Integrate joint power into concentric and eccentric work

Integrates a joint power time series (from computeJointPower()) with the trapezoidal rule to obtain concentric work (integral of positive "generation" power) and eccentric work (integral of negative "absorption" power). Because the trapezoidal rule is linear in the sampled values, concentric_work + eccentric_work equals the net integrated work to floating-point precision. Work can optionally be split per gait cycle or movement phase and normalised to body mass.

Usage

jointWork(power, sampling_rate, body_mass = NULL, windows = NULL)

Arguments

power: Numeric vector of joint power (W), or a data frame with a power column as returned by computeJointPower(..., split = TRUE).
sampling_rate: Sampling rate in Hz.
body_mass: Optional body mass in kilograms; if supplied, mass-normalised work columns (*_per_kg, J/kg) are added.
windows: Optional named list of integer index vectors, each selecting the samples of one gait cycle or phase (e.g. from segmentPhases()). Work is computed independently within each window. If NULL, work is computed over the whole series (window label "full").

Value

A data frame (class joint_work) with one row per window and columns window, concentric_work, eccentric_work, and net_work (J), plus the mass-normalised counterparts when body_mass is given.

References

Winter DA (2009). "Biomechanics and Motor Control of Human Movement." 4th ed. John Wiley & Sons.

Examples

t <- seq(0, 1, length.out = 101)
power <- 100 * sin(2 * pi * t)
jointWork(power, sampling_rate = 100, body_mass = 70)
#>   window concentric_work eccentric_work     net_work concentric_work_per_kg
#> 1   full        31.82052      -31.82052 2.220446e-16              0.4545788
#>   eccentric_work_per_kg net_work_per_kg
#> 1            -0.4545788    3.172066e-18