Fatigue
• Sensations
• = inability to maintain
a given workload, or
decrement in
performance
• Energy demand
exceeds ATP
production capability
• Cause is dependent on
intensity and duration
• Association or
causation
• Compartmentalization
• Environment
• Fiber type, training
status, type of activity
• Oxygen
ATP and fatigue
• Fatigue often
occurs without a
significant drop in
ATP levels
– Compartmentalization
– Protective effect
CP and fatigue
• CP drops in 2
phases
• Relative work
intensity affects
rate and extent of
depletion
Phosphocreatine and intensity
• After ~5 sec CP is ~80% depleted, and speed
decreases
• J. Hirvonen, European Journal of Applied Physiology, 1987. Vol 56; 253-259
• J. Hirvonen, Canadian Journal of Sport Sciences, 1992, Vol. 17:2; 141-144
Phosphate
• As phosphogens
deplete Pi ↑
– Inhibit PFK
– Displace Ca++ from
troponin
• f
Lactic acid
• Lactate anions vs.
H+ protons
• ↓pH
– Inhibit PFK
– Displace Ca++ from
troponin
– Pain receptors
– Free energy of ATP
– Inhibit FFA release
Calcium
• Ca++ uptake into mitochondria
– Increased O2 consumption for Ca++ removal
– Decreased Ca++ in SR
• Ryanodine receptor fatigue
– Lactate anion, H+
• Decreased responsiveness
Long distance aerobic exercise
• Glycogen depletion
associated with fatigue
• Prolonged
submaximal exercise
• > 60 minutes
Glycogen depletion and sensation
Selective glycogen depletion
• Intensity
determines FT
dependence and
glycogen usage
CHO during exercise
Central fatigue
• Central Nervous
System
– Motor unit recruitment
– Motor unit firing rate
• Evidence for and
against
• Neural stimulation
• Psyche (Arousal)
• Serotonin
Peripheral Neural factors
• Peripheral nervous system
• Neuromuscular junction
– neurotransmitters, synaptic
cleft, receptors
• Excitation-contraction
coupling; with repeated
stimulation there is a
possibility of blocking the
action potential through
the t-tubules, decreasing
Calcium release
Peripheral mechanical factors
• Cross bridge cycling
• disruption of actin &
myosin, sarcomere,
sarcolemma, SR
• Ca++ availability
• H+, Pi block troponin,
inhibit SR Ca++ release,
inhibit enzymes
• ATP availability; SR,
Myosin head