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6.2 Applied Work Physiology: Localized Muscle Fatigue
When muscles get tired, intensity (magnitude) (biceps brachii EMG power) goes up
Frequency goes down
Peak of curves on original graph will move up and left basically
Local Muscle Fatigue
Local Muscle Physiology
Technology/Tesign: Suits that amplify muscle strength
One Nerve Fiber
and all muscle fibers innervated by that particular fiber
One nerve fiber can control multiple muscle fibers
Spinal nerve, spinal cord, cell body of neuron, nerve fiber, muscle fibers, myofibrils, sacromeres
How long can muscle work without getting tired? What is going on?
Asymptote: If less than 15% then you can basically do the activity forever.
WHY does this drop so quickly?
Contracting muscles squeeze blood vessels and don't allow blood to flow
The mechanical action of static muscle contraction restricts
through the muscle and forces anaerobic metabolism.
There is an increase, then a decrease in blood flow as grip contraction increases.
EMG - Electromyography
Measure electrical activity
EMG Electromyogram - "Electricity" "muscle" "graph"
Two ways: quantitative and qualitative
Both forms are indirect
Ask the workers!
Figure out where the workers are having issues
Subjective "discomfort" survey
Reducing Local Muscle Fatigue
Interjecting adequate rest between exertions
Reduce sustained/static loads
Evaluate static work postures to reduce the load moments on the various joints
Use of Floor Mats
Soft and thick floor mats seem to reduce leg swelling and discomfort
Symptoms of Muscle Fatigue
Local hot/jabbing pain
Reduced motion control
EMG decreases frequency increases amplitude
Increased strain injuries
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