Fig. 2: Elbow torque estimation during isokinetic contractions of the biceps brachii.

A Illustration of participants secured on a dynamometer with SETs placed over the BB muscle belly. B Example elbow angle, elbow torque, and BB thickness from a representative participant during passive (pass; gray), concentric (conc; red), and eccentric (ecc; blue) contractions at 60° s⁻¹, 90° s⁻¹, and 120° s⁻¹. Lines and shaded regions represent mean ± SD (n = 7 contractions). C Example relationship between BB thickness, elbow angle, and elbow torque from a representative participant across all conditions, with an overlaid quadratic fit (gray). D RMSEs for different contraction speeds across all participants (n = 10). One-way ANOVA: no significant main effect (p = 0.851, F_2,18 = 0.163). E RMSEs for different contraction types across all participants (n = 10). One-way ANOVA: significant main effects (p < 0.001, F_2,18 = 35.0). Bonferroni post-hoc analysis: pass vs conc (p < 0.001), pass vs ecc (p < 0.001), and conc vs ecc (p = 0.527). For D and E, each box bounds the interquartile range (IQR) divided by the median with whiskers extending up to 1.5*IQR. Each dot represents the RMSE for one participant. *p < 0.05.