title: The application of Hilbert-Huang transform in the analysis of muscle fatigue during cyclic dynamic contractions.
abstract: Surface electromyography (sEMG) is a common technique used in the assessment of local muscle fatigue. As opposed to static contraction situations, sEMG recordings during dynamic contractions are particularly characterised by non-stationary (and non-linear) features. Standard signal processing methods using Fourier and wavelet based procedures demonstrate well known restrictions on time-frequency resolution and the ability to process non-stationary and/or non-linear time-series, thus aggravating the spectral parameters estimation. The Hilbert-Huang transform (HHT), comprising of the empirical mode decomposition (EMD) and Hilbert spectral analysis (HSA), provides a new approach to overcome these issues. The time-dependent median frequency estimate is used as muscle fatigue indicator, and linear regression parameters are derived as fatigue quantifiers. The HHT method is utilised for the analysis of the sEMG signals recorded over quadriceps muscles during cyclic dynamic contractions. The results are compared with those obtained by the Fourier and wavelet based methods. It is shown that HHT procedure provides the most consistent and reliable assessment of spectral and derived linear regression parameters, given the time epoch width and sampling interval in the time domain. The suggested procedure successfully deals with non-stationary and non-linear properties of biomedical signals.
authors.affiliation: Faculty of Electrical Engineering and Computing, University of Zagreb, Unska 3, HR-10000 Zagreb, Croatia. vedran.srhoj-egekher@fer.hr
authors.forename: Vedran
authors.initials: V
authors.lastname: Srhoj-Egekher
authors.forename: Mario
authors.initials: M
authors.lastname: Cifrek
authors.forename: Vladimir
authors.initials: V
authors.lastname: Medved
mesh_terms: D000328:Adult; D004576:Electromyography / Q000379:methods; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D052097:Quadriceps Muscle; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult