Readme file for data used in study:
"Evidence for a Time-Invariant Phase Variable in Human Ankle Control"
R D Gregg, E J Rouse, L J Hargrove and J W Sensinger
PLOS ONE
For questions regarding the data, please contact the authors:
Robert Gregg (rgregg@utdallas.edu) or Elliott Rouse (erouse@media.mit.edu)
Please see the methods section of the aforementioned scientific paper for an in-depth description of how the data were collected. For the benefit of this readme file, the methods will be briefly described. The data contained herein includes kinetic and kinematic data acquired during walking trials, while a subject walked a across a walkway. A perturbation device was recessed into the walkway and randomly applied a two or five degree incline perturbation to the ankle as subjects walked across the platform. The perturbations occurred at one of four timing intervals, namely 100, 225, 350 and 475 ms following heel strike. During each trial, subject ankle angle and ground reaction force data were acquired, including location of the center of pressure for each subject.
The data are organized as a separate folder for each perturbation magnitude (two or five degrees), with each folder containing a Matlab data file (The Mathworks, Natick, MA) for each subject. The Matlab data files (.mat) are named according to the subject abbreviation used in the study. Each .mat file includes the following variables, acquired from a Kistler force platform (model: 9260AA3, Winterthur, Switzerland) via a National Instruments 16-bit data acquisition card (model: USB-6218, Austin, Texas) and a Delsys electrogoniometer (Boston, MA) sensing ankle angle. All data were acquired with a sample rate of 1 kHz and filtered with a bi-directional fourth-order Butterworth filter with a cut-off frequency of 20 Hz.
The inner struct level for many variables includes 'dorsi' and 'plantar.' This defines whether the data were acquired from a dorsiflexive or plantarflexive perturbation. The distinction PERT is used to generically represent both perturbation directions. Additionally, each perturbation timing point is delineated with a '100' - '475.' This number denotes the number of milliseconds following heelstrike the perturbation occurred. The distinction TIMEPOINT is used to generically represent the set of perturbation timing options.
Data are presented for normalized and non-normalized ankle angle for each trial. Normalization (denoted as level 'HCref') indicates that the angle was zeroed upon heelstrike. This normalization removes any bias associated with the mounting of the electrogoniometer. Non-normalized, raw ankle angles are denoted without the 'HCref' notifier (or as 'abs'). The distinction NORM will be used to generically represent both normalized and non-normalized data options.
All data begin at heel contact and end after 850 ms (with one sample per ms).
- COP_SPlane_NoPert: matrix containing 850 samples of approximately 400 trials. Trials are denoted as columns. This matrix is the sagittal plane displacement of the center of pressure (COP) with respect to the ankle's center of rotation. In other words, a COP displacement of zero would indicate that the COP is directly below the ankle’s center of rotation. Dimensions are in meters.
- COP_SPlane_TIMEPOINT: Matlab struct containing PERT levels, with each level containing a matrix with 850 samples of approximately 50 trials. Trials are denoted as columns. This matrix is the sagittal plane displacement of the center of pressure (COP) with respect to the ankle's center of rotation. In other words, a COP displacement of zero would indicate that the COP is directly below the ankles center of rotation. Dimensions are in meters.
- Foot_Shank_Ang: Matlab struct containing NORM levels. Each level contains a matrix that is 850 samples of approximately 400 trials. Trials are denoted as columns. These matrices represent the ankle angle profile during non-perturbed trials. Dimensions are in degrees.
- Foot_Shank_Ang_TIMEPOINT: Matlab struct containing PERT x NORM levels. Each level contains a matrix that is 850 samples of approximately 50 trials. These matrices represent the ankle angle profile during non-perturbed trials. Dimensions are in degrees.
- Pert_Data_TIMEPOINT: Matlab struct containing PERT levels. Each level contains a matrix that is 850 samples by approximately 50 trials. Trials are denoted as columns. These matrices contain the angle of the perturbation platform. Dimensions are in degrees.
- X_Force: matrix containing 850 samples of approximately 400 trials. Trials are denoted as columns. This matrix is the x-axis (anterior - posterior) component of the ground reaction force for non-perturbed trials. Dimensions are in Newtons.
- X_Force_TIMEPOINT: Matlab struct containing PERT levels, with each level containing a matrix with 850 samples of approximately 50 trials. Trials are denoted as columns. These matrices are the x-axis (anterior - posterior) component of the ground reaction force for non-perturbed trials. Dimensions are in Newtons
- Z_Force: matrix containing 850 samples of approximately 400 trials. Trials are denoted as columns. This matrix is the z-axis (inferior - superior) component of the ground reaction force for non-perturbed trials. Dimensions are in Newtons.
- Z_Force_TIMEPOINT: Matlab struct containing PERT levels, with each level containing a matrix with 850 samples of approximately 50 trials. Trials are denoted as columns. These matrices are the z-axis (inferior - superior) component of the ground reaction force for non-perturbed trials. Dimensions are in Newtons