Continuous relative phase variability of hand-held load carriage techniques: The effectiveness of a mover's assistive device
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Professional furniture movers must carry objects of all shapes, sizes and weights. When carrying boxes between a house and the moving van, professional movers will carry boxes two different ways. The first way is holding the box in their hands in front of their body, and the second way is holding the box behind them and leaning forward so the box can rest on their backs while walking. The Mover’s Assistive Device (MAD) is an aid developed to decrease the effort of movers when carrying boxes and has been shown to reduce the amount of needed grip strength. The goals of this research were to compare the effects of technique (carrying in front or behind the body) as well as the effects of using the MAD on the way movers coordinate their 1) legs and 2) trunk and hips. Movement was tracked using a camera system and reflective markers attached to the participants. In study 1 ten male participants completed the four different carrying conditions on a treadmill. The different segments of the leg did not change coordination patterns between the front and back carries, however, the coordination was more stable (similar across all steps) in the front carry. When participants used the MAD, their legs moved in a more coordinated motion than when they did not use the MAD, and is considered to be useful in maintaining balance and control while carrying a box. In study 2 thirteen male participants completed the four different carrying conditions on a treadmill. The trunk and the hips did not change coordination between the front and back carries, but they became more coordinated when participants were wearing the MAD. A more coordinated motion between the trunk and hips is suggested to be beneficial to low back health.