**3. Results**

Legends: US—Unexpected Slip, ES1—Expected Slip Trial 1, ES2—Expected Slip Trial 2, ES3—Expected Slip Trial 3, UT—Unexpected Trip, UT1—Unexpected Trip Trial 1, UT2—Unexpected Trip Trial 2, UT3—Unexpected Trip Trial 3.

Results from both the motion capture data and the SRS data were used to identify ankle joint ROM change from base angle to peak angle and change in capacitance from the base angle position to peak angle position. A series of violin plots are used to present the observed data from the slip and trip trials for all ten participants. The violin plots provide curved areas for each of the slip and trip trials that provides an idea of the "spread" of the data. These violin plots represent a kernel density distribution portrayed vertically. A greater horizontal width of a curve in the plot indicates a greater portion of participants that produced results near the value on the y-axis [24]. Additionally, the presented individual participant data points reiterate the "spread" of the data, so that outliers can be easily identified as well.

In Figures 6 and 7, the average and spread of ankle ROM and peak ROM in plantarflexion for slip trials and dorsiflexion for trip trials are presented respectively. Figures indicate the behavior of ankle joint movement going into plantar flexion during slip perturbations and going into dorsiflexion during trip perturbations. In Figure 8, the average and spread of capacitance change for each foot across every slip and trip trial are presented, to demonstrate the sensor output data.

**Figure 6.** Spread and average ankle range of motion change for each foot across every trial; note that positive and negative changes occur respective to the trial with negative values indicating movement of ankle into PF and positive values indicate movement of ankle into DF.

**Figure 7.** Spread and averages peak angles for each foot across every trial; note that positive and negative changes occur respective to the trial with negative values indicating movement of ankle into PF and positive values indicate movement of ankle into DF.

**Figure 8.** Spread and averages of capacitance change for each foot across every trial.

Results from the study are also presented in different pictorial representations indicating the performance of each trial based on adjusted R-squared and RMSE values (Figure 9; Figure 10). Average adjusted R-squared and average RMSE were identified for determining a relative and absolute goodness of fit of the model for the comparison of motion capture change in ankle angles versus the change in capacitance for all trials. On average, all trials had greater adjusted R-squared values and lower RMSE values in the linear model for the goodness of fit (Figures 9 and 10). Based on the violin plots in Figures 9 and 10, a greater portion of participants produced an R-squared value of more than 0.75 (moderate to high accuracy) and a greater portion of participants produced a RMSE value of lower than 4 (minimal errors). For the left foot–ankle kinematic detection, the highest adjusted R-squared value was 0.9781 (average = 0.7658) and the lowest RMSE was 1.0638 degrees (average = 3.1319 degrees). For the right foot–ankle kinematic detection, the highest adjusted R-squared value was 0.9832 (average = 0.7362) and the lowest RMSE was 0.8176 degrees (average = 0.9832 degrees). Results from the study demonstrated that 71.25% of the trials exhibited a minimal error of 4.0 degrees difference from the motion capture system and a greater than 0.60 R-squared value in the linear model, suggesting a moderate to high accuracy and minimal errors in comparing SRS with a motion capture system.

**Figure** 

**9.** Spread, average, and individual data points of R-squared values for each trial across

 feet.

**Figure 10.** Spread, average, and individual data points of RMSE values for each trial across feet.
