PEX-02-07

Exercise 2: Skeletal Muscle Physiology: Activity 7: Isotonic Contractions and the Load-Velocity Relationship Lab Report Pre-lab Quiz Results You scored 20% by answering 1 out of 5 questions correctly. 1. During an isotonic concentric contraction, the Your answer : a. force generated by the muscle is less than the weight of the attached load. Correct answer: b. force generated by the muscle is greater than the weight of the attached load. 2. During an isotonic concentric contraction Your answer : a. the latent period decreases with heavier loads. Correct answer: b. the latent period increases with heavier loads. 3. During the latent period for an isotonic concentric contraction Your answer : b. the sliding filament mechanism causes the muscle to shorten. Correct answer: c. cross bridges cycle and, when muscle tension exceeds the load, muscle shortening occurs. 4. Muscle shortening velocity Your answer : d. is constant regardless of the load. Correct answer: 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.

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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? Your answer : b. isotonic ecentric Correct answer: c. isometric Experiment Data: Voltage

Length

Weight

8.5 8.5 8.5 8.5

75 75 75 75

0.5 1.0 1.5 2.0

Velocity (mm/msec) 0.100 0.057 0.022 0.000

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Twitch Duration (msec) 78.00 49.00 30.00 0.00

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Distance Lifted (mm) 4.0 2.0 0.5 0.0

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Post-lab Quiz Results You scored 33% by answering 2 out of 6 questions correctly. 1. Which of the weights allowed the fastest muscle shortening velocity? Your answer: d. 2.0-g weight Correct answer: a. 0.5-g weight 2. Which of the weights induced the longest latent period of the muscle contraction? Your answer: a. 0.5-g weight Correct answer: 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 Your answer: c. the muscle tension increases, but the muscle cannot lift the load. Correct answer: a. the length of the muscle changes. 6. When lifting a heavy load Your answer: a. the latent period is shorter than for lighter loads. Correct answer: d. the muscle shortening velocity is decreased in comparison with lighter loads.

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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 your arm extends downwards to the point of it being straight. (but not while it is straight) & when the arm rises from the down position back to the raised position.

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 occurs when there is a rise in muscle tension but no movement or contraction of the muscle. Cross bridges cycle and when the muscle tension exceeds the load, muscle shortening happens. The latent period increases as the weight of the load gets heavier, this is for the necessary force to be generated by the muscle 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: The shortening velocity refers to the speed of the contraction from the muscle shortening while lifting a load. 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. 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. I was wrong. I said that the shortening distance was going to increase. 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: The velocity of the shortening distance decreases with a heavier load so the repetitions will take longer. 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 muscle will still generate force and change length. This is an isotonic contraction.

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