals and the absolute integral under the muscle contraction?
yes
Exercise 1: EMG Intensity and Force in DOMINANT Arm
Expected results
-as grip strength increase, absolute int. of EMG activity increases as well as absolute int. under force curve
Exercise 2: EMG Intensity and Fatigue in DOMINANT Arm
What is the goal of this experiment?
to observe the relationship between the length and strength of a muscle contraction and EMG activity in the dominant forearms
Exercise 2: EMG Intensity and Fatigue in DOMINANT Arm
Procedure
- Have the subject sit with their hand resets on the bench top
- Instruct the subject to: squeeze the bulb of the hand dynamometer as tightly as they can for as long as they can to attempt to fatigue the muscle
- Stop the recording once the subject’s strength drops to half of the subjects max muscle force from the beginning of the recording (approx. 20 sec)
- Start another recording for a baseline of 10 seconds then instruct the subject to squeeze the bulb with as much force as possible
- Click autoscale for EMG and Muscle Force Channel
- When the subject’s muscle strength decreases to a level that s 50% below the max muscle strength at the beginning, instruct the subject to stop squeezing the bulb and stop recording
- Save the file in the appropriate place
What will happen to the subjects forearm as time passes?
as the time passes the subjects force will decrease at a rate dependant on the fitness level of the subject
Exercise 2: EMG Intensity and Fatigue in DOMINANT Arm
Analysis
- look at the values Abs.Int, V2-V1 (the amplitude) and T2-T1
-using 2 cursors, place one at the baseline before the muscle contraction and the second at the peak muscle force near the beginning of the contraction
-the half max muscle force (divide the max muscle force by 2)
-the half max fatigue time is the time it takes the muscle force to decrease to 50% of the max during the fatigue experiement. Place one cursor on the peak muscle force and the second to the right of the peak muscle force until the absolute value for V2-V1 is equal to the half-max muscle force.
Exercise 3: EMG Intensity and Force in the NON-DOMINANT
What is the goal?
to determine the relationship between the intensity of EMG activity and the force of a muscle contraction in the subject’s non-dominant forearm
Exercise 3: EMG Intensity and Force in the NON-DOMINANT
Procedure
-follow the procedure from exercise 1 where you have to squeeze the bulb at different strengths
Exercise 3: EMG Intensity and Force in the NON-DOMINANT
Results
-the Abs. Int of EMG Activity and Abs. Int under force cure were both lower than the dominant are but also both increase as strength increase
Exercise 4: EMG Intensity and Fatigue in NON-DOMINANT Arm
What is the goal
to observe the relationship between strength of a muscle contraction and EMG activity in the non dominant forearm
Exercise 4: EMG Intensity and Fatigue in NON-DOMINANT Arm
Procedure
follow the procedure for exercise 3 where you squeeze the bulb the hardest you can
Exercise 4: EMG Intensity and Fatigue in NON-DOMINANT Arm
Analysis
weaker than dominant arm
Is there a relation between circumference of the forearm and max force?
no there’s no correlation
How to calculate perfect difference
|a-b|
——– x 100%
a+b/2
