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Slides from my guest lecture in neurophysiology in the department of integrative physiology on muscle fatigue. Undergraduates were the intended audience.
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Muscle FatigueMike Pascoe, M.S.
“Check the Map”• How muscle activation is achieved by the
CNS
• AGING - long term change in the ability to produce force
• MUSCLE FATIGUE - short term change in the ability to produce force
Definition• “an exercise-induced reduction in the
capacity of muscle to produce force”
• IS NOT: Perceived weakness, tiredness
• IS: Activity related impairment of physiological processes that reduce the force generating capacity of muscle
• What does this look like?
Adaptations - Fatigue• Early observations 1884
• Fatigue begins soon after the onset of physical activity
Quantification• Reduction that occurs in the peak force during a
maximal voluntary contraction (MVC)
Forc
e (%
MV
C)
100
Before After
ExerciseFatigue
0
Sites of Fatigue• Not only contractile protein impairment, but also decrease
in activation signal from the brain
Recent Strategies• Cannot answer “what causes muscle fatigue?”
• Instead, ask “what causes task failure?”
• Our lab’s approach has been to focus on the mechanisms that cause task failure
• Mechanisms responsible for failure depend on the details of the task
• Involves comparing two performances and identifying the adjustments that limit the rate of the more difficult condition
Force Task Position Task
Maintain a submax force Maintain elbow angle
Task Failure
0
300
600
900
1,200
1,500
Force Task Position Task
Tim
e To
Fai
lure
(s)
Neural AdjustmentsFo
rce
Task
Posi
tion
Task
Clicker Question• Why is the time to task failure shorter for the
position task?
A. Motor units were recruited more rapidly
B. The target torque was lower in the force task
C. The elbow angle changed more during the force task
D. It was harder to maintain MVC during the position task
E. Because Mike said so
Clicker Question• Why is the time to task failure shorter for the
position task?
A. Motor units were recruited more rapidly
B. The target torque was lower in the force task
C. The elbow angle changed more during the force task
D. It was harder to maintain MVC during the position task
E. Because Mike said so
Neural AdjustmentsFo
rce
Task
Posi
tion
Task
Applications• Ergonomics
• Rehabilitation
• Training specificity
AppliedBasic
