Table 3.

Analysis of breathing during initial experimental conditions.

Dependent variable	Comparison	Estimate	SE	z	p-value
${\dot{V}}_E$ (ln-transformed)	R vs. U	0.27	0.03	11.17	< 0.0001
	${\text{W}}_1$ vs. R	− 0.14	0.03	− 4.58	< 0.0001
$\mathrm{\Delta }$FRC	R vs. U	− 0.35	0.01	− 32.67	< 0.0001
	${\text{W}}_1$ vs. R	0.18	0.02	10.38	< 0.0001

The mixed-effects regression models used to test these contrasts accounted for a subject’s age, their BMI, and the experimental phase in the fixed effects, and included a random effect of subject identity to account for repeated measures (n = 911 breaths from 17 subjects in phases R, U, and ${\text{W}}_1$). To appropriately model the variances, ${\dot{V}}_E$ was ln-transformed, and the analysis for $\mathrm{\Delta }$FRC accounted for unequal variance across phases. The table provides test statistics for post-hoc contrasts of specific comparisons. U = initial standing upright measurement; R = unweighted prone measurement; ${\text{W}}_1$ = first minute of weighted prone measurement.