# Inter-Session Repeatability of Marker-Less Motion Capture of Treadmill Running Gait
## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{8}{c}{**Toe Off**} \\ \hline  & \multicolumn{4}{c}{**Mean (SD) [Deg.]**} & \multicolumn{4}{c}{**ICC\({}_{\text{(Q,I)}}\)**} & \multicolumn{4}{c}{**95\% CI**} & \multicolumn{2}{c}{**SEM**} & \multicolumn{1}{c}{**MDC**} \\  & **Day 1** & \multicolumn{2}{c}{**Day 2**} & \multicolumn{2}{c}{**Day 3**} & \multicolumn{2}{c}{**Lower**} & \multicolumn{1}{c}{**Upper**} & \multicolumn{1}{c}{**[Deg.]**} & \multicolumn{1}{c}{**[Deg.]**} \\ \hline
**Pelvis** & & & & & & & & & & \\ Anterior Tilt & 7.7 & (3.3) & 7.8 & (2.5) & 8.0 & (3.1) & 0.669 & 0.548 & 0.770 & 0.21 & 0.6 \\ Drop & 5.2 & (1.9) & 5.0 & (2.1) & 5.2 & (2.1) & 0.831 & 0.758 & 0.888 & 0.17 & 0.5 \\ lpsilateral Rotation & 0.7 & (3.3) & 1.4 & (3.6) & 1.1 & (3.9) & 0.873 & 0.815 & 0.917 & 0.31 & 0.9 \\
**Trunk** & & & & & & & & & & & \\ Forward Lean & 7.2 & (4.5) & 6.9 & (4.7) & 6.6 & (4.4) & 0.956 & 0.934 & 0.972 & 0.23 & 0.6 \\ Centralateral & 1.9 & (1.3) & 1.8 & (1.5) & 2.4 & (1.3) & 0.835 & 0.762 & 0.89 & 0.17 & 0.5 \\ Flexion & & & & & & & & & & & \\ Centralateral & 15.2 & (3.2) & 15.1 & (3.0) & 15.6 & (3.2) & 0.940 & 0.910 & 0.961 & 0.36 & 1.0 \\ Rotation & & & & & & & & & & & \\ \hline \hline \end{tabular} Note: SD = standard deviation; ICC = intraclass correlation coefficient; CI = confidence interval; SEM = standard error of measurement; MDC = minimal detectable change.  
\end{table} 
Table 5: _Cont._of error [27]. However, with an ML motion capture system, participants can be instructed to maintain footwear between sessions and wear typical running clothes (as in the current study) without increasing measurement variability. [PERSON] et al. [17] reported that clothing choice produced, on average, root-mean-square-differences of 2.6\({}^{\circ}\) within lower extremity joint angles during overground walking while using the same ML motion capture system used in this study. This magnitude exceeded inter-session differences for the current study and highlights that some standardization of clothing (i.e., \"running clothes\") may reduce inter-session variability for TM running. The final objective of the current investigation was to examine the reliability of discrete measures typically reported within research investigations or clinical assessments. Good or excellent agreement was noted in over 70% (30/45) of measures and moderate agreement in 27%. Only peak hip internal rotation excursion during stance demonstrated poor agreement (ICC\({}_{3,1}\) = 0.487) over the three sessions. On average, discrete measures demonstrated good reliability across all planes with sagittal and frontal plane metrics slightly better than transverse plane metrics (ICC\({}_{\text{sagittal}}\) = 0.849, ICC\({}_{\text{frontal}}\) = 0.828, and IC-C\({}_{\text{transverse}}\) = 0.770). [PERSON] et al. [28] reported similar findings (ICC\({}_{\text{sagittal}}\) = 0.788, ICC\({}_{\text{frontal}}\) = 0.833, and ICC\({}_{\text{transverse}}\) = 0.771) in their investigation of the repeatability of TM running using a marker-based motion capture system. In the current study, the transverse plane angles of the ankle and hip had the worst reliability (ICC = 0.618, 0.620) and were lower than values (ICC = 0.759, 0.752) reported by [PERSON] et al. [28]. Measurement of transverse plane angles has been noted as a challenge for ML motion capture with previous investigations reporting reduced performance in their accurate measurement [9; 10]. Overall, an ML motion capture system can reliably measure key discrete metrics of TM running biomechanics over multiple sessions in a manner similar to using a marker-based system. The average SEM for discrete measures at initial contact (0.68\({}^{\circ}\)), peak stance phase angle (0.67\({}^{\circ}\)), and toe off (0.27\({}^{\circ}\)) gave an indication of the precision of an ML motion capture system in assessing kinematics at these events. Additionally, the MDC reported for these metrics is required to ascertain whether biomechanical changes surpass clinical thresholds.