Muscle 1: Grip Force

Muscle Activity (EMG) and Grip Strength

Aim

To determine the relationship between the EMG activity and the grip strength in your dominant arm.

Procedure

1. Sit quietly with your non-dominant forearm resting on the table top. This is the arm you do not use all the time.
2. You will squeeze the grip sensor five times, for two seconds each time with a two second rest between squeezes. Squeeze for 2 seconds and then let go for 2 seconds. Timing is important. Use only the finger tips when squeezing, do NOT use your whole fist. If you hold your thumb out (like you are hitchhiking) this will be easier.
3. Each squeeze will be a little stronger than the previous one.
• Squeeze 1 – very light.
• Squeeze 2 – a bit stronger.
• By the time you get to Squeeze 5 – it should be a really strong squeeze.

REMEMBER TO ONLY USE YOUR FINGER TIPS.

4. Once you understand what to do, click Record.
5. Squeeze five times as explained above. Click the AutoScale All button on the toolbar using your non-dominant hand.
6. After the last squeeze, click Stop.
7. Click File ---> Save As, name the file "Muscle-Grip", and save your data to your LabScribe Data folder on your Desktop.

Data Analysis

1. Click the "two mountain" icon once or twice to double the display time to show the whole recording on the screen.
2. Click the Analysis Window icon on the toolbar.

3. Click and drag the cursors to either side of the first EMG (muscle activity) burst. Abs. Int is the relative amount of the electrical activity causing the muscle activity and grip strength. Record the values for these in your table.

4. Repeat Steps 3 for the other four muscle contractions.
5. Click Save to save your data.

Put your data into a data table or into the Journal. You can open and close the Journal by clicking the "Notebook" icon.

Muscle Activity and Fatigue

Aim

To observe the relationship between the strength and length of contraction time of a muscle and EMG activity.

REMINDER – Do NOT use your whole fist – just use your fingertips when squeezing the bulb. Hold your thumb out.

Procedure

1. Click Record.
2. Squeeze the bulb and hard as you can. Use only your finger tips when squeezing, do not use the whole fist.
3. Hold the squeeze for as long as you can. You should try to hold for at least 1 minute, but no longer than 2 minutes.
4. Click the AutoScale button while recording.
5. Click Stop only after you let go of the bulb AND the your grip strength has dropped by at least 50% of the maximum squeeze at the beginning.
6. Click Save.

Data Analysis

1. Click the "two mountains" icon a few times until you have the whole recording of the Fatigue section on screen. You do not have to switch to the Analysis window unless you want to.
2. On the Muscle Force channel, drag one cursor to the flat line right before the big squeeze. Drag the other cursor to the peak of the big squeeze. Note the V2-V1 value on the Muscle Force channel. Write this in a data table or in the Journal. Open and close the Journal using the "Notebook" icon.
3. Keep the one cursor on the peak of the muscle force and move the cursor from the baseline to a point on the force channel where the value of V2-V1 is 50% of the full grip strength. Note – this number will be negative.
• Example: if your force was 15 PSI at the beginning, then half (50%) of that would be 7.5 PSI
4. Look at T2-T1, this is the time it took for the muscle to get to 50% of it's original, full strength.

Answer the following:

Exercise 1

1. Using Excel or another graphing program, plot the absolute integral of muscle contraction as a function of the absolute integral of the EMG signals for each muscle clinch. EMG will be the X-axis and Muscle Force will be the Y-axis. Plot a “line of best fit” on the graph (do NOT connect the dots).
2. Is there a linear relationship between the muscle activity (EMG) and the grip strength (force)? How does the muscle force relate to the EMG activity?
3. Do muscle fibers have a refractory period like nerve fibers?