Common use of Experiment Clause in Contracts

Experiment. 93 As in previous studies (3, 14), participants stood barefoot on two laboratory-grade force plates 00 (XXXX-XX0-0-0000, XXXX, Xxxxxxxxx, XX, XXX). The force plates were mounted onto a custom 95 translation platform; however, analyses here considered only periods during which the platform was 96 stationary. Force and moment data were sampled at 1080 Hz and used to calculate the locations of the 97 center of pressure beneath each foot using calibration values supplied with the plates (15-17). Kinematic 98 data were collected at 120 Hz using a Vicon motion capture system (Centennial, CO, USA) and a 25- 99 marker set including reflective markers placed on the left and right heels. Average foot CoP locations and 100 heel marker positions were calculated over the first 250 ms of each trial. 101 Stance width was controlled by requesting participants press an object (typically a book) between the 102 medial surfaces of their feet, which was subsequently removed before data collection (≈87% of trials), or 103 by manipulating participant’s feet so that kinematic markers on the heels were aligned in the mediolateral 104 direction with tape marks on the floor (≈13%). 105 2.3 DATA ANALYSIS 106 Stance width measurements derived from CoP and kinematic data were plotted against each other and 107 examined visually. After visual assessment of outliers, trials were excluded due to: 1) tension in a ceiling- 108 mounted fall arrest tether interfering with CoP calculation (17 trials in one participant), and 2) absent 109 video records preventing trial review (2 trials in one participant). After applying exclusions, 1363 trials 110 (41 – 161 per participant) were available for analysis. Stance widths were expressed in mm and 111 normalized to inter-ASIS distance. 112 Following Xxxxx and Xxxxxx (10), correlation between the two measurements was assessed with the 113 Xxxxxxx product-moment correlation coefficient r. Differences between methods were calculated for each 114 trial and averaged across trials into a single difference value di for each participant. Mean values across 115 methods were calculated for each trial and averaged into a single mean value mi for each participant. Bias 116 between the two methods was quantified as the mean difference d (CoP – kinematic method) and the 117 standard deviation of the differences s. The limits of agreement were calculated as the range d–2s to d+2s. 118 Variation of differences di across groups was assessed with one-way ANOVA. Associations between 119 differences di and mean values mi were assessed with r (12). Data processing was performed in Matlab 120 (r2016b, The Mathworks, Natick, MA, USA). Statistical procedures were performed in SAS Studio (3.5, 000 Xxx XXX Xxxxxxxxx, Xxxx, XX, USA) and considered significant at P = 0.05. 122 3. Results 123 Stance widths measured from kinematic data varied between 75 – 348 mm, corresponding to 24.9 – 124 154.1% of inter-ASIS distance. CoP and kinematic stance width measurements are presented in Figure 125 1A. The two measures were strongly correlated (r = 0.98). The mean difference d between methods was 126 48 mm, and the standard deviation of the differences (s) was 17 mm. Differences di did not vary across 127 groups (F2,12=1.81, P<0.21). The limits of agreement, defined as the range d–2s to d+2s (10), was 14–83 128 mm. A “Xxxxx-Xxxxxx plot” of the differences between the two methods di against their means mi is 129 presented in Figure 1B. di and mi were significantly negatively correlated (r = –0.59, P<0.02). 130 4. Discussion 131 Stance width is an important variable in many studies of parkinsonian (4, 5) and neurotypical (18, 19) 132 posture and balance. We found that stance width estimates from foot CoP and kinematic markers were 133 strongly linearly correlated, and that on average, measures of stance width derived from CoP were 48 mm 134 wider than those derived from kinematic markers. This bias that can be explained by the externally- 135 rotated “toe out” posture used by most participants, in which a substantial portion of the foot plantar 136 surface lies lateral to the posterior face of the heel. Overall, these results suggest that foot CoP location, a 137 commonly calculated variable in clinical biomechanics studies (5, 7, 8) can be used to approximate stance 138 width in healthy aging and in individuals with PD in the ON and OFF medication states. 139 We noted that differences between methods were non-negligible – ranging from 14 to 83 mm. 140 However, this precision is adequate to discriminate between nominal stance widths used in the literature, 141 which are typically separated by 100 mm or more (4, 18). Due to the high precision of CoP calculation 142 with laboratory force plates (2-5 mm (17)), the primary source of variability in differences is probably 143 trial-to-trial variability in weight distribution, rather than instrumentation error. 144 There are two notable limitations to this approach. First, differences between methods were highest at 145 the narrow stance widths preferred by PD subjects, a fact that should be considered carefully during study 146 design. Second, because these participants were allowed to adopt a comfortable “toe out” orientation 147 during testing, the agreement between the methods in experimental paradigms in which foot orientation is 148 enforced (e.g., parallel (4); 20° (18)) remains to be established.