PhysioEx Lab Report Exercise 2: Skeletal Muscle Physiology Activity 6: The Skeletal Muscle Length-Tension Relationship Name: Date: 15 September 2020 Pre-lab Quiz Results You scored 100% by answering 5 out of 5 questions correctly. 1 During an isometric contraction You correctly answered: the skeletal muscle is generating force, but it remains at a ﬁxed length. 2 The force that results from muscles being stretched is You correctly answered: passive force. 3 Active force You correctly answered: is determined by the amount of myosin bound to actin. 4 When you generate the isometric length-tension curve, which of the following forces will not be indicated on your screen? You correctly answered: tetanic force. 5 Passive force in skeletal muscle is largely caused by You correctly answered: the protein titin. Experiment Results Predict Question 1 Predict Question: As the resting length of the muscle is changed, what will happen to the amount of total force the muscle generates during the stimulated twitch? Your answer: An increase in muscle length will increase total force. Stop & Think Question 1 Note the dip in total force at a muscle length of 90 mm as compared to the total force at a muscle length of 80 and 100 mm. Why does this occur? You correctly answered: At this muscle length, active force has decreased in value and passive force has not yet increased to a signiﬁcant value. Experiment Data Voltage (v) Length (mm) Active Force Passive Force Total Force 8.5 75 1.82 0 1.82 8.5 50 0.11 0 0.11 8.5 80 1.75 0.02 1.77 8.5 100 0.11 1.75 1.86 Muscle Length = 75 mm Active Force = 1.82 Passive Force = 0 Total Force = 1.82 Active Force Passive Force Total Force Muscle Length = 75 mm Active Force = 1.82 Passive Force = 0 Total Force = 1.82 Muscle Length = 50 mm Active Force = 0.11 Passive Force = 0 Total Force = 0.11 Active Force Passive Force Total Force Muscle Length = 50 mm Active Force = 0.11 Passive Force = 0 Total Force = 0.11 Muscle Length = 80 mm Active Force = 1.75 Passive Force = 0.02 Total Force = 1.77 Active Force Passive Force Total Force Muscle Length = 80 mm Active Force = 1.75 Passive Force = 0.02 Total Force = 1.77 Muscle Length = 100 mm Active Force = 0.11 Passive Force = 1.75 Total Force = 1.86 Active Force Passive Force Total Force Muscle Length = 100 mm Active Force = 0.11 Passive Force = 1.75 Total Force = 1.86 Post-lab Quiz Results You scored 100% by answering 5 out of 5 questions correctly. 1 When a skeletal muscle is stimulated and generates force but remains at a ﬁxed length You correctly answered: the muscle is contracting isometrically. 2 Which protein is mostly responsible for the development of passive force in a muscle? You correctly answered: titin. 3 In skeletal muscle, active force stimulated through a range of muscle lengths You correctly answered: will utilize ATP hydrolysis to drive the cross bridge cycle. 4 Which of the following is not depicted in a typical skeletal muscle isometric length-tension curve? You correctly answered: time. 5 Maximal active tension will be produced in a skeletal muscle ﬁber when You correctly answered: the ﬁber is at its resting length. Review Sheet Results 1 What happens to the amount of total force the muscle generates during the stimulated twitch? How well did the results compare with your prediction? Your answer: My prediction was correct, when there is an increase to muscle length, the total force increases. When there is a decrease to muscle length, there is a deceased in total force. 2 What is the key variable in an isometric contraction of a skeletal muscle? Your answer: The length-tension relationship. 3 Based on the unique arrangement of myosin and actin in skeletal muscle sarcomeres, explain why active force varies with changes in the muscle's resting length. Your answer: When the skeletal muscle's resting length increases, there is more time for myosin bridges to return to their starting position. 4 What skeletal muscle lengths generated passive force? (Provide a range.) Your answer: 80 mm - 100 mm. 5 If you were curling a 7-kg dumbbell, when would your bicep muscles be contracting isometrically? Your answer: As you lift the dumbbell up.