Fig. 8

Calibration performance across all participants by using three HNM categories. The mean and SD of \(BM-RMSE\), \(N-RMSE\), and \(R^{2}\) values across all participants under both single-speed modes and inter-speed mode are displayed in upper, middle, and lower plots, respectively, during calibration procedures. Blue, red, and yellow bars represent the results by using sEMG-, US imaging-, and sEMG-US imaging-driven HNMs, respectively. Letters and asterisks represent the statistically significant difference from the two-way repeated-measure ANOVA followed by a Tukey’s HSD, where letters stand for the evaluation of the walking speed factor (significant difference only exists between each two bar groups out of the left six groups without any overlap of letters) and asterisks stand for the evaluation of the applied HNM type factor (significant difference exists between each two bars out of the most right group when the asterisk is there)