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Normalize EMG Amplitude

Source: R/emg-amplitude.R
emgAmplitudeNormalize.Rd

Normalizes EMG amplitude data by a per-channel reference value. "mvc" divides by the per-channel maximum of a maximum-voluntary- contraction trial (percentage-of-MVC). "peak" divides by the within-trial peak so each channel ranges from 0 to 1. "rvc" divides by the per-channel mean amplitude of a sub-maximal reference voluntary contraction trial (percentage-of-RVC). "dynamic_peak" divides by a centered moving maximum, tracking a time-varying peak within the trial.

Usage

emgAmplitudeNormalize(
  x,
  method = c("mvc", "peak", "rvc", "dynamic_peak"),
  mvc_data = NULL,
  rvc_data = NULL,
  rvc_window = NULL,
  assay_name = NULL,
  output_assay = "normalized"
)

Arguments

x

A PhysioExperiment object (amplitude data).

method

Normalization method: "mvc" (maximum voluntary contraction), "peak" (within-trial peak), "rvc" (sub-maximal reference voluntary contraction), or "dynamic_peak" (centered moving maximum).

mvc_data

A PhysioExperiment containing MVC trial data (required for "mvc"). Must have the same number of channels as x.

rvc_data

A PhysioExperiment containing the sub-maximal reference-task data (required for "rvc"). Must have the same number of channels as x.

rvc_window

Optional window. For "rvc", a length-2 numeric c(start, end) in seconds selecting the portion of rvc_data over which the mean reference amplitude is computed (default: the whole reference trial). For "dynamic_peak", the moving-maximum window length in seconds (default: 0.5).

assay_name

Assay to normalize (default: first assay).

output_assay

Output assay name (default: "normalized").

Value

A PhysioExperiment object with an additional assay named output_assay containing normalized amplitude values. For "peak" and "dynamic_peak", values are scaled to a peak. For "mvc"/"rvc", values are proportions of the reference (multiply by 100 for percentage-of-MVC / percentage-of-RVC).

Details

Input is assumed to be amplitude data (a rectified signal or an emgEnvelope() output). MVC and RVC normalization are scale-invariant to a gain applied to both the signal and its reference trial.

References

De Luca, C.J. (1997). "The use of surface electromyography in biomechanics." Journal of Applied Biomechanics, 13(2), 135-163. doi:10.1123/jab.13.2.135

Yang, J.F. & Winter, D.A. (1984). "Electromyographic amplitude normalization methods: improving their sensitivity as diagnostic tools in gait analysis." Archives of Physical Medicine and Rehabilitation, 65(9), 517-521.

Burden, A. & Bartlett, R. (1999). "Normalisation of EMG amplitude: an evaluation and comparison of old and new methods." Medical Engineering & Physics, 21(4), 247-257. doi:10.1016/S1350-4533(99)00054-5

See also

emgEnvelope() for computing amplitude envelopes prior to normalization, emgAmplitudeFeatures() for windowed amplitude features, emgFatigue() for fatigue analysis, emgOnsetDetect() for muscle activation onset detection

Examples

set.seed(1)
amp <- matrix(abs(rnorm(1000 * 2, sd = 0.3)), nrow = 1000, ncol = 2)
pe <- PhysioExperiment(
  assays = list(raw = amp),
  colData = S4Vectors::DataFrame(label = c("EMG1", "EMG2"),
                                 type = c("EMG", "EMG")),
  samplingRate = 1000)
# percentage-of-RVC using a sub-maximal reference (here, the trial itself)
pe_rvc <- emgAmplitudeNormalize(pe, method = "rvc", rvc_data = pe)
colMeans(SummarizedExperiment::assay(pe_rvc, "normalized"))  # ~ 1
#> [1] 1 1