Muscle Contributions to L_4-5 Joint Rotational Stiffness following Sudden Trunk Flexion and Extension Perturbations

Table 1

Summary of the mean and standard deviations of the joint angle and acceleration magnitudes prior to (BL time period) and following the perturbations (VOL time periods). The BL angles and accelerations were calculated as the average magnitudes during that time period, whereas the peak magnitudes found during the VOL time period are reported.

Measure	Trunk			L4-5
	Axis	BL	VOL	BL	VOL
Joint angle (degs)	Flex/Ext	3.7 ± 2.3	5.6 ± 2.5	0.7 ± 0.8	1.1 ± 0.9
	Lat. bend	1.8 ± 1.1	2.3 ± 1.0	0.2 ± 0.1	0.2 ± 0.1
	Twist	1.3 ± 1.1	2.0 ± 1.1	0.1 ± 0.1	0.2 ± 0.1
Joint acceleration (degs/s/s)	Flex/Ext	7.1 ± 27.8	336.3 ± 122.7	1.2 ± 5.8	51.7 ± 31.8
	Lat. bend	3.8 ± 4.5	70.3 ± 25.0	0.4 ± 0.5	7.5 ± 2.7
	Twist	5.8 ± 6.2	66.8 ± 23.4	0.6 ± 0.7	7.4 ± 2.6