Table 1.

Dynamic sagittal balance metrics

Variable name	Variable definition	Scaling variable	Units
Time	Time between quiet sitting and quiet standing. Quiet sit and stand are the last and first time points where the subject is in a seated or standing position and the energy of the torso is effectively zero	None	s
Peak SVA	Peak sagittal distance between the hip and shoulder centers	Height	None
Horizontal and vertical momentum	The horizontal and vertical momenta of the torso as seen in the world frame	Height*Mass	1/s
Torque at the lower lumbar spine, hip and knee	Peak estimated torque at the L5/S1, hip, and knee joints	Height2*Mass	1/s2
Sacral compression and shear	Peak compressive and shear forces at S1 based on the musculoskeletal model from Chaffin et al. (2006)	Height*Mass	1/s2
Spinal extensor muscle force	Peak contractile force on the back extensor muscles based on musculoskeletal model from Chaffin et al. (2006)	Height*Mass	1/s2
Flexion and extension of the hip and knee	Maximum flexion and extension angles of hip and knee joints	None	°
Total motoric energy of the hip and knee	Integral of the instantaneous power by time over the whole STS action	Height2*Mass	1/s2
Dynamic CoP	Maximum sagittal distance from the center of the foot to the CoP	Subject foot length (from allometric scaling)	None
Standing CoP	Distance from the center of the foot to the CoP during quiet standing	Subject foot length (from allometric scaling)	None