“…FD gives a quantitative indication of the chaotic behavior of a signal, and is also related to the degree of interference of the signal, which is inversely related to the 'smoothness' of the signal (Mesin, Cescon, Gazzoni, Merletti, & Rainoldi, 2009a). At least eight different methods for estimating FD of sEMG waveforms have been applied in literature, including the box-counting method (Barnsley & Hurd, 1989), the Hurst exponent (Hurst, 1951), a method based on power spectral density (Kaplan, 1999;Raghav & Mishra, 2008;Spasic, 2007), the methods proposed by (Higuchi, 1988), (Sevcik, 2010), (Petrosian, 1995) and (Katz, 1988) and two variants of the latter (Castiglioni, 2010). These methods were compared and reviewed by (Coelho & Lima, 2014), who evidenced that the normalized version of the Katz's estimation method, followed by the Hurst exponent, significantly outperform the others in terms of generating more discriminatory features.…”