Compute work and power output from a work loop experiment on a per-cycle basis.

analyze_workloop(x, simplify = FALSE, GR = 1, M = -1,
  vel_bf = 0.05, ...)



A workloop object of class muscle_stim that has been passed through select_cycles. See Details.


Logical. If FALSE, the full analyzed workloop object is returned. If TRUE a simpler table of net work and power (by cycle) is returned.


Gear ratio, set to 1 by default


Velocity multiplier, set adjust the sign of velocity. This parameter should generally be either -1 (the default) or 1.


Critical frequency (scalar) for low-pass filtering of velocity via signal::butter()


Additional arguments potentially passed down from read_analyze_wl() or read_analyze_wl_dir()


The function returns a list of class analyzed_workloop that provides instantaneous velocity, a smoothed velocity, and computes work, instantaneous power, and net power from a work loop experiment. All data are organized by the cycle number and important metadata are stored as Attributes.

Within the list, each entry is labeled by cycle and includes:


Time, in sec


Length change of the muscle, corrected for gear ratio, in mm


Force, corrected for gear ratio, in mN


When stimulation occurs, on a binary scale


Cycle ID, as a letter


Instantaneous velocity, computed from Position change, reported in meters/sec


Instantaneous velocity, after low-pass filtering, again in meter/sec


Instantaneous power, a product of Force and Filt_velocity, reported in J


The percent of that particular cycle which has elapsed

In addition, the following information is stored in the analyzed_workloop object's attributes:

Frequency at which stimulus pulses occurred


Frequency of oscillations (assuming sine wave trajectory)


Total number of oscillatory cycles (assuming sine wave trajectory) that the muscle experienced.


Specifies what part of the cycle is understood as the beginning and end. There are currently three options: 'lo' for L0-to-L0; 'p2p' for peak-to-peak; and 't2t' for trough-to-trough


Amplitude of length change (assuming sine wave trajectory)


Phase of the oscillatory cycle (in percent) at which stimulation occurred. Somewhat experimental, please use with caution


Logical; whether position inversion has been applied)


The units of measurement for each column in the object after running this function. See Warning


Frequency at which samples were collected


Additional information from the header


Units from each Channel of the original ddf file


Protocol in tabular format; taken from the original ddf file


Specific info on stimulus protocol; taken from the original ddf file


Number of sequential pulses within a stimulation train


Timing offset at which stimulus began


Gear ratio applied by this function


File name


Time at which file was last modified


Which cycles were retained, as numerics


Simple table showing work (in J) and net power (in W) for each cycle


Please note that select_cycles() must be run on data prior to using this function. This function relies on the input muscle_stim object being organized by cycle number.

The muscle_stim object (x) must be a workloop, preferably read in by one of our data import functions. Please see documentation for as_muscle_stim() if you need to manually construct a muscle_stim object from a non .ddf source.

The gear ratio (GR) and velocity multiplier (M) parameters can help correct for issues related to the magnitude and sign of data collection. By default, they are set to apply no gear ratio adjustment and to positivize velocity. Instantaneous velocity is often noisy and the vel_bf parameter allows for low-pass filtering of velocity data. See signal::butter() and signal::filtfilt() for details of how filtering is achieved.

Please also be careful with units! Se Warning section below.


Most systems we have encountered record Position data in millimeters and Force in millinewtons, and therefore this function assumes data are recorded in those units. Through a series of internal conversions, this function computes velocity in meters/sec, work in Joules, and power in Watts. If your raw data do not originate in millimeters and millinewtons, please transform your data accordingly and ignore what you see in the attribute units.


Josephson RK. 1985. Mechanical Power output from Striated Muscle during Cyclic Contraction. Journal of Experimental Biology 114: 493-512.

See also


library(workloopR) # import the workloop.ddf file included in workloopR wl_dat <-read_ddf(system.file("extdata", "workloop.ddf", package = 'workloopR'), phase_from_peak = TRUE) # select cycles 3 through 5 via the peak-to-peak definition wl_selected <- select_cycles(wl_dat, cycle_def = "p2p", keep_cycles = 3:5) # run the analysis function and get the full object wl_analyzed <- analyze_workloop(wl_selected, GR = 2) # print methods give a short summary print(wl_analyzed)
#> File ID: workloop.ddf #> Cycles: 3 cycles kept out of 6 #> Mean Work: 0.00308 J #> Mean Power: 0.08474 W #>
# summary provides a bit more detail summary(wl_analyzed)
#> # Workloop Data: #> #> #> File ID: workloop.ddf #> Mod Time (mtime): 2020-09-16 11:25:43 #> Sample Frequency: 10000Hz #> #> data.frame Columns: #> Position (mm) #> Force (mN) #> Stim (TTL) #> Cycle (letters) #> Inst_Velocity (m/s) #> Filt_Velocity (m/s) #> Inst_Power (W) #> Percent_of_Cycle (NA) #> #> Stimulus Offset: 0.012s #> Stimulus Frequency: 300Hz #> Stimulus Width: 0.2ms #> Stimulus Pulses: 4 #> Gear Ratio: 2 #> #> Cycle Frequency: 28Hz #> Total Cycles (peak-to-peak): 6 #> Cycles Retained: 3 #> Amplitude: 1.575mm #> #> #> Cycle Work Net_Power #> a A 0.002785397 0.07639783 #> b B 0.003147250 0.08661014 #> c C 0.003305744 0.09122522
# run the analysis but get the simplified version wl_analyzed_simple <- analyze_workloop(wl_selected, simplify = TRUE, GR = 2)