Chapter 2 - Motor Unit Recruitment During Different Types of Movements Flashcards
How is motor unit recruitment measured? Identify the various methods used.
fire-wire electrodes: are inserted into the muscle in question to record the activities of the muscle fibers in the electrodes immediate vicinity.
The spike-triggered averaging technique has been used in conjunction with intramuscular motor unit recording to generate information about the order in which units are recruited during simple contractions.
Biochemical indexes (biopsies)
What is excitatory postsynaptic potential partitioning and what type of muscle fibers is affected?
Excitatory postsynaptic potential (EPSP) portioning is the strength of connections to motoneurons from the afferents from the same neuromuscular compartment is 1.6 to 2.3 times stronger than that from other compartments in the same muscle.
Compare and contrast slow ramp isometric contractions and maintained isometric contractions
Slow ramp isometric contraction units are recruited from smallest to largest twitch force and from slowest to fastest twitch contraction time. This system is used to avoid low threshold units via maximal firing rates before the highest threshold units are maximally recruited.
Maintained isometric contractions does not recruit additional motor units. Firing rates decrease gradually during constant force output.
How are isometric contractions different than contractions involving movement?
Motor units are recruited differently but generate some general contractions. Isometric contractions > order recruit seen slow-ramp is preserved. Movement contractions > initial high frequency discharge of units.
What are lengthening contractions?
Lengthening contractions is when the muscles lengthen when the force applied exceeds the force produced by the muscle; this results to breaking and storage of elastic energy. Motor units are recruited differently based on the length of contractions. Lengthening contractions happens in our everyday activities.
What is the purpose of coactivation?
Coactivation is the simultaneous contraction of antagonists and agonists and is a common phenomenon.
Coactivation serves to stabilize the joint, distribute pressure across the joint, decrease the strain on ligaments during forceful contractions, and increase damping (reduce friction)
What is bilateral deficit phenomenon?
When the contralateral muscle or muscle group contracts at the same time there is a slight weight loss in max voluntary force.
Not at in all subjects, some show no difference.
What is the order of muscle fiber recruitment when performing rhythmic complex exercise?
The order of muscle fiber recruitment use the same process as the size principal. This is determined by the results drawn from the glycogen rates that use the same principal.
Type I > IIa > IIab > IIb
fibers involved increase w/intensity
What impact does order of muscle fiber recruitment have on glycogen stores?
I > IIa > IIab > IIb
Glycogen depletion in this order. Once I & IIa are fully depleted then goes on to IIa & IIb
What are the methods used to determine maximal voluntary contractions?
Twitch interpolation
Nerve stimulation while performing MVC (maximal voluntary contraction)
Linear relationship is between the added electric force the absolute force. MVC are where those two meet.
