Iphy 4720 | Muscle Fatigue Guest Lecture

Muscle Fatigue Mike 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)

Force (%MVC)

100

Exercise

Fatigue

0

Before

After

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?”

•

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

Instead, ask “what causes task failure?” Our lab’s approach has been to focus on the mechanisms that cause task failure

Force Task

Position Task

Maintain a submax force

Maintain elbow angle

Task Failure Time To Failure (s)

1,500 1,200 900 600 300 0

Force Task

Position Task

Force Task

Position Task

Neural Adjustments

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

Force Task

Position Task

Neural Adjustments

Applications • Ergonomics • Rehabilitation • Training specificity Basic

Applied