Table 3.

Fatigue indices in frequency domain.

Reference	Fatigue indices
Merletti and Lo Conte [76]	Mean frequency (MNF)
De Luca [77]	Median frequency (MDF)
Khanam and Ahmad [78]	Peak frequency (PKF)
Khanam and Ahmad [78]	Mean power (MNP)
Khanam and Ahmad [78]	Total power (TTP)
Altaf et al. [79]	The 1st, 2nd, and 3rd spectral moments (SM1, SM2, and SM3)
Phinyomark et al. [80]	Power spectrum ratio (PSR)
González-Izal et al. [81]	Instantaneous frequency variance (Fvar)
Georgakis et al. [75]	Averaged instantaneous frequency (AIF)
Dimitrov et al. [82]	Dimitrov's spectral fatigue index (FInsm5)