Skeletal Muscle Fatigue

Question 1

Skeletal Muscle Fatigue

Answer 1

a) The inability to maintain the required power output which is related to a decline in either force or velocity
b) A condition in which there is a loss in the capacity for developing force or velocity of muscle resulting from muscle activity under a demand/load which is reversible by rest
c) The inability to maintain the required power output which is related to a decline in force, velocity and power which is reversible

Question 2

Sites of Fatigue

Answer 2

Central and Peripheral

Question 3

Components of Central

Answer 3

1) Planning of voluntary movement (includes motivation)
2) Motor cortex and the supraspinal outpouts (includes cooardinated afferemt amd efferent signals)
3) Upper motor neurons
4) Lower motor neurons

Question 4

Components of Peripheral

Answer 4

5) Neuromusclar Junction
6) Sarcolemma and T-Tubule
7) Sarcoplasmic Reticulum
8) Metabolic systems
9) Actin-Myosin Interaction

Question 5

Central Fatigue

Answer 5

Centeral Governor Model (CGM):
A regulatory mechanism in the brain selects an optimal ‘pace’ that will preserve homeostasis by continuosly adjusting intensity during exercise

Question 6

Peripheral Fatigue Sites: Impact on Neuromuscular Junction (NMJ)

Answer 6

No biochemical evidence that NMJ blockage is a primary cause of fatigue during exercise

Question 7

Peripheral Fatigue Sites: Impact on Sarcolemma and T- Tubule System

Answer 7

The quality of the Action Potentials (electrical signals) are changed

Question 8

Membrane Potential

Answer 8

Resting membrane potential is due to alot of sodium inside and outside

Question 9

Peripheral Fatigue Sites: Sarcolemma and T- Tubule System #1

Answer 9

1. Fatigue at the sarcolemma site is associated with a change in membrane potential:
   - Sodium (Na+) and Potassium (K+) imbalancL Na+/K+ ATPase becomes inhibited, membrane may become ‘leaky’ to ions
   - Exercise increase blood potassium levels
2. ) Sodium potassium pump itself starts shutting down
3. ) The membrane itself becomes leaky
4. ) Increase of blood potassium

Question 10

Peripheral Fatigue Sites: Sarcolemma and T- Tubule System #2

Answer 10

2. Fatigue at T-Tubule site is associated with a drop in the strength or size (amplitude) of the action potential:
   - Na+; K+ ion imbalance continues
   - Electrical signal not sufficient to activate ion channels in T-Tubules system to release calcium

Question 11

Peripheral Fatigue Sites: Impact on Sarcoplasmic Reticulum (Ca2+ movements) #3

Answer 11

3. A rediuction in the amount of Ca2+ being released from the sarcoplasmic reticulum, due to:
   - Depressed Ca2+ release from the SR
   - The calcium remaining in SR is more difficult to release- increased Ca2+ staying in SR
   - Decrease Ca2+ return to SR- relaxation becomes a concern
   - Generally referred to as Calcium Overload

Question 12

Peripheral Fatigue Site: Actin-Myosin Interaction-Contractile Force Generation

Answer 12

I. Increasing inorganic phosphate (Pi) in cytoplasmic space
IV. Build up of ADP slows down the A-M ATPase activity- crossbridge cycling rate
II. Increasing hydrogen ions levels will decrease the pH
III. With lower pH a decreased sensitivity of troponin (on actin filament) to calcium

Question 13

Peripheral Fatigue Site: Metabolic Pathways

Answer 13

A. Phosphagen Sources
i) Reduced levels or lower supply of creatine phophate (P) or phosphicreatine (PCr)
B. Anaerobic Glycolysis
i) Lower supply- reduced glycogen concentrations
ii) Build up or accumulation of intracellular components - H+
iii) POSSIBLY lactate itself
C. Aerobic- Oxidative Phosphorylation
i) Depleted glycogen will lower pyruvate supply and reduce ATP production
ii) Possible role of reactive oxygen species, but limited evidence