[PhysioEX Chapter 2 exercise 5] PEX-02-05

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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

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) Sustained Maximal Force
(sec)
8.5 120 0 5.86 10
8.5 120 0 5.86 10
8.5 120 12 5.86 1.80
8.5 120 20 5.86 5.00

Post-lab Quiz Results
You scored 100% by answering 5 out of 5 questions correctly.

1. During cross bridge cycling in skeletal muscle, force is created by the
   You correctly answered: c. power stroke of the myosin heads.
2. The term tetanus refers to
   You correctly answered: b. sustained muscle tension due to repetitive stimuli.
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. During fatigue
   You correctly answered: c. the number of active cross bridges begins to decline although the rate of stimulus delivery
   (frequency) remains constant.
5. If an intervening rest period is imposed on active skeletal muscle
   You correctly answered: c. the development of fatigue will be delayed.

Review Sheet Results

1. When a skeletal muscle fatigues, what happens to the contractile force over time?
   Your answer:
   When a skeletal muscle fatigues, contractile force decrease because force isn't generated any more after reaching maximal
   tetanic tension by previous contractile activity.
2. What are some proposed causes of skeletal muscle fatigue?
   Your answer:
   Lactic acid, ADP, phosphate and low calcium in blood.
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:
   By turning the stimulator off, a period of rest is created, thus allowing the concentrations of intercellular concentrations of
   Lactic Acid, ADP, and Pi to decrease. With these concentrations being at a decreased level, the length of time that the
   muscle is able to maintain maximum tension increases.
4. List a few ways that humans could delay the onset of fatigue when they are vigorously using their skeletal muscles.
   Your answer:
   do multiple sets of low repeted exercise.
   take a few breaks.
   to make muscle durable, exercise frequently.