Muscle mediates movement but movement is typically unsteady and perturbed. Muscle is known to behave non-linearly and with history dependent properties during steady locomotion, but the importance of history dependence in mediating muscles function during perturbations remains less clear. To explore muscle's capacity to mitigate perturbations during locomotion, we constructed a series of perturbations that varied only in kinematic history, keeping instantaneous position, velocity and time from stimulation constant. We find that muscle's perturbation response is profoundly history dependent, varying by four fold as baseline frequency changes, and dissipating energy equivalent to  ~6 times the kinetic energy of all the limbs in 5 ms (nearly 2400 W Kg^-1). Muscle's energy dissipation during a perturbation is predicted primarily by the force at the onset of the perturbation. This relationship holds across different frequencies and timings of stimulation. This history dependence behaves like a viscoelastic memory producing perturbation responses that vary with the frequency of the underlying movement. 

The necessary methods are included in the manuscript.

The data files include a set of folders and raw recordings for force, length, stimulation, and other associated parameters. The highest level folder structure organizes the data first into collection days. Within each day are the data recording files. There are two types of files.

1) *.csv files contain the data for the specific trial. There are four labeled columns containing time (sec), displacement (mm), force (mN), and stimulation (V).

2) *_parameters.txt files contain the settings for each specific trial. Each .csv file has a correspondings parameters files that can imported or queried.

The naming convention is D_[data in YYYYMMDD]_[animal number for that day]_[trial type]_[trial number]

The [trial types] are:

1)"freq_effect", which tests changing the background strain frequency or history of the muscle

2) "isometric_twitch" which has data for isometric twitches

3) "workloop_controls" which includes control workloops at different points in the experiment 

4) "timing_effect" which captures the effect of changing the timing of stimulation prior to perturbation.

Not all trial numbers are contiguous becuase occasionally a spurious recording was made or a data was dropped.