Isotonic Contractions and the Load-Velocity Relationship

PhysioEx Lab Report Exercise 2: Skeletal Muscle Physiology Activity 7: Isotonic Contractions and the Load-Velocity Relationship Name: Date: 15 September 2020 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: force generated by the muscle is greater than the weight of the attached load. 2 During an isotonic concentric contraction You correctly answered: the latent period increases with heavier loads. 3 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. 4 Muscle shortening velocity You correctly answered: decreases with heavier loads. 5 An isotonic contraction of a muscle is one in which You correctly answered: the length of the muscle changes. Experiment Results Predict Question 1 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. Stop & Think Question 1 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. Experiment Data Voltage (v) Length (mm) Weight (g) Velocity* (mm/ms) Distance Time Time Twitch Lifted (contracting) (relaxing) Duration (mm) (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 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. 1 Which of the weights allowed the fastest muscle shortening velocity? You correctly answered: 0.5-g weight. 2 Which of the weights induced the longest latent period of the muscle contraction? You correctly answered: 1.5-g weight. 3 Which weight did the muscle contraction move the greatest distance? You correctly answered: 0.5-g weight. 4 Which of the weights allowed the longest duration of muscle contraction? You correctly answered: 0.5-g weight. 5 An isotonic contraction of a muscle is one in which You correctly answered: the length of the muscle changes. 6 When lifting a heavy load You correctly answered: 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 you lift your arm up from the straightened downward position, and then also when you return your arm to that downward state. 2 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 results of my prediction and this experiment were different. I predicted that the latent period would decrease, but the latent period increases due to the fact that it took more time to generate new force. 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: My prediction was wrong with this answer, as the latent period increases, the distance increases, and shortening velocity takes longer(increases) to lift the heavier object, and the contraction thus takes longer(increases). 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: My predictions were correct, the shortening velocity decreases with heavier equipment. 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: With an increase of weight comes an increase of time the latent period, whilst the shortening velocity speed decreases. 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: An isometric contraction. The muscle will generate force as the muscle stretches. The weight of the heavy equipment would pull the muscle length down, but this change in muscle length is not from the contraction, but from the weight itself.