The influence of an increase in the level of force on the EMG power spectrum of elbow extensors

  • Martin Bilodeau
  • A. Bertrand Arsenault
  • Denis Gravel
  • Daniel Bourbonnais


It has been proposed that the mean power frequency (MPF) of the electromyogram (EMG) power spectrum increases gradually with force of contraction and that this increase is a function of the fiber-type content of the muscle investigated and the inter-electrode distance (IED) used when recording the EMG signals. In order to test these hypotheses, the values of the MPF of two elbow extensor muscles, triceps brachii (TB, 65% fast twitch fibers) and anconeus (AN, 65% slow twitch fibers), were compared at different levels of contraction. Subjects (n =13) produced ten static ramp elbow extensions [0–100% maximum voluntary contraction (MVC)]. EMG signals of each muscle were recorded with two pairs of surface miniature electrodes having IEDs of 6 mm and 30 mm respectively. MPFs were obtained at each of the following levels: 10, 20, 40, 60, 80 and 100% MVC. Statistical analyses indicated that the MPF of AN increased significantly (P<0.05) up to 60% MVC. In contrast, the MPF values for TB showed no significant change across different levels of contraction (P>0.05). Since skinfold was on average 3.2 times thicker over TB than over AN it is suggested that the low-pass filtering effect of the skin could have prevented the observation of an increase of the MPF for TB. It thus appears that changes of the MPF with the level of force, as disclosed by surface electrode recordings, is specific to each muscle. Consequently one has to account for factors such as thickness of the skinfold when it comes to the determination of the fiber-type content of different muscles within a subject.

Key words

Electromyography Power spectral analysis Fiber type Elbow extensor muscles 


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Copyright information

© Springer-Verlag 1990

Authors and Affiliations

  • Martin Bilodeau
    • 1
    • 2
  • A. Bertrand Arsenault
    • 1
    • 2
  • Denis Gravel
    • 1
    • 2
  • Daniel Bourbonnais
    • 1
    • 2
  1. 1.School of Rehabilitation, Faculty of MedicineUniversity of MontrealMontrealCanada
  2. 2.Research CentreMontreal Rehabilitation InstituteMontrealCanada

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