1) Determine the maximum clench strength for right and left hands and compare differences between male and female.
2) Observe, record, and correlate motor unit recruitment with increased power of skeletal muscle contraction.
3) Record the force produced by clench muscles, EMG, and integrated EMG when inducing fatigue.
Procedure
- Subject preparation. Clean the skin with rubbing alcohol to make sure the gel electrodes remain adhered to the skin securely during the EMG recording time. Place gel electrodes on your dominant arm and set up the lead/cable connection by following Figure 1. The cable should be plugged in Channel 1 (“CH 1”) of the Biopac data acquisition module, Figure 2. Turn on Biopac MP36; double click “BIOPAC BSL4.0 MP36” to open up the software; select “Record or Analyze a BIOPAC Lesson” and “L02 - Electromyography (EMG) II”, and “OK”.
Figure 1 Electrode placement and lead attachment (dominant arm first and then non-dominant)
Figure 2 Cable, dynamometer, and headphone plug in CH1, CH2, and OUT1 of Biopac MP36, respectively.
- Calibration.
1) Click “Calibrate”. Set the hand dynamometer down and click OK. Grasp the dynamometer with your hand in the way shown in Figure 3 and then click OK.
2) When Calibration recording begins, clench the hand dynamometer as hard as possible for 2 sec. and then release. Wait for Calibration to stop.
3) Check the Calibration data, which should look similar to Figure 4. If the recording does not have a zero (flat) baseline, repeat calibration to match Figure 4.
Figure 3 Clench dynamometer for Calibration
(Place the short grip bar against the palm, toward the thumb, and wrap your fingers to center the force.)
Figure 4 Dynamometer calibration curve
- Data recording.
You will record two segments on each forearm:
a. Segments 1 and 3 record Motor Unit Recruitment - Increasing clench force
b. Segments 2 and 4 record Fatigue - Continued clench at maximum force
Overall, your data should look like Figure 5, with integrated EMG recorded in the upper channel (CH 40) and the clench force the lower (CH 41). Dominant arm: Motor Unit Recruitment - Increasing clench force
a) Click Continue. When you click Continue, the display will change to show only the Clench Force channel, with grids on and the grid division scale based on your assigned increment so that you can visually review the increment levels.
Figure 5 EMG II data recording
b) Based on your calibrated grip force, the software determines the optimal grid display and assigns force increments. If the grid display looks like Figure 6, it means that the force increments are 20 kg.
c) Subject performs/repeats Clench-Release-Wait cycles with increasing clench force, holding for two seconds and waiting for two seconds after releasing before beginning the next cycle. Begin with your assigned increment and increase each successive cycle by the assigned increment until maximum is reached.
d) Click Suspend. Review the data on the screen.
Figure 6 Motor unit recruitment. Clench, Release, Wait, Repeat (4 times) with 20 kg as increments.
Dominant arm: Fatigue - Continued clench at maximum force
1) Click Continue. Click Resume.
2) Clench the dynamometer with your maximum force and try to maintain it.
3) When the maximum clench force displayed on the screen has decreased by more than 50%, click Suspend. If data looks similar to Figure 6, continue.
Figure 7 Fatigue - clench at maximum force until 50% decrease
Non-dominant arm: Motor Unit Recruitment - Increasing clench force
1) Prepare the other arm the same way as the dominant arm and repeat the procedure mentioned above.
2) Data should look similar to Figure 6, except that the height of each plateau (the strength) is smaller.
Non-dominant arm: Fatigue - Continued clench at maximum force
4) Data should look similar to Figure 7.
- Data analysis
Enter the Review Saved Data mode and choose the correct file and open it. Again, your data should look like Figure 5. Channel designations and measurement box settings are shown in Figure 8.
Figure 8 Channel designations and measurement box settings
1) Analysis of Motor Unit Recruitment - Increasing clench force
a) Setup your display for optimal viewing of the “Forearm 1, Increasing clench force” segment data.
b) Use the I-Beam cursor to select an area on the plateau phase of the first clench, Figure 9.
c) The values obtained from CH 41 Mean and CH 40 Mean represent Force (in kg) and Integrated EMG (in mV) to be entered in Table 1 for Clench #1.
d) Do the same for the rest of the clenches.
e) Do the same for the non-dominant arm with “Forearm 2, Increasing clench force”.
2) Analysis of Fatigue - Continued clench at maximum force
a) Scroll to “Forearm 1: Continued clench at maximum force” segment and set up your display for optimal viewing.
b) Find the maximum clench force by using the I-Beam cursor to select the peak point immediately following the start of the segment (the maximum value displayed in CH 41 Value), as shown in Figure 10. This maximum clench force value is to be entered in Table 2 for the Dominant arm.
Figure 9 Plateau of first clench selected
Figure 10 Maximum clench force selection
c) Calculate 50% of the maximum clench and enter the value in the box under 50% of Maximum Clench Force (calculated) in Table 2.
d) Locate the approximation of the point that is 50% down from the maximum clench point on the clench force curve by using this calculated 50% of the maximum clench as reference.
e) Select the area from the point of 50% clench force back to the point of maximum clench force by using the I-beam cursor and dragging (Figure 11). The time to fatigue measurement is displayed in CH 40 Delta T, which is to be entered in the box under Time to Fatigue in Table 2.
f) Repeat the above procedures to obtain the data for Non-dominant arm, complete Table 2.
- Is the strength of your right arm different than your left arm? (3 pts) ____Yes No
- Is there a difference in the absolute values of force generated by males and females in your group/class? (3 pts) ____Yes ____No
What might explain any difference? (12 pts) - When holding an object, does the number of motor units remain the same? Are the same motor units used for the duration of holding the object? (10 pts)
- As you fatigue, the force exerted by your muscles decreases. What physiological processes explain the decline in strength? (10 pts)
- Define Motor unit (6 pts)
- Define Motor unit recruitment (6 pts)
- Define Dynamometry (10 pts)