Graph Analysis
  • 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
Motor Unit
  • 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

Rohmert Curve
How long can muscle work without getting tired? What is going on?
Rohmert Curve


  • 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 blood flow 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"
Measuring LMF
Two ways: quantitative and qualitative
Both forms are indirect
Ask the workers!
  • Figure out where the workers are having issues
  • Subjective "discomfort" survey
  • Psychophysical
Reducing Local Muscle Fatigue
Couple ways.
Adequate Rest
  • Interjecting adequate rest between exertions
  • most common
Reduce Loads
  • 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
  • Increased tremor
  • EMG decreases frequency increases amplitude
  • Increased strain injuries
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