Skeletal Muscle Lab

Introduction

The most famous aspect of skeletal muscle is its ability to contract and ultimately create movement. Skeletal muscles are involved in both producing and stopping motion, like opposing gravity to sustain posture. To keep a body level or balanced in any and all positioning, subtle, continual changes of the skeletal muscles are performed. Veins abound in every skeletal muscle, supplying it with nutrients, oxygen, and waste export. Additionally, the axon branch of a somatic motor neuron serves every muscle fiber in skeletal muscle, signaling the fiber to contract or relax. Skeletal muscle can only move when it receives a signal from the nervous system, unlike cardiac and smooth muscle which move involuntarily.

In this lab, we will explore the protein make up of muscles as well as the different capabilities of muscle contractions, and ultimately what factors can affect muscle fibers and contraction. We will be measuring EMGs from muscle contraction and comparing muscle stimulation in different environments.

Equipment & Materials

• Shrimp
• Limes
• Cilantro
• Avocados
• Red Onions
• Roma tomatoes
• Hot sauce
• Chips
• Salt
• CAMRY Electronic Hand Dynamometer
• LabQuest 2 App
• Electrodes
• EKG/EMG Sensor
• Timer
• Measuring tape
• STIM Machine
• Squat Rack/Heavy weights
• Tandem Sport Vertical Challenger

Pre-Lab Questions

1. What is denaturing of proteins? What results from this process?

2. What does EMG stand for? What does it measure?

3. Describe the steps of a muscle contraction.

4. What is muscle fatigue? What is (or isn’t) happening in terms of contractions?

5. What is Post Activation Potentiation (PAP)?

Activity 1: Ceviche

Hypothesis: Acidic conditions will denature proteins just as effective as heat.

Place shrimp and/or fish in large mixing bowl. Add lime juice, lime zest, and salt, then toss to make sure shrimp is evenly coated. Set aside for 15 minutes (less and the shrimp won’t ‘cook’, more and the shrimp will become too tough). Every 5 minutes, take one piece of shrimp and cut it open to measure cooking. Record data in table 1 below. Meanwhile, add any other ingredients provided you would like in your ceviche. When the shrimp is done (you can test the doneness of the shrimp by taking a small piece and cutting it open – if it is opaque most of the way through, then it is considered done).

Shrimp Observations

Activity 2: Grip Strength & EMGs

Hypothesis: EMGs will increase with grip strength.

Acquire a CAMRY electronic hand dynamometer, LabQuest App with EKG sensors, and electrodes. Connect the EKG sensor into the LabQuest, then turn on the LabQuest. Choose ‘New’ from file menu. Place one electrode approximately 5 cm from your wrist and another 10 cm from your wrist. The third electrode can be placed on your bicep. Connect the green lead to the electrode closest to your wrist, the red lead on the adjacent electrode on your forearm, and the black lead on the electrode on your bicep. Using the stylus pen, follow these instructions to set up data collection on the LabQuest 2 App:

1. On the meter screen, tap sensors and then select sensor setup.
2. Tap the appropriate channel, scroll down the list of sensors, and tap Qubit.
3. Select q-S207 EKG/EMG and tap OK.
4. Tap OK again to return to the meter screen.
5. Change data-collection rate to 500 samples/s.
6. Zero the EKG sensor before collecting data.
7. Tap table and choose New Calculated Column from the Table menu.
8. Enter the Name (Column Rectified EMG or CR EMG) and Units (mV).
9. Select Aabs(X) as the Equation Type.
10. Select Potential for the Column for X.

Now, set up the hand dynamometer. Push the on button once to turn it on, then again to select gender and age. The middle two buttons (ARROWS up/down) allow you to select a different user. Then press (ON/SET) button to cycle between gender and age of the selected user, and edit the values using the arrows. When you are ready you can hit the (START) button to test your handgrip.

Once both the LabQuest and hand dynamometer have been set up, you are ready to begin data collection. Make sure your arm is resting comfortably on the table top. Using the same arm that is connected to EKG sensors, pull the CAMRY electronic hand dynamometer and begin data collection. Repeat this process an additional two times for a total of three attempts, then average the attempts and record below.

Participant Information

Force vs EMG

Average EMG:         mV

Activity 3: Muscle Fatigue in Dominant vs Non-dominant Arm

Hypothesis: Muscle fatigue will occur faster in subjects’ non-dominant arm.

Using your dominant hand on the electronic hand dynamometer, squeeze the trigger as hard as you can for as long as you can. Time how long it takes for the reading on the screen to hit 50% of the initial reading of force. Repeat this process an additional 2 times for a total of three, then average your time in seconds. Repeat this entire exercise with your non-dominant hand, and compare the results.

Dominant hand

Average:       s

Non-Dominant hand

Average:       s

Activity 4: STIM Machine Muscle Contraction

Hypothesis: Larger muscles (more muscle mass) will require less stimulation from the STIM machine in order to contract.

First, we will need to calculate our body fat percentage. Visit this link to calculate. You will need to input your age, weight, height, and neck and waist measurements. Click calculate; this is your body fat percentage. Take this percentage and subtract it from 100%; this is your lean mass. Now, convert your percentage into a decimal (move the decimal point two places to the left) and times it by your body weight. This is your lean body weight.

Lean body weight:            lbs

Sit or lay down on a table next to a STIM machine with your legs stretched out in front of you. Under the supervision of athletic trainers or Jaci, attach the 4 electrode pads to the 4 quadricep muscles on one leg. Attach the STIM machine connecters to the pads, ensuring the colors of the connectors are alternating with the red attachment starting closer to the knee. Turn on the STIM machine, and select Russian stimulation. Then, using the knob on the machine, slowly increase the amount of stimulation until your partner’s quad contracts.

**PLEASE START AT A SMALL NUMBER AND SLOWLY INCREASE – STARTING TOO HIGH OR GOING TOO FAST CAN RESULT IN CRAMP OR OTHER INJURY.

Record the number on the screen in the table below, and repeat these steps twice more. Average the recordings.

Stimulation of Quadriceps

Average stimulation needed for contraction:

Activity 5: Post Activation Potentiation (PAP) & Vertical Jump

Hypothesis: Students will increase their vertical jump after performing a heavy strength exercise in a gym.

Perform a vertical jump test 3 times, recording the height below and averaging all three attempts. Then, perform 3 squats at 85% of your 1RM (1 rep max) at the designated squat rack. Allow yourself to rest for 3-5 minutes, then attempt the vertical jump test 3 more times. Record your new attempts and average all three again. Record your data below.

Jump height (cm) before PAP

Rest time:       mins

Jump height (cm) after PAP

Post-Lab Questions

1. How did lime juice ‘cook’ the shrimp? Why would this only work on fish muscle (why do chicken and red meat not cook well this way)?

2. In our class data, did the force of grip strength correlate with the amount of EMGs present? Why is this important?

3. Did males or females have a higher grip strength? Did age play a part?

4. In our class, which hand fatigued faster: the dominant or non-dominant? Why is this important?

5. In our class data, did muscle mass have an effect on stimulation required for contraction?

6. What real world implications do muscle mass and STIM contraction have?

7. In our class data, were students able to jump higher after performing a heavy exercise? Why or why not?