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EMG Co-Contraction Index

Source: R/emg-cocontraction.R
emgCoContraction.Rd

Quantifies simultaneous activation of an agonist-antagonist muscle pair from their amplitude envelopes, using one of three established indices. Input channels are treated as (non-negative) amplitude envelopes; with normalize = TRUE each is first scaled to its own peak so the two muscles are amplitude-comparable.

Usage

emgCoContraction(
  x,
  agonist,
  antagonist,
  method = c("falconer_winter", "rudolph", "frost"),
  normalize = TRUE,
  window_sec = NULL,
  assay_name = NULL
)

Arguments

x

A PhysioExperiment object of EMG amplitude envelopes.

agonist, antagonist

Channel index (integer) or channel label (character) of the two muscles. The indices are interchangeable for all three methods (the indices are symmetric in the pair).

method

Co-contraction index: "falconer_winter" (default), "rudolph", or "frost".

normalize

If TRUE (default), peak-normalize each channel to [0, 1] before computing the index.

window_sec

Optional non-overlapping window length in seconds for a time-resolved index. If NULL (default) only the whole-signal summary is returned.

assay_name

Input assay name (default: first assay).

Value

A list with:

method

The method used.

summary

The whole-signal co-contraction index (a scalar).

timeseries

If window_sec is given, a data.frame with columns window, time_sec and cci (one row per window); otherwise NULL.

Details

"falconer_winter"

Falconer & Winter (1985) percent co-contraction: \(2\sum\min(a,b) / \sum(a+b) \times 100\). 100 when the two envelopes are identical, 0 when they never overlap.

"rudolph"

Rudolph et al. (2000) co-contraction index: the mean over time of \((\ell/h)(\ell+h)\) with \(\ell=\min(a,b)\), \(h=\max(a,b)\). Symmetric in the two muscles and non-negative.

"frost"

Frost et al. (1997) variant: the time-average of the instantaneous co-activation ratio \(2\min(a,b)/(a+b)\), as a percentage.

References

Falconer, K. & Winter, D.A. (1985). "Quantitative assessment of co-contraction at the ankle joint in walking." Electromyography and Clinical Neurophysiology, 25(2-3), 135-149.

Rudolph, K.S., Axe, M.J. & Snyder-Mackler, L. (2000). "Dynamic stability after ACL injury: who can hop?" Knee Surgery, Sports Traumatology, Arthroscopy, 8(5), 262-269. doi:10.1007/s001670000130

Frost, G., Dowling, J., Dyson, K. & Bar-Or, O. (1997). "Cocontraction in three age groups of children during treadmill locomotion." Journal of Electromyography and Kinesiology, 7(3), 179-186. doi:10.1016/S1050-6411(97)84626-3

See also

emgEnvelope() for computing amplitude envelopes, emgAmplitudeNormalize() for reference normalization, emgOnsetDetect() for activation timing

Examples

set.seed(1)
t <- seq_len(1000)
a <- exp(-((t - 400) / 120)^2)            # agonist envelope
b <- exp(-((t - 600) / 120)^2)            # antagonist envelope
pe <- PhysioExperiment(
  assays = list(env = cbind(a, b)),
  colData = S4Vectors::DataFrame(label = c("TA", "GAS"),
                                 type = c("EMG", "EMG")),
  samplingRate = 1000)
emgCoContraction(pe, agonist = "TA", antagonist = "GAS")$summary
#> [1] 23.85986