LABORATORY REPORT

Activity 3: Recruitment and Contractions

Name:

Instructor:

Date:

PREDICTIONS

1. When the arm goes from resting to flexing, the amplitude and frequency of sEMG spikes will:

2. During flexion, the amplitude and frequency of sEMG spikes will ______during extension.

3. Recruitment of motor units will be greatest when the load is:

MATERIALS AND METHODS

Comparison of motor unit activation during muscle tone and concentric and eccentric isotonic contractions

1. Dependent Variable

2. Independent Variable

3. Controlled Variables

Recruitment during isometric contractions

1. Dependent Variable

2. Independent Variable

3. Controlled Variables

4. What does the acronym sEMG stand for?

5. During a muscle contraction, what is recorded on a sEMG?

6. Spike numbers were measured during a ____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?

2. What was the change, if any, of motor unit stimulation (reflected in amplitude and frequencyof sEMG spikes)during concentric contraction against a 5 pound load?

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?

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

See Table 4: Isometric Contractions

See Graph 2: sEMG Amplitudes and Frequencies at Rest and During Isometric Contractions under Different Loads

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

6. Describe how frequency of sEMG spikes changed with increasing muscle 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?

8. Do you think that the force of isometric contraction increased, decreased, or stayed the same as 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?

DISCUSSION

1. Discuss the importance of muscle tone.

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

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

4. Discuss how increasing frequency of motor unit stimulation affects force.

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

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

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

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

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 experimentthat supports your corrections.

APPLICATION

1. Flaccid muscles do not exhibit muscle tone. Explain how muscles become flaccid.

2. In the experiment “Muscle Tone and Concentric and Eccentric Isotonic Contractions”, the muscle contractsisometrically prior to the concentric isotonic contraction.

3. 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.