skeletal muscle and fatigue Flashcards
(12 cards)
3 types of motor units
Type 1 Slow contracting/slow fatiguing Oxidative
Type 2a Intermediate Mixed
Type 2b/x Fast contracting/fast fatiguing Glycolytic
aerobic pathway
Type 1 and 2a
Energy sources: intracellular stores of lipid and glucose plus some entry.
Use O2 in mitochondria
Very efficient!
1 glucose makes 38 ATP
1 FFA makes 100+ ATP
anaerobic pathway
Energy source: glucose via glycolytic pathway
Uses glucose inside the cell.
Very short term.
1 glucose makes 2ATP
plus 2 lactate molecules
Limited by muscle stores of creatine phosphate.
sources at max effort
ATP stores and Phosphocreatine deplete in few seconds
Anaerobic glycolysis can contribute for a few minutes; Type 2b fibres
Aerobic metabolism dominates after 3-5 minutes: Type 2a + Type 1 fibres
Type 2a and Type 1 fibres use a mix of glucose and lipids.
Long duration exercise is mostly fuelled by lipids
number of motor units in a muscle
small/large
Quadriceps - small number of large units Extraoccular- large number of small unit
types of motor units in a muscle
Soleus, slow, fatigue resistant, 80% Type 1 Gastroc, fast, quick fatigue, 80% Type 2b
Most muscles have a mix of type 1 and 2
low force contractions
Say below 25% of max force
Use Type 1 (slow fatiguing), efficient oxidative metabolism of glucose and lipids.
This needs oxygen. Muscle blood flow continues through low force contractions.
high force contractions
Say above 50% of max force
Uses all Types 1, 2a and 2b, fatigue develops quickly.
Circulation obstructed, low oxygen for 1 and 2as, inefficient glycolysis in the 2bs
peripheral fatigue
within muscles fibres
Failure of excitation-contraction coupling, T tubule action potential, SR activation, Ca++ release
Failure of force generation at cross bridges
Failure of ATP generation by depletion of energy stores
central fatigue
within the nervous system
Loss of excitability of motor cortex,
Reflex inputs from ‘metabo-receptors’ in muscle .
Can also include failure of transmission in peripheral nerve and neuromuscular junctions (probably pathological)
max exercise and ATP
Max exercise increases the demand for ATP x 1000
Fatigue is NOT due to reductions in [ATP]
Even at end of flat-out
If ATP runs out, muscle goes into rigor not fatigue
However, during fatigue [ADP], [Pi], [H+] all increase. These changes impair calcium fluxes and impair force delivery
central fatigue- sensory inputs
Central Actions of Group III and IV muscle afferents.
Ergoreceptors and
Mechanoreceptors and Nociceptors
