LABORATORY REPORT: Recruitment and Isotonic and Isometric Contractions


Activity: Recruitment and Isotonic and Isometric Contractions
Name: kimberly mackey
Instructor: trisha tidd
Date: 06.26.2021
Predictions

  1. When the arm goes from resting to flexing, the amplitude and frequency of sEMG spikes will
    increase
  2. During flexion, the amplitude and frequency of sEMG spikes will _ during extension.
    be greater than
  3. Recruitment of motor units will be greatest when the load is
    5 pounds
    Materials and Methods
    Comparison of motor unit activation during muscle tone and concentric and eccentric isotonic contractions
  4. Dependent Variable
    amplitude and frequency of sEMG spikes
  5. Independent Variable
    muscle movement
  6. Controlled Variables
    total number of motor units present in muscle, muscle load, subject’s physical condition
    Recruitment during isometric contractions
  7. Dependent Variable
    amplitude and frequency of sEMG spikes
  8. Independent Variable
    muscle load
  9. Controlled Variables
    total number of motor units present in muscle, muscle movement, subject’s physical condition
  10. What does the acronym sEMG stand for?
    Surface electromyograpgy
  11. During a muscle contraction, what is recorded on a sEMG?
    Amplitude (mV) and frequency of sEMG spikes (motor unit action potentials).
  12. Spike numbers were measured during a ____msec period.
    200
    Results
    Table 3. Muscle Tone (Resting) and Isotonic Contractions
    Amplitude (mV) Frequency of Spikes (number per 0.2 msec sampling period)
    Rest Concentric Eccentric Rest Concentric Eccentric
    Subject 1 0.10 0.41 0.35 1 20 20
    Laboratory Report/ kimberly mackey/ Recruitment and Isotonic and Isometric Contractions/ trisha tidd/ 06.26.2021/ Page [1] of [4]
    Laboratory Report
    Amplitude (mV) Frequency of Spikes (number per 0.2 msec sampling period)
    Rest Concentric Eccentric Rest Concentric Eccentric
    Subject 2 0.11 0.48 0.39 1 21 20
    Subject 3 0.12 0.41 0.36 1 20 20
    average 0.11 0.43 0.37 1 20 20
    Graph 1. sEMG Amplitudes and Frequencies at Rest and During Isotonic Contractions
    Amplitude (mV)
    0
    0.1
    0.2
    0.3
    0.4
    0.5
    1 2 3
  13. Rest
  14. Concentric
  15. Eccentric
    Frequency (spikes number per 0.2 sec time period)
    0
    5
    10
    15
    20
    25
    1 2 3
  16. Rest
  17. Concentric
  18. Eccentric
  19. When the biceps brachii was at rest, were motor units activated as indicated by amplitude and frequency of sEMG spikes?
    Yes, but at a very low rate (0.12 mV) because normal resting muscles exhibit muscle tone due to the stimulation of a small number of motor
    units. This asynchronous activation keeps all the motor units
  20. What was the change, if any, of motor unit stimulation (reflected in amplitude and frequency of sEMG spikes) during concentric
    contraction against a 5 pound load?
    Yes, there was a change – from 0.12 mV at rest to 0.43 mV during a concentric contraction against a 5 pound load. The increase of amplitude
    was of 0.31 mV. As for the frequency of sEMG spikes, there w
  21. Did motor unit stimulation, (reflected in amplitude and number of spikes per 0.2 sec time period) increase, decrease, or not change
    when biceps brachii went from concentric to eccentric contraction with a 5 pound load?
    Motor unit decreased in regards to the amplitude: it went from 0.43 mV in a concentric contraction to 0.32 mV in an eccentric contraction with a
    5 pound load. As for the frequency of sEMG spikes it di
  22. Did the arm flex or extend during the eccentric contraction of the biceps brachii?
    The arm extends during the eccentric contraction.
    Table 4. Isometric Contractions
    Isometric Contraction (Amplitudes (mV))
    Rest 0 lb 2 lb 5 lb 10 lb 20 lb
    Subject 1 0.10 0.081 0.156 0.230 0.470 1.240
    Subject 2 0.11 0.092 0.164 0.220 0.460 1.290
    Subject 3 0.12 0.085 0.170 0.250 0.480 1.200
    average 0.11 0.086 0.163 0.233 0.470 1.240
    Frequency of Spikes (number per 0.2 msec sampling period)
    Rest 0 lb 2 lb 5 lb 10 lb 20 lb
    Subject 1 1 16 18 21 20 21
    Subject 2 1 16 17 21 20 20
    Laboratory Report/ kimberly mackey/ Recruitment and Isotonic and Isometric Contractions/ trisha tidd/ 06.26.2021/ Page [2] of [4]
    Laboratory Report
    Frequency of Spikes (number per 0.2 msec sampling period)
    Rest 0 lb 2 lb 5 lb 10 lb 20 lb
    Subject 3 1 15 17 21 20 20
    average 1 16 17 21 20 20
    Graph 2. sEMG Amplitudes and Frequencies at Rest and During Isometric Contractions Under
    Different Loads
    Amplitude (mV)
    0
    0.3
    0.6
    0.9
    1.2
    1.5
    1 2 3 4 5 6
  23. Rest
  24. 0 lb
  25. 2 lb
  26. 5 lb
  27. 10 lb
  28. 20 lb
    Frequency (spikes number per 0.2 sec time period)
    0
    5
    10
    15
    20
    25
    1 2 3 4 5 6
  29. Rest
  30. 0 lb
  31. 2 lb
  32. 5 lb
  33. 10 lb
  34. 20 lb
  35. Describe how amplitude of sEMG spikes changed with increasing muscle load.
    From rest to the isometric contraction with 0 lbs. a slight decrease in amplitude can be observed (from 0.12 mV to 0.087 mV). But, by increasing
    the load during the isometric contractions, the amplit
  36. Describe how frequency of sEMG spikes changed with increasing muscle load.
    As the load started increasing so did the frequency of sEMG until it reached an optimal point of 21 per 0.2 msec at the 10 lb threshold.
  37. Based on changes in amplitude and frequency of sEMG, did motor unit activation increase, decrease, or stay the same with
    increasing muscle load?
    The motor unit activation increased with increasing muscle load because activated motor units are contracting with greater frequency.
  38. Do you think that the force of isometric contraction increased, decreased, or stayed the same as muscle load increased?
    The force of the isometric contraction increased as the muscle load increased.
  39. Which would be a better predictor of increase in force of contraction, change in sEMG amplitude of spikes or change in sEMG
    frequency of spikes?
    Change in sEMG frequency of spikes.
    Discussion
  40. Discuss the importance of muscle tone.
    Muscle tone is very important because it allows the body to maintain its posture (e.g. keeping the head upright and preventing it from falling
    forward). Tone means tension, i.e. the skeletal muscles undergo a small amount of tension due to involuntary contractions of the motor units.
    Although the skeletal muscles are kept firm by the muscle tone, this is not strong enough to produce movement. Another area, where muscle
    tone plays an important role, is in smooth muscle tissue (e.g. gastrointestin
  41. Discuss the importance of motor unit stimulation during eccentric isotonic contraction.
    Laboratory Report/ kimberly mackey/ Recruitment and Isotonic and Isometric Contractions/ trisha tidd/ 06.26.2021/ Page [3] of [4]
    Laboratory Report
    The importance of motor unit stimulation during eccentric isotonic contraction is to try and keep the motor unit stable when muscle tension
    resists an action. During an eccentric contraction, the tension exerted by the myosin cross-bridges resists movement of a load and slows the
    lengthening process.
  42. Discuss how increasing the number of motor units stimulated affects force.
    Different motor units in a muscle are recruited in a specific order, depending on the physical activity that needs to be performed. If a task that
    needs to be performed requires only weak contractions in order to fulfill it, then only slow oxidative fibers are activated. If more force is needed,
    then fast oxidative–glycolytic fibers are also stimulated. In order to reach maximum force the help of fast glycolytic fibers is enlisted together with
    SO and FOG fibers. Maximum force occurs when all mo
  43. Discuss how increasing frequency of motor unit stimulation affects force.
    The muscle tension developed by a contracting muscle is determined by the frequency of stimulation of motor units and the number of motor
    units stimulated. If the contracting motor units are stimulated again before the relaxation phase of a muscle twitch is complete, then the next
    contraction will produce a greater force. Increasing the frequency of muscle stimulation produces sustained force generation. Muscle tension
    depends on the frequency of stimuli.
  44. During arm flexion, what type of contraction would the triceps brachii be exhibiting: concentric isotonic contraction, eccentric
    isotonic contraction, isometric contraction.
    eccentric isotonic contraction.
  45. During arm extension, what type of contraction would the triceps brachii be exhibiting: concentric isotonic contraction, eccentric
    isotonic contraction, isometric contraction.
    concentric isotonic contraction.
  46. As muscle load is increased, which muscle fiber type is recruited first, second, and last?
    The first muscle fiber type recruited is the slow oxidative; the second one recruited is the fast oxidative-glycolytic and the last one is the fast
    glycolytic fibers.
  47. Describe the importance of this order. Include affect on force of contraction and fatigue.
    Recruitment is the process of increasing the number of active motor units to increase force developed by a muscle. An increase in the number
    of motor units involved in contraction increases the contraction force of the muscle. Usually, recruitment involves activation of different motor
    units to help delay fatigue. The weaker, more fatigue resistant motor units (slow oxidative motor units) are recruited first, with stronger motor
    units (less fatigue resistant) added if more force is needed in re
  48. Restate your predictions that were correct and give data from your experiment that support them. Restate your predictions that
    were not correct and correct them, giving with supporting data from your experiment that supports your corrections.
    My predictions were correct. When the arm goes from resting to flexing, the amplitude and frequency of sEMG spikes will: increase. It went from
    0.12 to 0.43 mV and from 1 to 19 per 0.2 msec. Also, my second prediction was confirmed: during flexion, the amplitude and frequency of sEMG
    spikes will be greater than during extension. It went from 0.43 to 0.32 mV, but the frequency of spikes stayed the same (19 per 0.2 msec).
    Application
  49. Flaccid muscles do not exhibit muscle tone. Explain how muscles become flaccid.
    Muscles become flaccid as a result of damaging the motor neurons that serve the skeletal muscle. If the motor neurons are damaged or cut,
    then a state of limpness occurs and the muscle loses its tone.
  50. In the experiment “Muscle Tone and Concentric and Eccentric Isotonic Contractionsa”, the muscle contracts isometrically prior to
    the concentric isotonic contraction.
    In isometric muscle contraction the muscle maintains the same length, but the tension in the muscle increases. It is similar to holding a weight in
    a static position for a prolonged period of time. Although the length of the muscle remains fixed, the muscle is developing tension. If movement
    occurs, then the muscle shortens and we get a concentric isotonic contraction (during arm flexion).
  51. Explain why the muscle contracts isometrically before it shortens. The nerve that innervates the biceps brachii muscle is the
    musculocutaneous nerve. Explain what effect damage to this muscle would have on contractile force and recruitment of motor units
    in the biceps brachii muscle.
    The biceps brachii is responsible for flexing the forearm at the elbow joint; supinate the forearm at radioulnar joints, and flexing the arm at
    shoulder joint. Damage to the musculocutaneous nerve will have repercussion on the biceps brachii muscle’s capability to perform different
    actions, leading to loss of muscle strength, poor muscle tone, and sensory loss, weak or absent biceps tendon reflex.
    Laboratory Report/ kimberly mackey/ Recruitment and Isotonic and Isometric Contractions/ trisha tidd/ 06.26.2021/ Page [4] of [4]
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