A dynamical systems analysis of assisted and unassisted anterior and posterior hand-held load carriage.

Load carriage is recognised as a primary occupational factor leading to slip and fall injuries, and therefore assessing balance maintenance during such tasks is critical in assessing injury risk. Ten males completed 55 strides under five carriage conditions: (1) unassisted anterior, (2) unassisted posterior, (3) assisted anterior, (4) assisted posterior and (5) unloaded gait (UG). Kinematic data were recorded from markers affixed to landmarks on the right side of each participant, in order to calculate segment angles for the foot, shank, thigh and pelvis. Continuous relative phase (CRP) variability was calculated for each segment pair and local dynamic stability was calculated for each segment in all three movement planes. In general, irrespective of the assistive device or movement plane, anterior load carriage was most stable (lower CRP variability and maximum finite-time Lyapunov exponents). Moreover, load carriage was less dynamically stable than UG, displaying the importance of objectively investigating safe load carriage practices. PRACTITIONER SUMMARY: Dynamical systems analyses were used to comprehensively evaluate the stability of various handheld load carriage methods. In general, anterior load carriage was significantly more stable than posterior load carriage,Mover's assistive device had small but beneficial effects on stability, and load carriage was less stable than UG.

The effect of an on-body assistive device on transverse plane trunk coordination during a load carriage task.

Load carriage is a physically demanding task that is often required of employees in many different occupations. The Mover's Assistive Device (MAD) is an on-body ergonomic assistive device designed to help professional movers transfer boxes during two techniques of hand-held load carriage: anterior carriage and posterior carriage. The purpose of this study was to examine the intersegment coordination between the trunk and pelvis as well as the trunk and box, since coordination may be a mechanism to reduce the amount of stress exerted on the back during load carriage. Thirteen males completed a hand-held load carriage task in a laboratory setting using two popular techniques employed by professional movers (anterior/posterior), with and without the assistance of the Mover's Assistive Device (MAD); resulting in a total of four conditions. Triads of retro-reflective markers tracked the angular positions of the trunk, pelvis and the load being carried. Intersegment coordination between the trunk-pelvis and the box-trunk were measured using continuous relative phase angles in the transverse plane of motion. No trunk coordination differences were observed across carrying techniques (anterior/posterior); however, under all conditions users walked with a near in-phase coordination pattern, which is believed to help reduce the risk of injury. MAD use resulted in decreased perceived discomfort and more in-phase coordination between the trunk-pelvis, which may help reduce injury risk when carrying loads either anteriorly or posteriorly.

Interjoint coordination and the personal lift-assist device.

It has been suggested that interjoint coordination may serve to reduce joint stress and muscular demand and to maintain balance during dynamic lifting tasks, thus having implications for safe lifting practices. Before recommending the use of an on-body ergonomic aid, the Personal Lift-Assist Device (PLAD), it is important to determine any effects this device may have on interjoint coordination. Principal component analyses were applied to relative phase angle waveforms, defining the hip-knee and lumbar spine-hip coordination of 15 males and 15 females during a repetitive lifting task. When wearing the PLAD, users lifted with more synchronous hip-knee and lumbar spine-hip coordination patterns (P < .01). Furthermore, increases in load caused less synchronized interjoint coordination at both the hip-knee and lumbar spine-hip during the up and down phases of the lift (P < .01) for all conditions. No significant main effects of sex or significant interactions were observed on any of the outcome variables.