Does the personal lift-assist device affect the local dynamic stability of the spine during lifting?

Local dynamic stability of the lifting kinematic chain

“…Subjects performed 30 continuous, symmetrical, freestyle box lifts with their feet stationary (10/min) from a target on the floor to a target on a table top, which was set at 50% of their standing height. The load lifted was equivalent to 10% of each participant's maximum back strength; established previously [6][7][8]. The average load lifted was 6.93(AE0.72) kg for males, and 4.8(AE0.65) kg for females.…”

“…Participants' mean age, height, and weight were 24.2(AE2.9) years, 184.9(AE7.6) cm and 85.4(AE10.7) kg for males; and 23.0(AE2.6) years, 170.1(AE6.1) cm and 66.3(AE11.7) kg for females. The lifting protocol is described elsewhere in detail [6][7][8]. Subjects performed 30 continuous, symmetrical, freestyle box lifts with their feet stationary (10/min) from a target on the floor to a target on a table top, which was set at 50% of their standing height.…”

“…Six infrared emitting diode (IRED) marker triads were located laterally on each subject's right foot, shank, and thigh, as well as on custom-made fins projecting from S 1 , T 12 , and C 7 . Custom Matlab software (The MathWorks, Natick, MA, USA) was used for all data processing [6,7].…”

“…Linear motions were defined using the origin of each coordinate system, whereas 3D rotations were defined using a tilt-obliquity-rotation convention relative to the laboratory global coordinate system [5]. Both linear and angular data were then filtered using a 10 Hz low-pass second-order digital Butterworth filter [5][6][7]9], and converted to velocities to reduce non-stationarities in the displacement data [5,10]. The last 25 lifts were extracted to ensure a steady-state movement pattern [9], and the data were time normalized to a constant number of data points (15,000) as the number of samples can affect stability analyses [11].…”

“…finite-time Lyapunov exponents (l max-s and l max-l ) were then calculated using standard methods to quantify the local dynamic stability of each segment in the kinematic chain [5][6][7]9,14] (Fig. 1).…”