detecting electrical activity

• Muscles contract in response to nervous impulses, which are electrical signals
• Electrical signals in muscles can be detected by electrodes placed on the skin, connected to a computer to monitor the signals
• The procedure to monitor electrical signals in muscles is called electromyography (EMG)
• • Lifting a weight increases the amplitude of the trace on the graph, indicating more motor units are required
  • Muscle fatigue occurs when the muscle can no longer contract as forcefully
  • Fatigue is shown on the electromyogram by an increase in the amplitude of the trace, as the brain tries to activate more motor units to generate force
• To carry out the procedure:

  • Attach two electrodes to the muscle you want to record from (e.g., biceps muscle in the arm)
  • Place a third electrode on an inactive point (e.g., bony wrist area) as a control
  • Switch off unnecessary electrical equipment to reduce interference
  • Connect electrodes to an amplifier and a computer to monitor signals
  • Keep the muscle relaxed to see a straight line on the electromyogram
  • Contract the muscle to see spikes in the graph as motor units activate