Research Overview – This research was conducted by Payam Mirshams Shahshahani and James A. Ashton-Miller. The project explores how limitations on maximum hip abduction strength and ankle inversion/eversion strength affects one's ability to maintain a quasistatic OLB state and to recover balance from an initial quasistatic state. A modeling approach with a double inverted pendulum was used, and the file provided here allow replication of the results provided in the PLoS ONE paper titled ('On the importance of the hip abductors during a clinical one legged balance test:a theoretical study'). This research was part of the disseration of Payam Mirshams Shahshahani in his PhD from 2013 to 2019. He did his PhD in the Biomechanics Research Lab at the Mechanical Engineerin Department at the University of Michigan Ann Arbor. The funding for this work was provided by NIH the details of which can be found in the manuscript.

Methods – Details can be seen in the Methods section of the manuscript and the supplementary information. MATLAB and R were used to run the simulations of the double inverted pendulum model that we used to represent a person standing on one leg.

File Inventory –
COMstate.m: MATLAB function that receives the states of the double inverted pendulum (vector "X" = [Theta1, Theta2, Theta1dot, Theta2dot]) and anthropometric information (structure "Anth") and returns the states of the center of mass. This function is used in the FBRrun.m script.
Damping.m: MATLAB function that receives the states of the double inverted pendulum (vector "X" = [Theta1, Theta2, Theta1dot, Theta2dot]) and information about the end of range of motion for the ankle and hip in the frontal plane (structure "Cap") and returns the damping term. Used in the EOMwPassiveMinEffort.m function.
EOMwPassiveMinEffort.m: MATLAB function that embedding the equations (ordinaty differential equation) for the double inverted pendulum model to be simulated using the ode45 function in the FBRrun.m script. It takes in time (=t), current states (X), Anthropometric information (= Anth), end of range of motion (Cap), required ankle and hip moments for maintaining the initial state quasistatically (=Treq), span of time simulation should run (=tspan), time it takes to develop half of the maximum joing moment starting from zero (=Time2Half), and initial state (X0)
FBR-ActiveOnly.R: An R script that draws the active feasible balance region (Fig. 2 in the manuscript) based on the provided maximum ankle and hip strengths and anthropometry, 
FBRrun.m: A MATLAB script that calculates the active FBR, net FBR, and recoverable initial quasistatic states (Fig. 5 in the manuscript) and saves the relative data to be used for visualization in Visualize.m
FBR-wPassive.R: An R script that draws the net feasible balance region (Figs 3-4 in the manuscript) based on the proveded maximum ankle and hip strengths, anthropometry, and the assumed passive hip abduction moment.
MyEvents.m: A MATLAB function that determines if ankle end of range of motion has reached in the simulation which would then terminate ode45 execution inside FBRrun.m.
Visualize.m: A MATLAB script that takes in the results of the simulations from FBRrun.m and draws avtive FBR, net FBR, and the recoverable initial quasistatic states for the double inverted pendulum model of one-legged balance (Fig.5 in the manuscript) 

Definition of Terms and Variables – Please refer to the manuscript for a full list of terms and variables.

Use and Access – By running the FBRrun.m script a dataset will be generated and saved. The saved dataset then can be used to run the Visualize.m script which will make the plot used in Fig. 5 of the manuscript. The two R files can be run as is to create Fig. 2-4 in the manuscript.

Informed consent – Not Applicable.