[PhysioEX Chapter 2 exercise 7] PEX-02-07

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Exercise 2: Skeletal Muscle Physiology: Activity 7: Isotonic Contractions and the Load-Velocity Relationship Lab Report
Pre-lab Quiz Results
You scored 100% by answering 5 out of 5 questions correctly.

1. During an isotonic concentric contraction, the
   You correctly answered: b. force generated by the muscle is greater than the weight of the attached load.
2. During an isotonic concentric contraction
   You correctly answered: b. the latent period increases with heavier loads.
3. During the latent period for an isotonic concentric contraction
   You correctly answered: c. cross bridges cycle and, when muscle tension exceeds the load, muscle shortening occurs.
4. Muscle shortening velocity
   You correctly answered: a. decreases with heavier loads.
5. An isotonic contraction of a muscle is one in which
   You correctly answered: a. the length of the muscle changes.

Experiment Results
Predict Question:
Predict Question: As the load on the muscle increases, what will happen to the latent period, the shortening velocity, the
distance that the weight moves, and the contraction duration?
Your answer : c. The latent period will decrease, the shortening velocity will decrease, the distance will increase, and the
contraction duration will increase.
Stop & Think Questions:
What kind of contraction did you observe when you attached the 2.0 gram weight to the skeletal muscle and stimulated a
contraction?
You correctly answered: c. isometric
Experiment Data:
Voltage Length Weight Velocity
(mm/msec)
Twitch Duration
(msec)
Distance Lifted
(mm)
8.5 75 0.5 0.100 78.00 4.0
8.5 75 1.0 0.057 49.00 2.0
8.5 75 1.5 0.022 30.00 0.5
8.5 75 2.0 0.000 0.00 0.0

Post-lab Quiz Results
You scored 100% by answering 6 out of 6 questions correctly.

1. Which of the weights allowed the fastest muscle shortening velocity?
   You correctly answered: a. 0.5-g weight
2. Which of the weights induced the longest latent period of the muscle contraction?
   You correctly answered: c. 1.5-g weight
3. Which weight did the muscle contraction move the greatest distance?
   You correctly answered: a. 0.5-g weight
4. Which of the weights allowed the longest duration of muscle contraction?
   You correctly answered: a. 0.5-g weight
5. An isotonic contraction of a muscle is one in which
   You correctly answered: a. the length of the muscle changes.
6. When lifting a heavy load
   You correctly answered: d. the muscle shortening velocity is decreased in comparison with lighter loads.

Review Sheet Results

1. If you were using your bicep muscles to curl a 7-kg dumbbell, when would your muscles be contracting isotonically?
   Your answer:
   When the arm rises from the down position back to the raised position and when your arm extends downwards to the point
   of it being straight
2. Explain why the latent period became longer as the load became heavier in the experiment. How well did the results
   compare with your prediction?
   Your answer:
   The latent period became longer because it takes more time to generate the force required. It counteracts with my
   prediction.
3. Explain why the shortening velocity became slower as the load became heavier in this experiment. How well did the
   results compare with your prediction?
   Your answer:
   Maximal shortening velocity is only attained with a minimal load.
   With a light load, the shortening velocity is at its Maximal shortening velocity.
   When the weight is heavy, the speed in which the muscle lifts the weight decreases in speed at a slower velocity.
   Thus shortening velocity bacame slower as I predicted.
4. Describe how the shortening distance changed as the load became heavier in this experiment. How well did the results
   compare with your prediction?
   Your answer:
   The shortening distance decreased with the heavier load.
   This result counteracts with my prediction.
5. Explain why it would take you longer to perform 10 repetitions lifting a 10-kg weight than it would to perform the same
   number of repetitions with a 5-kg weight.
   Your answer:
   Because as the weight of the load increases, the latent period time increases and the shortening velocity speed decreases.
   With the lighter weight, the muscle is contracted quicker in both latent and shorteningvelocity speeds
6. Describe what would happen in the following experiment: A 2.5-g weight is attached to the end of the isolated whole
   skeletal muscle used in these experiments. Simultaneously, the muscle is maximally stimulated by 8.5 volts and the platform
   supporting the weight is removed. Will the muscle generate force? Will the muscle change length? What is the name for this
   type of contraction?
   Your answer:
   The force is generated from stretching the muscle caused by the recoil of the tissue.
   The muscle changing length would not be from the result of muscle contractions, but only from the weight pulling down.
   This type of contraction would be Isometric.