Psychobiology of Fatigue

Question 1

Peripheral fatigue

Answer 1

reduction in maximal voluntary contraction force occuring during exercise; due to limitations in muscle itself

Question 2

Central fatigue

Answer 2

reduction in maximal voluntary contraction force occurring during exercise; NOT accompanied by a fall in maximal evocable force

Question 3

Voluntary force production

Answer 3

human volitional factor; you want to do it

Question 4

Evocable force production

Answer 4

amount of force the muscle or nerve can actually generate

Question 5

Twitch interpolation: dependent variables

Answer 5

• contraction intensity

- twitch-induced force

Question 6

Twitch interpolation: takeaways

Answer 6

• electrical stimulation of peripheral nerves
• additional force produced with stimulation even during short duration, fatigue-inducing exercise
• less twitch-induced force with more voluntary contraction
• more twitch-induced force with less voluntary contraction

Question 7

TMS stimulation: dependent variables

Answer 7

• MEP (motor evoked potential - measures motor-evoked electrical activity of muscle)
• torque (force produced / power output of muscle)
• silent period (cortical-spinal neuron inhibition following contraction)

Question 8

TMS: takeaways

Answer 8

with transcranial magnetic stimulation to brain during fatigue portion of elbow flexion:

• torque increases
• MEP size increases (elec. activity of muscle)
• silent period increases (longer inhibition of cortical-spinal neurons)

Question 9

mechanisms for central fatigue

Answer 9

1: reduction in descending output from motor cortex (changes in cortical-spinal neurons)
2: reduction in efficiency of output from motor cortex (motor neurons are less responsive to inputs from cortex)

Question 10

central fatigue in CFS patients

Answer 10

1: 4-min sustained voluntary contraction = greater and more increase in %MVC than control
2: endurance of isometric exercise = CFS patients had lower endurance times
3: TMS stimulation during biceps contraction = CFS patients have an increased TMS-induced twitch force

Question 11

ICSS - Burgess et al.

Answer 11

intracranial self-stimulation in rats
purpose: examine effects of reward center stimulation on fatigue in long-duration exercise
impact: reward region in brain (Ventral Tagmental Area) is likely involved in motivation for human physical activity
how? - stimulated reward center if rats kept running; VTA stimulated rats had significantly longer running times