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EMG Dimitrov Spectral Fatigue Index (FInsm5)

Source: R/emg-fatigue.R
emgDimitrovIndex.Rd

Computes spectral moments \(M(k) = \int f^k\,PSD(f)\,df\) for \(k = -1, 0, \dots, 5\) over sliding windows and the Dimitrov fatigue index \(FInsm5 = M(-1)/M(5)\) per window. FInsm5 rises steeply with fatigue because spectral compression toward low frequencies simultaneously increases the low-frequency moment \(M(-1)\) and decreases the high-frequency moment \(M(5)\). The per-channel FInsm5-vs-time regression slope is attached as the "finsm5_slope" attribute.

Usage

emgDimitrovIndex(x, window_sec = 1, overlap = 0.5, assay_name = NULL)

Arguments

x

A PhysioExperiment object with EMG data.

window_sec

Analysis window in seconds (default: 1.0).

overlap

Overlap fraction between windows (default: 0.5).

assay_name

Input assay name (default: first assay).

Value

A data.frame with one row per channel per window, containing columns channel, window, time_sec, the moments m_minus1, m0, m1, m2, m3, m4, m5, and finsm5. The per-channel FInsm5 regression slope (index per minute) is available via attr(result, "finsm5_slope").

References

Dimitrov, G.V. et al. (2006). "Muscle fatigue during dynamic contractions assessed by new spectral indices." Medicine & Science in Sports & Exercise, 38(11), 1971-1979. doi:10.1249/01.mss.0000233794.31659.6d

See also

emgFatigueSlope() for MDF/MNF regression slopes, emgSpectralMoments() for the M0/M1/M2 moments, emgFatigue() for median/mean frequency tracking

Examples

sr <- 1000; n <- 6000
sig <- sin(2 * pi * 80 * seq_len(n) / sr) + rnorm(n, sd = 0.1)
pe <- PhysioExperiment(assays = list(raw = matrix(sig, ncol = 1)),
                       samplingRate = sr)
di <- emgDimitrovIndex(pe, window_sec = 1)
head(di)
#>   channel window time_sec m_minus1       m0       m1      m2        m3
#> 1       1      1      0.0 3.175804 254.6519 21325.03 2056167 299493123
#> 2       1      2      0.5 3.159098 252.3385 21070.24 2009293 283962046
#> 3       1      3      1.0 3.193799 254.9841 21316.86 2055038 301903375
#> 4       1      4      1.5 3.197576 256.2773 21477.77 2085573 311515124
#> 5       1      5      2.0 3.151104 252.5249 21052.55 1993245 277620319
#> 6       1      6      2.5 3.133642 250.1177 20883.55 1989383 281089669
#>            m4           m5       finsm5
#> 1 78405813142 2.894247e+13 1.097282e-13
#> 2 71952596330 2.614338e+13 1.208374e-13
#> 3 80725383077 3.051720e+13 1.046557e-13
#> 4 84513358334 3.210148e+13 9.960836e-14
#> 5 69773757053 2.544662e+13 1.238319e-13
#> 6 71707359747 2.639359e+13 1.187274e-13
attr(di, "finsm5_slope")
#>   channel slope_per_min r_squared    p_value
#> 1       1  1.611849e-13 0.2895953 0.08769738