Anterior Tibial Muscle Function Assessment Using Acoustic Myography and Electromyography

Ebrahimi-Takamjani, Ismail (1995) Anterior Tibial Muscle Function Assessment Using Acoustic Myography and Electromyography. PhD thesis, University of Glasgow.

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This thesis describes a series of experiments comparing the electrical and acoustic signals recorded from the human tibialis anterior muscle. Electromyography (EMG) is a widely used method of monitoring muscle activity. In many muscles its amplitude increases linearly with force and changes in the EMG/force ratio or shifts of the median frequency provide evidence of fatigue. However, in some circumstances it is difficult or impossible to record the EMG satisfactorily e.g. if there is sweat on the skin or in strong electrical fields or during electrical stimulation. Acoustic myography (AMG) is a more recent development. It is a non- invasive technique which may also be used as an indicator of skeletal muscle activity. Transverse oscillations of the muscle surface are detected with microphones or accelerometers. Their performance is not affected by sweating or electrical stimulation artefacts. The AMG is a much simpler signal than EMG and because it has a very narrow bandwidth it is easy to filter out noise. Like EMG, it has been found that the AMG increases with force but it is also known that, contrary to the EMG, the amplitude of AMG declines with force during fatiguing activity. The experiments described here investigate the relationships between the EMG, AMG amplitude and force in normal muscles and during muscle fatigue. In addition, the characteristics of the frequency spectra of EMG and AMG were investigated. The effect of muscle length on EMG and AMG characteristics were also studied. The contribution of blood flow to the AMG was studied by comparing the signals recorded with and without blood flow in the lower limb. A linear relationship was found between rectified integrated EMG (IEMG) and force in fresh and fatigued muscle. The slope of the relationship increased with fatigue. A similar relationship was found between the IAMG and force in the range 0-75% of maximum voluntary contraction in control conditions. However, the slope of the relationship between IAMG and force declined after fatiguing exercise. The EMG spectra from the tibialis anterior contained frequencies between 0 and 400 Hz. The median frequency increased linearly as the force of muscle contraction increased. The EMG median frequency decreased during sustained contractions as fatigue developed. However, the AMG contained a range of frequencies between 0 and 45 Hz. The median frequencies of the AMG also increased linearly with increasing force. However, the AMG frequency content was not significantly changed if fatigue developed at low forces such as 40% of maximum voluntary contraction but the median frequency declined significantly when the muscle was fatigued at forces above 60% of maximum. Changes in the length of tibialis anterior affected the force development, EMG and AMG characteristics. At shorter muscle lengths, the maximal voluntary force is reduced compared to the intermediate and longer lengths and the slope of the relationships between force and IEMG and IAMG increases. There were no significant differences in force or the relationships between force and IAMG and force and IEMG between the intermediate and longer lengths. There were no significant changes in the median frequencies of EMG and AMG at different muscle lengths. There were no significant changes in the characteristics of AMG and EMG when the blood flow to the lower limb was stopped by inflating an pressure cuff. It can be concluded that the contribution of blood flow to the AMG and EMG was insignificant. In conclusion, the AMG represents a mechanical counterpart of the electrical activity in muscle fibres. The IAMG and the AMG median frequency may be used to provide indirect information about force. Analysis of changes in the IAMG/force ratio or AMG median frequency might be used to identify the development of fatigue during contractions above 60% of maximum voluntary force.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: R H Baxendale
Keywords: Bioengineering, Biomechanics
Date of Award: 1995
Depositing User: Enlighten Team
Unique ID: glathesis:1995-74923
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Sep 2019 15:10
Last Modified: 27 Sep 2019 15:10

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