Lab 4: Contractility and Fatigue of Skeletal Muscle

Question 1

What is the objective of this lab?

Answer 1

to observe and measure the muscle contraction and to understand the effects of fatigue on muscle strength

Question 2

What is a motor unit composed of?

Answer 2

a motor neuron and all the muscle fibres that are innervated by that motor unit

Question 3

In a persistent muscle contraction…

Answer 3

multiple motor units are firing repetitively throughout the contraction

Question 4

What is the strength of a muscle contraction related to?

Answer 4

The number of motor units in the muscle that are activated during the same period of time

Question 5

What does the EMG look like during the muscle contraction period?

Answer 5

a burst of spike like signals where the burst is equal to the duration of the muscle contraction

Question 6

The strength of a striated muscle contraction is directly proportional to…

Answer 6

the amount of electrical activity in the muscle

Question 7

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?

Answer 7

by integrating the absolute values of the amplitude of the EMG spikes.

Question 8

What does the transformation of the EMG data tell you?

Answer 8

the area under the graph of the absolute integral of the EMG is linearly proportional to the strength of the muscle contraction.

Question 9

How does the EMG activity relate to the grip strength in this lab?

Answer 9

by plotting the max grip strength as a function and the area under the absolute integral of the EMG activity during the muscle contraction

Question 10

Which forearm is being recorded for this experiment?

Answer 10

the subject’s dominant and non-dominant forearm

Question 11

Which device is used to measure the subject’s grip strength?

Answer 11

a hand dynamometer

Question 12

What additional results can be obtained from the recording of the grip strength and EMG activity?

Answer 12

the rate of fatigue in the forearms

Question 13

Equipment required:

Answer 13

-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

Question 14

Follow IXTA-ROAM setup with adding…

Answer 14

-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

Question 15

Subject setup:

Answer 15

• place the red wire near the elbow
• place the black wire in the middle of the forearm
• place the green wire on the wrist

Question 16

Once you open LabScribe23 what file are you opening?

Answer 16

-pull down settings, select Human Muscle Folder and click the setting file “EMG-GripStrength-iWireB3G”

Question 17

Is a calibration required? If so for what piece of equipment?

Answer 17

yes, for the hand dynamometer

Question 18

What do you use to calibrate the hand dynamometer?

Answer 18

a pail with water

Question 19

What are the steps for calibrating

Answer 19

1. collect a pail of water and weigh it and record it in kg
2. Place the hand dynamometer on the bench and click record
3. Place the pail of water on the bulb and record for an additional. 10 sec and then click stop recording
4. Click auto scale and the double cursor button
5. 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
6. 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

Question 20

Exercise 1: EMG Intensity and Force in DOMINANT Arm
What is the goal of this experiment?

Answer 20

to determine the relationship between the intensity of EMG activity and the form of the muscle contraction in the subject’s dominant arm

Question 21

Exercise 1: EMG Intensity and Force in DOMINANT Arm
Procedure

Answer 21

1. 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
2. When the subject is ready to start, put the correct title in the mark box and start recording
3. Once completed click the stop button
4. Click autoscale and save the file

Question 22

Exercise 1: EMG Intensity and Force in DOMINANT Arm
Analysis

Answer 22

1. Use the Double Cursor to select the beginning and the end of the contraction
2. Click on the analysis icon in the tool bar to observe the results
3. The values Abs.Int, V2-V1 and T2-T1 will be shown and can be saved in the journal

Question 23

What is the metric ruler used for?

Answer 23

To measure the circumference of their forearm 3cm below the elbow

Question 24

Do muscles have a refractory period like nerve fibers?

Answer 24

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)

Question 25

What is a refractory period?

Answer 25

a brief period after action potential occurs where nerves are temporarily unable to generate another action potential

Question 26

What is a latent period?

Answer 26

when the muscle is still in the process of transitioning from excitation to contraction, and no visible movement occurs.

Question 27

Is there a linear relationship between absolute integral under EMG signals and the absolute integral under the muscle contraction?

Answer 27

yes

Question 28

Exercise 1: EMG Intensity and Force in DOMINANT Arm Expected results

Answer 28

-as grip strength increase, absolute int. of EMG activity increases as well as absolute int. under force curve

Question 29

Exercise 2: EMG Intensity and Fatigue in DOMINANT Arm What is the goal of this experiment?

Answer 29

to observe the relationship between the length and strength of a muscle contraction and EMG activity in the dominant forearms

Question 30

Exercise 2: EMG Intensity and Fatigue in DOMINANT Arm Procedure

Answer 30

1. Have the subject sit with their hand resets on the bench top 2. 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 3. 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) 4. Start another recording for a baseline of 10 seconds then instruct the subject to squeeze the bulb with as much force as possible 5. Click autoscale for EMG and Muscle Force Channel 6. 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 7. Save the file in the appropriate place

Question 31

What will happen to the subjects forearm as time passes?

Answer 31

as the time passes the subjects force will decrease at a rate dependant on the fitness level of the subject

Question 32

Exercise 2: EMG Intensity and Fatigue in DOMINANT Arm Analysis

Answer 32

- 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.

Question 33

Exercise 3: EMG Intensity and Force in the NON-DOMINANT What is the goal?

Answer 33

to determine the relationship between the intensity of EMG activity and the force of a muscle contraction in the subject's non-dominant forearm

Question 34

Exercise 3: EMG Intensity and Force in the NON-DOMINANT Procedure

Answer 34

-follow the procedure from exercise 1 where you have to squeeze the bulb at different strengths

Question 35

Exercise 3: EMG Intensity and Force in the NON-DOMINANT Results

Answer 35

-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

Question 36

Exercise 4: EMG Intensity and Fatigue in NON-DOMINANT Arm What is the goal

Answer 36

to observe the relationship between strength of a muscle contraction and EMG activity in the non dominant forearm

Question 37

Exercise 4: EMG Intensity and Fatigue in NON-DOMINANT Arm Procedure

Answer 37

follow the procedure for exercise 3 where you squeeze the bulb the hardest you can

Question 38

Exercise 4: EMG Intensity and Fatigue in NON-DOMINANT Arm Analysis

Answer 38

weaker than dominant arm

Question 39

Is there a relation between circumference of the forearm and max force?

Answer 39

no there's no correlation

Question 40

How to calculate perfect difference

Answer 40

|a-b| -------- x 100% a+b/2