Skeletal Muscle Physiology
Lab Summary Worksheet
Directions: Read the following directions before starting the lab.
Before starting each lab Activity, read the Overview and Introduction. This information will help you understand what you are doing in the lab. You do not have to pdf your lab – the only thing that you will submit for grading is this lab report. You will have to answer the Stop and Think Questions that are embedded in the lab instructions. You will not be graded on those questions; however, they will increase your understanding. Download this report, type your answers in Blue or highlight your answers after each question. Save the Lab Report again and upload it to the course.
Activity 1: The Muscle Twitch and the Latent Period
After reading the Overview and Introduction, Click on Experiment. Follow the directions on the left side of the lab to complete this activity. This first lab activity is intended to familiarize you with the elements of this lab. No assignments are connected to it, and there is no required data collection. If you do not conduct this activity, you may not understand Activities 5, 6 and 7.
Activity 5: Fatigue in Isolated Skeletal Muscle (10 points total)
After reading the Overview and Introduction, Click on Experiment. Follow the directions on the left side of the menu to complete the lab. Use the data chart to answer the following 2 questions. You do not have to submit your lab to be recorded.
Lab Analysis Questions (5 pts each)
1. Explain the effect that periods of recovery have on the force of a muscle, as compared to a continuous multiple stimulus fatigue. When a stimulus is provided, the muscle twitch is divided into latent, contraction, and relaxation. If continuous multiple stimuli are provided to a muscle without letting it to relax and recover its original shape, the muscle gets fatigued and cannot work properly
2. Does the number of recovery periods or the lengths of those recovery periods affect the force the muscle can exert? Explain your answer. When muscle is let to recover after stimulus provided then it’s not exposed to fatigue and can work more productively with larger force. Number of recovery periods or the lengths of those recovery periods affect the force the muscle can exert because muscle when gets relaxed, its momentum and doesn’t gets tired. And when the muscles are fully recovered, they can exert greater force then.
Activity 6: The Skeletal Muscle Length-Tension Relationship (15 points total)
After reading the Overview and Introduction, Click on Experiment. Follow the directions on the left side of the menu to complete the lab. Record your data in Chart 1 and use it to answer the following 2 questions. You do not have to submit your lab to be recorded. Do not Clear your Tracings before recording your data in Chart 1.
Chart 1: Isometric Contraction Results (5 pts)
Muscle length (mm)
Active Force (gms)
Passive Force (gms)
Total Force (gms)
Lab Analysis Questions (5 pts each)
1. Explain what is meant by active force and passive force. Active force is generated by the physiological contraction of the muscle. Passive force (due to protein titin) is generated by stretching the muscle and is due to the elastic properties of the tissue itself.
2. Explain why total force increases and decreases as the length of the muscle varies. Total force is the sum of passive and active forces. Active force and passive force change as small muscle will have a smaller contraction and stretch and, larger muscle will be having a larger contraction and stretch.
Activity 7: Isotonic Contractions and the Load-Velocity Relationship (25 points total) Notes:
After reading the Overview and Introduction, Click on Experiment. Follow the directions on the left side of the menu to complete the lab. Record your data in Chart 2 and use the chart to help answer the following 3 questions. You do not have to submit your lab to be recorded. Do not Clear your Tracings before recording your data in Chart 1.
Chart 2: Isotonic Contraction Results: Part 1 (4 pts)
Twitch Duration (msec)
Distance Lifted (mm)
Lab Analysis Questions (3 pts each)
1. What type of contraction occurred when the 2.0g weights was attached to the muscle? An isometric contraction of a muscle generates force without changing length.
2. Explain the relationship between resistance and the velocity of shortening. The relationship between the resistance and velocity of shortening is inverse. The velocity of shortening refers to the speed of the contraction from the muscle shortening while lifting a load. The greater the resistance, the shorter the velocity of shortening. The smaller the resistance, the larger the velocity of shortening.
3. Explain the relationship between resistance and distance lifted. The inverse relationship between resistance and distance lifted. The more resistance, less distance will be lifted by the muscle and when the resistance is less, distance lifted will increase.
Connections to Human Physiology (4 pts each)
Consider what you learned by conducted the lab activities and reading the Overview and Introductory information for each activity and answer the following questions.
4. If you tried to lift something very heavy, like your car, your muscles would contract and tire quickly. What type of muscle contraction occurs in this instance? Explain why your muscles would be unable to fully shorten, causing your attempts at lifting the car to fail. Lifting weights is the concentric action. When you try to lift a car, which is “isotonic contraction”. Isotonic contraction, tension remains unchanged and the muscle's length changes. Muscles get fatigued due to greater weight. As the weight of the load increases, initially velocity moves the weight decreases, which causes the muscles to tire. 5.
5. In an attempt to "bulk up" and increase the size of your muscles, you have begun a regular swimming regimen, in which you swim 30 minutes each day, four days each unit. After a month has passed, you notice that your stamina in the pool increases—you can swim much farther before your muscles begin to tire. However, your muscle size has not visibly increased. What type of exercises should you include in your daily regimen to build muscle size? Explain your answer. Biceps curls, triceps extensions, push-ups and pushdowns. The continuous contraction and stretch of the biceps and triceps leads to muscle size build up when this exercise is a part of daily routine. When muscle first contracts or stretches, the force it is able to produce is less than the force it is able to produce in subsequent movements within a relatively narrow time span.
6. If the fuel source for muscle contraction comes from the bloodstream, can you target specific areas of the body to “spot reduce” fat? For example, will lengthy sessions of repetitive abdominal crunches or sit-ups decrease the fat around the abdomen? No, you cannot control where your body reduces its fat. You have to reduce your overall body fat, and your then your abs will be able to show.