Electromyogram and Stretch Reflex Experiment-

Part 1- Grip Strengths and Electromyogram (EMG) Activity

Exercise 1: EMG Intensity and Force

Aim- To determine the relationship between the EMG intensity and force of contraction.

Questions-

1. In your plot of average muscle force as a function of the mean EMG integral (using the points 5 muscles clinches), is there a linear relationship between the mean EMG integral and the averaged muscle force?
2. Does the amplitude of the EMG signal and the force of contraction increase because a finite number of motor units are firing more often, or because more motor units are recruited to fire, or because of combination of these two?

Exercise 2: EMG Intensity and Fatigue in Dominant Arm

Aim- To observe the relationship between the length and strength of a muscle contraction and EMG activity in the dominant forearm.

Exercise 3: EMG Intensity and Force in the Non-Dominant Arm

Aim- To determine the relationship between the intensity of the EMG activity and the force of a muscle contraction in the subject's non-dominant forearm for comparison.

Questions-
1. Is one of the subject's forearms stronger than the other? Use the maximum grip strength from each arm to determine this answer? Calculate the percent difference in maximum grip strengths from each arm.
2. Does the stronger forearm have a higher ratio of maximum grip force to the mean EMG absolute integral than the weaker forearm? Use the slops of the force-EMG activity graphs for each forearm to determine this answer. Calculate the percent difference in the slop of the force-EMG activity graph from each arm.
3. Is there a difference between the circumference of the dominant and non-dominant forearms? Calculate the percent difference between the circumferences.
4. Is there a relationship between the circumference of the forearms and the maximum force developed? If there is, what is it?
5. If there is a difference in the circumference of the forearms is it caused by a difference in the number of muscle fibers in the forearm or the diameter of each muscle fiber in the forearm? Explain.

Exercise 4: EMG Intensity and Fatigue in Non-Dominant Arm

Aim- To observe the relationship between the length and strength of a muscle contraction and EMG activity in the non-dominant forearm.

Part II- Stretch Receptors and Reflexes

Exercise 1: EMG Recording and Reflex Timing

Aim- To determine conduction tyime from stimulus to response in the Achilles tendon reflex arc.

Questions

1. Which muscles are involved in plantar flexion and dorsiflexion of the ankle?
2. Is the Achilles reflex inhibited or enhanced by voluntary muscle activity in the gastrocnemius? Note that a contracting muscle resists stretch, so the stretch receptors will send fewer APs to the CNS.
3. Is the Achilles reflex facilitated during the Jendrassik's Maneuver (voluntary muscle activity an another part of the body)? Speculate on the mechanism of enhancement or inhibition. Since AP Conduction Velocity is roughly constant, could it be a change in the time that it takes either to initiate an AP at the muscle spindle in one case or the time for transmission in the Sp. Cord in the other?
4. Do isometric contractions in other muscle groups facilitate the Achilles reflex response? Speculate on the mechanism of enhancement or inhibition that these muscles employ.
5. Besides excitatory inputs from stretch receptors, what synaptic inputs might influence the activity of spinal motorneurons.

Exercise 2: Antagonistic Muscles in Achilles Stretch Reflex

Aim: To study muscles working in opposition to each other that flex and extend extremities.

Questions-

1. Compare the amplitudes (by eye) of the EMG integrals from the gastrocnemius during each of the four activities. When was gastrocnemius activity the greatest? The least?
2. Compare the amplitudes of the EMG integrals from the tibialis anterior during each of the four activities. When was tibialis anterior activity the greatest? The least?
3. How does EMG activity in the gastrocnemius correlate to EMG activity in the tibialis anterior?
4. Name some other locomotive activities that require coordination of antagonists.
5. What roles would stretch reflexes play in these locomotive activities?