Workshop 1 EMG

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Workshop 1 EMG

• Brain Behaviour

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Electromyography

• Muscles consist of individual fibres, which
  contract when stimulated.
• Each fibre is stimulated by a single motor
  neuron. One motor neuron and the fibres it
  controls make up a single motor unit.
• Every time that neuron fires all the fibres in
  its motor unit contract.

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The neuromuscular junction

• Motor neurons release acetylcholine.
• This has an excitatory effect on muscle fibres.
• A single action potential in the motor nerve is
  enough to trigger an action potential in the
  muscle fibre.
• Depolarisation triggers the release of calcium
  ions, which trigger contraction.
• The potential (voltage) generated by one fibre is
  small (lt100mV).

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Muscle contraction tonus

• Muscle contraction is graded by varying
• The number of active motor units within the
  muscle.
• The frequency of firing of each motor unit.
• Skeletal muscles are normally slightly
  contracted, known as tonus. At any given time a
  small proportion of the motor units will be
  active.
• Exertion can increase the size of individual
  fibres and increase energy stores Hypertrophy.

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Applications of EMG

• Clinical applications
• Invasive recording used in assessment.
• Biofeedback
• Can aid rehabilitation after injury or stroke
• May have other applications e.g. forehead EMG
  biofeedback may reduce tension headache.
• EMG and covert behaviour e.g.
• subvocalisation while reading
• Facial EMG and emotion

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Facial Expressions and Emotion

• Feedback from our own expressions may influence
  emotional experience (Ekman, Levenson Friesen,
  1983).
• Emotional contagion may also occur. By
  mimicking others expressions and actions we may
  share their feelings (Lundqvist Dimberg, 1995).
• Dimberg et al. (2002) found that facial responses
  were elicited by emotional stimuli, even when
  subjects were instructed not to respond or to
  produce a differing expression.

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Recording

• By placing electrodes over the muscle we can
  record the signal generated by muscle
  contraction.
• Voltage is displayed continuously and recorded
  for analysis.
• The signal includes positive and negative waves
  and varies rapidly we also analyse integrated
  EMG (averages over 20 samples, ignoring the sign)

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Analysis

• We will obtain the EMG while participants perform
  four actions in a 2x2 design.
• Choose two from
• Heavy vs light weight
• Different movements (Raising, holding or
  lowering)
• Two individuals differing in gender or fitness
• Imagining a relevant or irrelevant movement.

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Imagining an action

• Imagining carrying out an action has often
  reported to increase activity in the muscle
  groups involved in the action e.g. Guillot et al.
  (2007) compared actual movements and imagining
  carrying out the same movements.
• Similar differences between muscles, and types of
  exercise were found in the lifting and mental
  imagery conditions.
• However, other studies suggest there may also be
  non-specific effects Concentration or effort may
  have general effects on muscle tension.

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Measurement

• The measurement boxes need to be set to display
• The minimum and maximum values and the range
• The mean integrated EMG
• We want these values for three repetitions in
  each condition.
• Values should be pasted into the Journal

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Writing Up

• You need to enter values and answer questions on
  the worksheet for each practical.
• You also need to copy
• the full data window, showing your recording
• the journal, with the values calculated during
  analysis pasted into it.
• Into the record sheet for the practical.