Table 4. Mean (SD) lumbar (α _lumbar) and thoracic curvature angle (α _thoracic) in the upright, flexed and extended sitting positions calculated with the vertebral bodies and the skin marker, as well as the mean differences (SD; RMSE) between the values from the skin marker and the vertebral bodies.

	Upright		Flexion		Extension
	Vertebral bodies	Marker	Vertebral bodies	Marker	Vertebral bodies	Marker
	Difference		Difference		Difference
αlumbar [°]	−16.8 (11.5)	0.3 (4.3)	−7.9 (13.2)	9.4 (12.6)	−27.7 (7.3)	−5.9 (14.2)
	17.1 (8.0; 18.6)		17.3 (11.2; 20.2)		21.8 (8.1; 22.9)
αthoracic [°]	36.0 (12.4)	40.7 (10.0)	34.4 (10.2)	38.5 (10.1)	28.7 (10.9)	27.9 (9.4)
	4.7 (11.4; 11.5)		4.0 (9.4; 9.5)		−0.8 (8.3; 7.8)