Powerphys Week 2 Lab Report: Activity 3 - Recruitment and Contractions

LABORATORY REPORT

Activity 3: Recruitment and Contractions
Name:
Instructor: Ruth Peterson
Date: 07/17/2014

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 _be greater_____ during extension.

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

1. Dependent Variable amplitude and frequency of sEMG spikes.
2. Independent Variable muscle movement.
3. Controlled Variables total number of motor units present in muscle, muscle load.

Recruitment during isometric contractions

1. Dependent Variable amplitude and frequency of sEMG spikes.
2. Independent Variable muscle load.
3. Controlled Variables total number of motor units present in muscle, muscle movement, subject's physical condition.

4. What does the acronym sEMG stand for?
Surface electromyograpgy

5. During a muscle contraction, what is recorded on a sEMG?
Amplitude and frequency
6. Spike numbers were measured during a __200__msec period.

RESULTS

See Table 3: Muscle Tone (Resting) and Isotonic Contractions
See Graph 1: sEMG Amplitudes and Frequencies at Rest and During Isotonic Contractions

1. 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 of 0.12 mV because normal resting muscles exhibit muscle tone because of the stimulation of a small number of motor units. This activation keeps all the motor units within a muscle in shape.

2. 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 with a 5 pound load. The increase of amplitude was 0.31 mV. For the frequency of sEMG spikes there was an increase from 1 at rest to 19 during concentric contraction with a 5 pound load. The change was 18 per 0.2 msec.

3. 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). The frequency of sEMG spikes did not change from concentric to eccentric contraction with a 5 pound load, it stayed the same (19 per 0.2 msec).

4. Did the arm flex or extend during the eccentric contraction of the biceps brachii?

The arm extends during the eccentric contraction.

5. Describe how amplitude of sEMG spikes changed with increasing muscle load.

A gradual increase can be seen in the amplitude of sEMG spikes with increasing muscle load. From rest to the isometric contraction with 0 lbs. a small decrease in amplitude can be observed (from 0.12 mV to 0.087 mV). By increasing the load during the isometric contractions the amplitude started increasing (ex: for 2 lbs the amplitude was 0.166 mV to 1.250 mV amplitude for a 20 lb weight).

6. 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 21 per 0.2 msec at the 10 lb load.

7. 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 more quickly.

8. 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.

9. 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

1. Discuss the importance of muscle tone.
Muscle tone is important because it allows us to maintain our body posture . It also plays a large role when it comes to smooth muscle tissue. Lastly, it helps maintain the blood pressure throughout the body.

2. Discuss the importance of motor unit stimulation during eccentric isotonic contraction?
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.

3. Discuss how increasing the number of motor units stimulated affects force.

Different motor units in a muscle are used in a certain order based on the physical activity that needs to be performed. If the thing that needs to be performed needs only weak contractions in order to preform it, then only slow oxidative fibers are activated. If more force is needed then fast oxidative–glycolytic fibers are also activated.

4. 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.
5. During arm flexion, what type of contraction would the triceps brachii be exhibiting: concentric isotonic contraction, eccentric isotonic contraction, isometric contraction.

eccentric isotonic contraction

6. During arm extension, what type of contraction would the triceps brachii be exhibiting: concentric isotonic contraction, eccentric isotonic contraction, isometric contraction

concentric isotonic contraction

7. As muscle load is increased, which muscle fiber type is recruited first, second, and last?

the first muscle fiber type recruited: the slow oxidative the second one recruited: the fast oxidative-glycolytic the last one: the fast glycolytic fibers

8. Describe the importance of this order. Include affect on force of contraction and fatigue.

An increase in the number of motor units involved in contraction increases the contraction force of the muscle. Normally recruitment involves activation of different motor units to help prevent fatigue. The slow oxidative motor units are recruited first, with stronger motor units, that are less fatigue resistant, added if more force is needed in response to a greater muscle load. Motor units having many muscle fibers are capable of more forceful contractions than the ones having only a couple fibers. Increasing the number of motor units contracting at the same time also increases the force. After long periods of muscle contraction muscle fatigue sets in. The muscle cannot maintain force of contraction. Fatigue is typically from changes in the muscle fiber.

9. 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. My second prediction was correct as well, during flexion the amplitude and frequency of sEMG spikes will be greater than during extension. It went from 0.43 to 0.32 mV. Lastly, recruitment of motor units was greatest at 5 pounds.

APPLICATION

1.Flaccid muscles do not exhibit muscle tone. Explain how muscles become flaccid. Muscles become flaccid if the motor neurons that serve the skeletal muscle are damaged.

2. In the experiment “Muscle Tone and Concentric and Eccentric Isotonic Contractions”, the muscle contracts isometrically prior to the concentric isotonic contraction.
The muscle is developing tension. If movement is made then the muscle shortens and it results in a concentric isotonic contraction.

3.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.
Damage to the musculocutaneous nerve will effect the biceps brachii muscle’s ability to perform different actions, and cause loss of muscle strength, poor muscle tone, and sensory loss, weak or absent biceps tendon reflex.