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.
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Activity 5: Fatigue in Isolated Skeletal Muscle
Note:
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
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 three phases i.e. latent, contraction, and relaxation. The latent period is a short period between the time of stimulation and the beginning of contraction. During contraction, the myofilaments are sliding past each other, and the muscle shortens and then the relaxation takes place when contraction has ended and the muscle returns to its normal resting state and length.
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. Fatigue is the buildup of lactic acid, ADP, and inorganic phosphate, and possibly oxygen debt. Whereas when the stimulus is applied with appropriate time intervals and let muscle recover itself, it can work more productively with greater force. Thus the best way to delay the onset of fatigue with intense exercise is to schedule brief periods of rest to allow muscle recovery.
Does the number of recovery periods or the lengths of those recovery periods affect the force the muscle can exert? Explain your answer.
As stated above, 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, regains its momentum and doesn’t gets tired. E.g. if we cut grass lower, we can mow our lawn less often. That is not some too-good-to-be-true gimmick. That is common sense. The more grass we cut off, the more time is needed to grow it back. Similarly, if we’re working more muscle fibers by exercising with more force, we can exercise less often. The more muscle fibers we exercise, the more time we need to recover. And when the muscles are fully recovered, they can exert greater force then.
Activity 6: The Skeletal Muscle Length-Tension Relationship
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 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
Muscle length (mm)
Active Force (gms)
Passive Force (gms)
Total Force (gms)
50
0.11
0.00
0.11
55
0.73
0.00
0.73
60
1.21
0.00
1.21
65
1.55
0.00
1.55
70
1.75
0.00
1.75
75
1.82
0.00
1.82
80
1.75
0.02
1.77
90
1.21
0.25
1.46
100
0.11
1.75
1.86
Lab Analysis Questions
Explain what is meant by active force and passive force.
Active force is generated by the physiological contraction of the muscle where as Passive force is generated by stretching the muscle and is due to the elastic properties of the tissue itself. This passive force is largely due to the protein titin, which acts as a molecular bungee cord.
Think of the muscle as having two force properties: it exerts passive force when it is stretched (like a rubber band exerts passive force) and active force when it contracts.
Explain why total force increases and decreases as the length of the muscle varies.
Total force is the sum of passive and active forces, and it is what we experimentally measure. According to the length of muscle, active force (generated by physiological contraction of muscle) and passive force (generated by stretching the muscle) change as small muscle will have a smaller contraction and stretch, similarly large muscle will be having a larger contraction and stretch so this leads to the variation in total force simultaneously.
Activity 7: Isotonic Contractions and the Load-Velocity Relationship
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
Voltage
Length
Weight
Velocity (mm/sec)
Twitch Duration (msec)
Distance Lifted (mm)
8.2
75
0.5g
1
78.00
4.0
8.2
75
1.0g
0.57
49.00
2.0
8.2
75
1.5g
0.22
30.00
0.5
8.2
75
2.0g
0.00
0.00
0.0
Lab Analysis Questions
What type of contraction occurred when the 2.0g weight was attached to the muscle?
In this case, the contraction is isometric. An isometric contraction of a muscle generates force without changing length. An example can be found when the muscles of the hand and forearm grip an object; the joints of the hand do not move, but muscles generate sufficient force to prevent the object from being dropped. Same is the case in question where 2.0g weight is attached to the muscle.
Explain the relationship between resistance and the velocity of shortening.
The velocity of shortening refers to the speed of the contraction from the muscle shortening while lifting a load. The relationship between the resistance and velocity of shortening is inverse. The greater the resistance, the shorter the velocity of shortening and the smaller the resistance, the larger the velocity of shortening.
Maximal shortening velocity is only attained with a minimal load. With a light load, the shortening velocity is at its Maximal shortening velocity. When the weight is heavy, the speed in which the muscle lifts the weight decreases in speed at a slower velocity.
Explain the relationship between resistance and distance lifted.
Same as above, there is an inverse relationship between resistance and distance lifted. If there is more resistance, less distance will be lifted by the muscle and when the resistance is less, distance lifted will increase.
Connections to Human Physiology
Directions:
Consider what you learned by conducted the lab activities and reading the Overview and Introductory information for each activity and answer the following questions.
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. While trying to lift a car, the contraction that takes place is “isotonic contraction”. In an isotonic contraction, tension remains unchanged and the muscle’s length changes.
Secondly, the act of lifting weights does result in temporarily shortened muscles. In this case, muscles would be unable to fully shorten, causing attempts at lifting the car to fail because car weight is greater and human power is much lesser comparatively. The muscles get fatigued due to greater weight. Moreover as the weight of the load increases, the initial velocity to move the weight decreases which cause the muscles to tire.
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.
When a 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. A myogram, a recording of a muscle twitch, reveals this phenomenon as the “treppe” or “staircase effect”. Treppe is thought to be caused by increased efficiency of the enzyme systems within the cell and increased availability of intracellular calcium. That’s the reason I can swim much farther before my muscles begin to tire.
Arm muscle is made up of fore arm, biceps and triceps and then connects to our shoulders. For muscle build up, I’ll have to concentrate on exercises that focus on two muscles i.e. biceps and triceps. Biceps curls, triceps extensions, push-ups and push-downs are some of the types. Push-ups are self-explanatory whereas push downs are the exact opposite movement. For push-ups, lower your body slowly to the floor until your upper arms is parallel to the floor. Hold this for a few seconds, and then push yourself up until your arms are extended again. 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.
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?
This idea has been dubbed the “Spot Reduction” myth. Unfortunately, this does not happen at all. In fact, it may be one of the least effective ways to actually reach your goal of less body fat or more-toned muscles. You cannot control where your body reduces its fat stores, so your goal should be to reduce total body fat stores.
However, what does happen is the underlying muscles, in this case the abdominals, get stronger, and sometimes larger. So if you still have belly fat and your abdominal muscles get larger, you may be just be pushing your fat further forward! What you need to do is reduce your overall body fat so you can show off the strong abs you’ve worked hard for.
