PEX-02-05.pdf

Name: courtney.sims Exercise 2: Skeletal Muscle Physiology: Activity 5: Fatigue in Isolated Skeletal Muscle Lab Report Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1. When skeletal muscle twitches fuse so that the peaks and valleys of each twitch become indistinguishable from each other, the muscle is in a state known as You correctly answered: d. complete (fused) tetanus. 2. When the stimulus frequency reaches a value beyond which no further increase of skeletal muscle force can occur, the muscle has reached its You correctly answered: c. maximal tetanic tension. 3. A decline in a muscle's ability to maintain a constant level of force, or tension, after prolonged, repetitive stimulation is called You correctly answered: c. fatigue. 4. Which of the following is not thought to be a contributing factor to the development of fatigue? You correctly answered: a. buildup of Ca2+ in the muscle fibers

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Experiment Results Predict Question: Predict Question: If the stimulator is briefly turned off for defined periods of time, what will happen to the length of time that the muscle is able to sustain maximal developed tension when the stimulator is turned on again? Your answer : b. The length of the rest period will proportionately increase the length of time for sustained muscle tension. Stop & Think Questions: Why does the stimulated muscle force begin to decrease over time despite the maintained stimuli? (Note that a decrease in maximal force indicates muscle fatigue is developing.) You correctly answered: d. More than one of these answers could be correct. Why did the length of the intervening rest period affect the length of time the skeletal muscle can maintain maximum tension once the stimulator is turned on again? You correctly answered: c. Intracellular concentrations of ADP and Pi declined during the rest period. Experiment Data: Voltage

Stimuli/sec

Rest Period (sec)

Active Force (g)

8.5 8.5 8.5 8.5

120 120 120 120

0 0 12 22

5.86 5.86 5.86 5.86

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Sustained Maximal Force (sec) 10 10 1.80 5.80

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Post-lab Quiz Results You have not completed the Post-lab Quiz.

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Review Sheet Results 1. When a skeletal muscle fatigues, what happens to the contractile force over time? Your answer: When the muscle gets very weak, the one thing that you see with the contractile force over time would be that it decreases as the muscle is not strong. 2. What are some proposed causes of skeletal muscle fatigue? Your answer: It would be buildup of lactic acid and calcium levels are low as that are the causes of muscle fatigue. 3. Turning the stimulator off allows a small measure of muscle recovery. Thus, the muscle will produce more force for a longer time period if the stimulator is briefly turned off than if the stimuli were allowed to continue without interruption. Explain why this might occur. How well did the results compare with your prediction? Your answer: My answer that I guessed was wrong as when doing the experiment I noticed that the stimulator was turned off, it was just resting as it decrease the amounts of calcium and lactic acid. 4. List a few ways that humans could delay the onset of fatigue when they are vigorously using their skeletal muscles. Your answer: A few ways would be to rest those sore muscles, do light exercises, or eat healthy with light exercise.

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