Iworx Chapter 3 Experiment 1 Questions

Lab 3: Electromyography

Exercise 1

Dominant Forearm Circumference (mm): 290 |

Relative Grip Strength | Absolute Area of EMG activity | Absolute Area Under Force Curve |

Lowest | 0.146 | 20.722 |

Higher 1 | 0.277 | 39.464 |

Higher 2 | 0.465 | 67.197 |

Highest | 0.771 | 110.379 |

1.

2. There is a very linear positive relationship between the absolute area under the EMG signals and the absolute area under the force of the muscle contractions.

3. The muscle fibers do have a refractory period much like nerve cells do, as the motor neurons pass a signal through a synapse to the fibers, which then must pass a threshold before creating an action potential that propagates up and down the length of the fiber, much as we see in axons. As this action potential is the initial cause of a contraction, there is a period where the resting membrane potential must be restored before another contraction can take place, which creates absolute and relative refractory periods.

4. The amplitude of the EMG signal and the force of contraction increase due to a combination of factors occurring simultaneously. As more force is desired, the strength of the signal sent from the CNS will increase, but initially the strength will only be enough to activate small motor units. This means that only a small amount of the overall muscle fibers in the muscle, those that the small motor units are associated with, will be initially activated. As the signal increases, larger and larger motor units will get recruited in to the contraction, resulting in more muscle fibers contracting. Additionally, the stronger CNS signal creates a higher amplitude of action potentials travelling to and through the motor neurons, and in turn the muscle fibers. This increased amplitude can lead to the muscle fibers being activated faster than they can relax, as the refractory period for the action potential is much shorter than the time it takes a fiber to relax. This leads to prolonged contraction,...