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How does muscle fatigue affect the amount of work that muscles can do?

Worksheet: 224-W10-Muscle-Fatigue-LabDownload

Background

As skeletal muscles contract and relax, they move bones in your body. This work requires energy. Muscles get energy from ATP molecules made during the process of cellular respiration. During continuous activity, the muscles begin to use up their energy supply and oxygen and start to accumulate waste products. As a result, the muscles become fatigued, losing their ability to contract. In this lab, you will observe how muscle fatigue affects the amount of work that muscles can do. Make a prediction about how exercise will affect the amount of work that muscles can do. Work in pairs or trios, but everyone should do each exercise. You and your partner(s) will take turns doing the following experiments.

Materials

  •  Stopwatch
  • Tennis Ball (or rolled up socks)

Arm Flexors and Extensors

1. Using your non-writing hand, stretch out your arm, keeping the palm of your hand upward. Raise your hand by bending your arm at the elbow. Then lower your hand by straightening at the elbow. Try to keep your upper arm steady as you move your hand up and down.

2. Continue raising and lowering your hand for 1 minute. Move it as rapidly as you can without straining yourself or losing control of the motion. Have your partner count and record the number of times you can raise and lower your hand in 1 minute.

3. Repeat step 2 seven more times. Do not stop between trials.

4. Get your data from your partner, and enter it into your own worksheet.

5. Switch roles with your partner and repeat the exercise.

DON’T STOP EXERCISING. REALLY PUSH IT. DO NOT STOP BETWEEN TRIALS.

1 min2 mins3 mins4 mins5 mins6 mins7 mins8 mins
          

In the worksheet, graph the number of repetitions you completed during each minute of the experiment. (Assign appropriate units to the Y-axis, based on the maximum number of reps you did in a minute).

  • After how many trials did your arm muscles become obviously fatigued?
  • How does the data show this?
  • Describe how your muscles felt. Which muscles experienced the most fatigue?

Foot Plantar Flexors and Dorsiflexors

1. Stand with your legs shoulder width apart. Perform a calf raise by raising your heels and standing up on your toes. Then relax your heels back to the ground.

2. Perform this exercise for 100 seconds without stopping. Throughout this period, your partner will record the number of calf raises you do every 10 seconds.

3. Get your data from your partner, and record it in your worksheet.

DON’T STOP EXERCISING. REALLY PUSH IT. DO NOT STOP BETWEEN TRIALS.

10 sec20 sec30 sec40 sec50 sec60 sec70 sec80 sec90 sec100 sec
            

In the worksheet, graph the number of repetitions you completed during each minute of the experiment. (Assign appropriate units to the Y-axis, based on the maximum number of reps you did in a minute).

  • As the exercise progressed, what happened to the number of repetitions in each 10 second interval?
  • By looking at your results of your calf raises, pinpoint when you first had a lot of lactic acid buildup.
  • How do you know?
  • Did you feel a burning sensation?
  • If so, how long did it take for that feeling to disappear?

Finger and Hand Flexors and Extensors

1. Grasp the tennis ball in your non-writing hand and squeeze enough to cause a dent in the ball with the heel of the hand.

2. You will perform this exercise without stopping for 100 seconds. Every 10 seconds, your partner will record the number of squeezes.

3. Get your data from your partner, and record it in your worksheet.

DON’T STOP SQUEEZING. REALLY SQUEEZE. DO NOT STOP BETWEEN TRIALS.

10 sec20 sec30 sec40 sec50 sec60 sec70 sec80 sec90 sec100 sec
            

Using the space below, graph the number of repetitions you completed during each minute of the experiment. (Assign appropriate units to the Y-axis, based on the maximum number of reps you did in a minute).

  • How did your squeezing hand and arm feel towards the end of the experiment?
  • What muscles experienced the most fatigue?
  • Does this correspond with the part of your body that seemed to be doing the work?

Follow-up Questions

  • Muscles work in opposing pairs. Were you able to able to feel this during each of the exercises? (If not, perform the movements a few times for each activity, and focus on which muscles can be felt moving). Explain why, in physiological terms, muscles must be paired in this way.
  • What was the cause of any burning sensation you felt during the activities?
  • Why did your ability to continue to perform the exercises decrease over time? (Explain in terms of ATP and glycogen)
  • What do you think the be the effect of resting for 10 minutes between trials. What would occur in the body?
  • With what you now know, what sort of cellular respiration do you think is involved in walking or running long distances?
  • What sort of cellular respiration do you think is involved with sprinting?

After you complete the muscle fatigue activities, complete the PhysioEx activities in Exercise 2: Skeletal Muscle Physiology:

Review Questions: PhysioEx-Ex2-Skeletal-Muscle-Worksheet-1Download