Balance loss when lifting a heavier-than-expected load: Effects of lifting technique  Deborah Givens Heiss, PT, PhD, OCS, Richard K. Shields, PT, PhD, H.John Yack, PT, PhD  Archives of Physical Medicine and Rehabilitation  Volume 83, Issue 1, Pages 48-59 (January 2002) DOI: 10.1053/apmr.2002.27377 Copyright © 2002 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 1 The 2 possible orders of the loads lifted. Loads were based on the percentage maximum lifting capacity. Archives of Physical Medicine and Rehabilitation 2002 83, 48-59DOI: (10.1053/apmr.2002.27377) Copyright © 2002 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 2 Sequences of stick figures representing averaged data at each of 6 points in time for groups 1 and 2. For each stick figure, the solid circles and lines represent group 1, the open circles and dashed lines represent group 2. The first stick figure corresponds to 200ms before 1 newton of upward force is exerted on the load. The GRF vector and body COM are shown on each figure. Symbols above each figure indicate differences (P <.01) between the groups for the magnitudes of the lumbar angle, knee angle, hip angle, and COMy. (A) Subjects expected and lifted a 5% load. The dotted vertical line at t =.04 ±.02 seconds represents the averaged time of load liftoff for both groups. (B) Subjects expected and lifted a 35% load. The dotted vertical line at t =.16 ±.06 seconds represents the averaged time of load liftoff for both groups. (C) Subjects expected a 5% load and lifted a 35% load. The dotted vertical line indicates when the subjects expected the load to liftoff, based on the load magnitude of the previous lift. The solid vertical line at.18 ±.07 seconds indicates the time of load liftoff for group 1. Liftoff for group 2’s first attempt at lifting the load is indicated by the dashed line at.22 ±.06 seconds. Group 2’s second lift started between.40 and.60 seconds. Archives of Physical Medicine and Rehabilitation 2002 83, 48-59DOI: (10.1053/apmr.2002.27377) Copyright © 2002 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 3 Lumbar and lower extremity joint moments over time for the lifts when the load was the same weight as the subject expected, based on the previous lift. The lines and bars represent averaged ± standard error (SE) data for the groups. The dotted vertical line at t =.04 ±.02 second represents the averaged time of liftoff of the 5% load. The solid vertical line at t =.16 ±.06 seconds is the averaged time of liftoff of the 35% load. Archives of Physical Medicine and Rehabilitation 2002 83, 48-59DOI: (10.1053/apmr.2002.27377) Copyright © 2002 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 4 Mean ± SE GRFs under the feet and whole-body momentum over time when the load was the same weight as the subject expected, based on the previous lift. The dotted vertical line indicates the liftoff of the 5% load; the solid vertical line represents liftoff of the 35% load. Archives of Physical Medicine and Rehabilitation 2002 83, 48-59DOI: (10.1053/apmr.2002.27377) Copyright © 2002 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 5 Mean ± SE lumbar and lower extremity joint moments over time when the subject expected a 5% load and lifted a 35% load. The (5)5 lifts are also provided to show that the subjects planned the lift based on the expectation of a light load. The dotted vertical line indicates when the subjects expected the (5)35 load to liftoff, based on the load magnitude of the previous lift. The solid vertical line at.18 ±.07 seconds indicates the time of load liftoff for group 1. The dashed lined at.22 ±.06 seconds indicates liftoff for group 2’s first attempt at lifting the load. Archives of Physical Medicine and Rehabilitation 2002 83, 48-59DOI: (10.1053/apmr.2002.27377) Copyright © 2002 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 6 Mean ± SE GRFs under the feet and whole-body momentum over time when the subject expected a 5% load and lifted a 35% load. The dotted vertical line indicates when the subjects expected the (5)35 load to liftoff, based on the load magnitude of the previous lift. The solid vertical line indicates the time of load liftoff for group 1. The dashed line indicates liftoff for group 2’s first attempt at lifting the load. Archives of Physical Medicine and Rehabilitation 2002 83, 48-59DOI: (10.1053/apmr.2002.27377) Copyright © 2002 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 7 Mean ± SE lumbar angular velocity for groups 1 and 2 during the expected and unexpected 35% lifts over the full lift (−1.0 to 1.0s). The dotted vertical line indicates when liftoff of the (5)35 load was expected, based on the previous lift; the solid vertical line represents liftoff of the (35)35 load. Negative angular velocities indicate flexion of lumbar spine whereas positive angular velocities indicate extension. Archives of Physical Medicine and Rehabilitation 2002 83, 48-59DOI: (10.1053/apmr.2002.27377) Copyright © 2002 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions