The effect of the stay active advice on physical activity and on the course of acute severe low back pain

Table 1 Linear mixed models to estimate change in step count over seven days follow-up and the effect of treatment advice (SA = Stay active versus AA = Adjust activity) on this change

N = 99	Model 1: Change trajectory		Model 2: Effect of treatment advice
Fixed effects in model	Estimate (SE)	p-value	Estimate (SE)	p-value
Day 1 (intercept)	4434 (405)	<0.001	4317 (558)	<0.001
+Stay active advice	-	-	243 (812)	0.76
Day (β, linear term)	3160 (398)	<0.001	2773 (545)	<0.001
+Stay active advice	-	-	824 (796)	0.30
Day² (β, quadratic term)	−987 (161)	<0.001	−865 (220)	<0.001
+Stay active advice	-	-	−257 (321)	0.42
Day³ (β, cubic term)	94 (18)	<0.001	75 (24)	0.002
+Stay active advice	-	-	34 (36)	0.34

Fixed effects in models are presented with step count as outcome
Model 1 is the estimated change trajectory without the effect of treatment advice. Model 2 includes the effect of treatment advice, where the effect of the Adjust activity is presented first followed by the added effect of the Stay active advice
A third-order polynomial function was used with a linear term (Day) describing the initial increase (positive value), a quadratic term (Day²) describing the level-off of the initial increase (negative value) and a cubic term (Day³) for the additional final increase in step count over time

ISSN: 2052-1847