Chapter 2

Question 1

Motor unit recruitment measured

Answer 1

• Fire-wire electrodes are inserted into the muscle to record the activities of the muscle fibers in the electrodes immediate vicinity. Recognized by its waveform
• Spike-triggered averging: EMG impulses of single motor units used to trigger a signal avg that sums the whole-muscle force following the spike. This has been the primary method (identifying twitch speed and strength)
• Examining the spectral properties of the myoelectric signals from surface EMG electrodes
• Biochemical indexes of recruitment, measured through muscle fiber biopsies following exercise. Very difficult method to determine recruitment.

Question 2

Lengthening Contractions

Answer 2

Used everyday. Muscles lengthen when the force applied exceeds the force produced by the muscle. resulting in braking and storage of elastic energy. Motor units are recruited differently during short vs long contractions.

• motor unit pool is less activated
• Cortex uses diff strategy of motor unit recruitment
• Recruitment is preserved

Question 3

Coactivation

Answer 3

The simultaneous contraction of antagonist and agonist which serve to:
-Stabalize the joint
-Distribute pressure across the joint
-Decrease strain on ligaments and increase damping
Coactivation may add a metabolic cost and limit the expression of toque among the joint.

Question 4

Bilateral Deficit Phenomenon

Answer 4

This is when there is a slight weight loss in the maximal voluntary force of a muscle when the contaclateral muscle or muscle group contracts at the same time. This phenomena is not present in all subjects, some show no difference or bilateral facial

Question 5

Order of muscle fiber recruitment when preforming rhythmic complex excecise

Answer 5

During rhythmic complex contractions (running and cycling) recruitment is consistent with the size principle. (trends with depletion of glycogen)
Type I->IIa->IIab->IIb
# of fibers involved increase with intensity.

Question 6

Excitatory Postsynaptic Potential (EPSP) Partioning

and what type of muscle fibers are affected.

Answer 6

EPSP the strength of connections to motoneurons from Ia afferents from the same neuromuscular compartment is 1.6-2.3 times stronger than that from other compartments in the same muscle.

(twice as strong in same compartment than from others)

Question 7

Slow ramp isometric contractions v.s maintained isometric contractions

Answer 7

Both use size principal.

Slow-ramp: avoid coming to max firing rates before highest threshold reach max recruitment in order to recruit more units (insufficient surplus action)

Maintained: firing rates decrease gradually during constant force output.

Question 8

Isometric contractions v.s movement contractions

Answer 8

these contractions recruit differently but to output same contraction.

Isometric-recruit via slow-ramp and is preserved.
Movement-initial high frequency discharge of units.

Question 9

Determining maximal voluntary contraction (MVC)

Answer 9

MVC can be determined using twitch interpolation: nerve is stimulated while preforming MVC.

The added electrical force against absolute force=Linear relationship, MVC is where lines meet.

Question 10

Impact of order of muscle fiber recruitment on glycogen stores.

Answer 10

I>IIa>IIab>IIb

-When I and IIa fibers are totally depleted of glycogen it then goes to IIab and IIb (late adaptation)