PhysioEx Exercise 2 Activity 7

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10/27/22, 4:37 PM PhysioEx Exercise 2 Activity 7 https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex2/act7/ 1/5 PhysioEx Lab Report Exercise 2: Skeletal Muscle Physiology Activity 7: Isotonic Contractions and the Load-Velocity Relationship Name: Selvana Labib Date: 27 October 2022 Session ID: session-f1762388-69e4-8bb9-a24d-ec1b772d6351 Pre-lab Quiz Results You scored 100% by answering 5 out of 5 questions correctly. Experiment Results Predict Question Stop & Think Question During an isotonic concentric contraction, the You correctly answered: force generated by the muscle is greater than the weight of the attached load. 1 During an isotonic concentric contraction You correctly answered: the latent period increases with heavier loads. 2 During the latent period for an isotonic concentric contraction You correctly answered: cross bridges cycle and, when muscle tension exceeds the load, muscle shortening occurs. 3 Muscle shortening velocity You correctly answered: decreases with heavier loads. 4 An isotonic contraction of a muscle is one in which You correctly answered: the length of the muscle changes. 5 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: The latent period will decrease, the shortening velocity will decrease, the distance will increase, and the contraction duration will increase. 1

10/27/22, 4:37 PM PhysioEx Exercise 2 Activity 7 https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex2/act7/ 2/5 Experiment Data Voltage (v) Length (mm) Weight (g) Velocity* (mm/ms) Distance Lifted (mm) Time (contracting) Time (relaxing) Twitch Duration (total) 8.5 75 0.5 0.100 4.0 40.00 38.00 78.00 8.5 75 1.0 0.057 2.0 35.00 14.00 49.00 8.5 75 1.5 0.022 0.5 23.00 7.00 30.00 8.5 75 2.0 0.000 0.0 0.00 0.00 0.00 *Distance divided by time (contracting). weight = 0.5 g duration of twitch = 78.00 msec velocity = 0.100 mm/msec distance lifted = 4.0 mm weight = 1.0 g duration of twitch = 49.00 msec velocity = 0.057 mm/msec distance lifted = 2.0 mm weight = 1.5 g duration of twitch = 30.00 msec velocity = 0.022 mm/msec distance lifted = 0.5 mm 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: isometric. 1

10/27/22, 4:37 PM PhysioEx Exercise 2 Activity 7 https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex2/act7/ 3/5 weight = 2.0 g duration of twitch = 0.00 msec velocity = 0.000 mm/msec distance lifted = 0.0 mm Post-lab Quiz Results You scored 100% by answering 6 out of 6 questions correctly. Which of the weights allowed the fastest muscle shortening velocity? You correctly answered: 0.5-g weight. 1 Which of the weights induced the longest latent period of the muscle contraction? 2

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10/27/22, 4:37 PM PhysioEx Exercise 2 Activity 7 https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex2/act7/ 4/5 Review Sheet Results You correctly answered: 1.5-g weight. Which weight did the muscle contraction move the greatest distance? You correctly answered: 0.5-g weight. 3 Which of the weights allowed the longest duration of muscle contraction? You correctly answered: 0.5-g weight. 4 An isotonic contraction of a muscle is one in which You correctly answered: the length of the muscle changes. 5 When lifting a heavy load You correctly answered: the muscle shortening velocity is decreased in comparison with lighter loads. 6 If you were using your bicep muscles to curl a 7-kg dumbbell, when would your muscles be contracting isotonically? Your answer: When using your bicep muscles to curl a 7-kg dumbbell, your muscles will be contracting isotonically when lifting the dumbbell towards the shoulder. 1 Explain why the delay between muscle stimulation and load movement 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 of the decrease of muscle twitch duration and velocity. In other words, the muscle length doesn't shorten as much with the heavier loads. 2 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: When the weight is heavy, the speed in which the muscle lifts the weight decreases in speed at a slower velocity. 3 Describe how the shortening distance changed as the load became heavier in this experiment. How well did the results compare with your prediction? 4

10/27/22, 4:37 PM PhysioEx Exercise 2 Activity 7 https://media.pearsoncmg.com/bc/bc_0media_ap/physioex/10/ex2/act7/ 5/5 Your answer: Shortening distance changed as the load became heavier because with an increase in weight, the shortening distance became shorter. 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: It takes longer to perform 10 reps lifting 10-kg than 5-kg, because with 5-kg, maximal shortening velocity is attained much faster. The heavier, the load, the slower the muscle twitch and the lighter the load, the faster the muscle twitch. 5 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: What's being described is an isometric contraction. The muscle would generate passive force when given an electrical stimulus but with the weight pulling down on the muscle, the muscle would not visibly move. Since the weight is puling down on the muscle, the muscle is going to lengthen but not because of a contraction, but because of the weight just pulling down on it. 6