Lab: Muscle Function
Purpose: To determine the relationship between stimuli and fatigue in skeletal muscles.
Background: Do you ever exercise to a point where you experience fatigue? Within muscle cells, fatigue is a temporary loss of
ability to respond to stimuli. Fatigue occurs when the energy supply to the muscle cells has been depleted and waste
products have accumulated. During moderate exercise, the blood supplies enough oxygen from inhaled air to provide the
muscles with energy. This is known as aerobic exercise. Well-conditioned marathon runners pace themselves so that
their body’s need for oxygen is about equivalent to the amount of air they inhale. Athletes that play sports that require
intense, anaerobic exertion, such as weightlifters, draw on sources of energy that do no depend on inhaled oxygen. Proper
exercise improves aerobic capacity of the cardiovascular system and decreases the chance of developing cardiovascular
disease.
Materials: Timer (clock with seconds hand), laboratory tubing or large rubber band, weights, beaker, ice, pencil
Procedures:
Part A:
1. Read the following procedure and then, write a hypothesis about what will happen to the major muscles in your upper
arm (biceps and triceps) during this lab.
2. Stretch one arm in front of you and open your hand. Now place your other hand around the upper half of your extended
arm. Make a fist and tightly bend (flex) your extended arm.
3. Describe the changes you feel as you bend your arm.
4. Generate several hypotheses about what conditions would make your arm muscles tire quickly.
**As you do each part of the investigation, your partner will be the timekeeper and recorder. Then you will reverse roles and
become the timekeeper and recorder for your partner**
Part B: Continual Muscle Stimulation: To gather data about muscle fatigue hold your arm straight in front of you at a 90°
angle. With palm turned up, open and close your hand into a fist (flexing) as many times as possible in 20 seconds. Keep your
arm out. Without resting between trials repeat this procedure 10 times total.
5. How do you think the feeling in your arm and hand will change as you progress through your trials? Record data while your
partner performs Step B.
6. Your partner will record your counts on your data chart. Average the counts from your 10 trials and enter average on
your data chart.
Part C: Restricted Blood Flow: To investigate how blood supply affects muscle function.
7. Have your partner tie a piece of laboratory tubing snugly around your upper arm. Note: Be sure not to tie too tightly; you
should be able to fit one finger under the rubber tube. You will perform 10 trials of the hand-flexing exercise for 20
seconds, as in Step B.
8. Record the numbers of times for each trial on the data chart and then enter your average.
9. Record data while your partner performs Part C.
Part D: Weight Lifting: To investigate the effect of weight on muscle function, you will test how long you can hold a weight
before you arm becomes tired.
10. Predict which arm will tire first. Explain your choice.
11. Hold one weight in each hand. Keep one arm straight by your side and extend the other arm as in Step B. Hold this
position as long as you can. Repeat this action extending your other arm.
12. How long does it take for each arm to become tired? Explain your results.
Part E: Varying Temperature: You will examine how temperature influences muscle activity.
13. Write your full name three times on a piece of paper.
14. Do you think your ability to write your name will be affected by how warm or cold your hand is? Give reasons for your
answer.
15. Now tightly hold several ice cubes in your hand for one minute. Quickly drop the ice cubes into the beaker.
16. Immediately write your full name three times. Do not dry your hand before writing. Note: Use pencil; the water will
make the ink run.
17. Warm your hands by rubbing them together.
18. Write your full name again three times.
19. Look at all your signatures. How did the different temperature treatments affect your ability to write?
Name:___________________________________________________________________________ Date:_________________________ Period:____________
Lab: Muscle Function
Data:
Part of Lab
A: Control
Hypothesis/reasons
Results/Observations
What conditions would make your arm muscles
tire quickly.
Describe the changes you feel as you bend your
arm
B: Continual Muscle
Stimulation
average
C: Restricted Blood
Flow
How do you think the feeling in your arm and
hand will change as you progress through your
trials?
D: Weight Lifting
Which arm will fatigue first? ________________
Explain why.
average
Left arm:
Right arm:
E: Varying
temperature
Do you think your arm will be affected?
Conclusion:
1. Did you experience muscle fatigue? Under what conditions?
2. How did the restriction of blood flow affect how many times you flexed your hand in the 20 second time frame?
3. From the results of this lab, what can you conclude about the relationship between the cardiovascular system
and muscle fatigue?
4. Study the graph you prepared in the Analysis. How do your results compare with the class data? Would you
consider your own results average, above average, or below average? Explain using specific data.
Analysis: Using data from “Step B: Continual Muscle Stimulation”, prepare a bar graph using your data & your
partner’s data as a side by side analysis. (x-axis: trial number; y-axis: number of flexes)