[PhysioEX Chapter 2 exercise 6] PEX-02-06

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Exercise 2: Skeletal Muscle Physiology: Activity 6: The Skeletal Muscle Length-Tension Relationship Lab Report
Pre-lab Quiz Results
You scored 100% by answering 5 out of 5 questions correctly.

1. During an isometric contraction
   You correctly answered: d. 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: a. passive force.
3. Active force
   You correctly answered: b. 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: c. tetanic force
5. Passive force in skeletal muscle is largely caused by
   You correctly answered: c. the protein titin.

Experiment Results
Predict Question:
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 : a. An increase in muscle length will increase total force.
Stop & Think Questions:
Note the dip in total force at a muscle length of 90 mm. Why does this occur?
You correctly answered: d. At this muscle length, active force has decreased in value and passive force has not yet
increased to a significant value.
Experiment Data:
Voltage Length Active Force Passive Force Total Force
8.5 75 1.82 0.00 1.82
8.5 70 1.75 0.00 1.75
8.5 65 1.55 0.00 1.55
8.5 60 1.21 0.00 1.21
8.5 55 0.73 0.00 0.73
8.5 50 0.11 0.00 0.11
8.5 80 1.75 0.02 1.77
8.5 90 1.21 0.25 1.46
8.5 100 0.11 1.75 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: d. the muscle is contracting isometrically.
2. Which protein is mostly responsible for the development of passive force in a muscle?
   You correctly answered: d. titin
3. In skeletal muscle, active force stimulated through a range of muscle lengths
   You correctly answered: b. will utilize ATP hydrolysis to drive the cross bridge cycle.
4. Which if the following is not depicted in a typical skeletal muscle isometric length-tension curve?
   You correctly answered: a. time
5. Maximal active tension will be produced in a skeletal muscle fiber when
   You correctly answered: a. 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:
   force is changed by the starting resting length of the muscle.
   If muscle is lengthened past its resting length, the passive force is increased.
   If the muscle is shortened to its resting length, the active force increases.
2. What is the key variable in an isometric contraction of a skeletal muscle?
   Your answer:
   Muscle length because in isometric contraction, the muscle length does not change.
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:
   Active force depends on the rate of combine between actin and myosin.
   If the resting length of the muscle is shortened, there are more actin bound to myosin which increases the active force.
4. What skeletal muscle lengths generated passive force? (Provide a range.)
   Your answer:
   80-100 mm muscle lengths.
5. If you were curling a 7-kg dumbbell, when would your bicep muscles be contracting isometrically?
   Your answer:
   In situation when the bicep muscles fix its length.