Inter-individual variability in a repetitive lifting task

Trunk kinematics directly impact the biomechanical loading of the tissues of the low back. Quantifying the variability in trunk kinematics may provide deeper insights into biomechanical loading and low back injury risk. Inter-lifter variability in trunk kinematics was assessed as twenty participants performed a repetitive lifting task at three levels of the NIOSH Lifting Index. Trunk kinematics were captured and Levene’s test of homogeneity of variance was used to test the hypothesis that variance in kinematic parameters increased as a function of level of lifting index. Results showed considerable levels of variability in all kinematics parameters, and for sagittal range of motion, mean sagittal velocity, transverse range of motion, and mean transverse velocity the variance was significantly affected (p<0.05) by level of lifting index. The results of this study demonstrate that variability (both inter- and intra-lifter) should be considered as one considers the relative risk of a lifting task.

Body-powered variable impedance: An approach to augmenting humans with a passive device by reshaping lifting posture

The movement patterns appropriate for exercise and manual labor do not always correspond to what people instinctively choose for better comfort. Without expert guidance, people can even increase the risk of injury by choosing a comfortable posture rather than the appropriate one, notably when lifting objects. Even in situations where squatting is accepted as a desirable lifting strategy, people tend to choose the more comfortable strategy of stooping or semisquatting. The common approach to correcting lifting posture, immobilizing vulnerable joints via fixation, is insufficient for preventing back injuries sustained from repetitive lifting. Instead, when lifting small but heavy objects, the entire kinetic chain should cooperate to achieve a series of squat-lifting patterns. Inspired by the observation that force fields affect the coordination of voluntary human motion, we devised a passive exosuit embedded with a body-powered variable-impedance mechanism. The exosuit adds impedance to the human joints according to how far the wearer’s movement is from the squat-lifting trajectories so that it hinders stooping but facilitates squatting. In an experiment that entailed lifting a small 10-kg box, 10 first-time users changed their voluntary lifting motion closer to squatting on average. Simulation results based on recorded kinematic and kinetic data showed that this postural change reduced the compression force, shear force, and moment on the lumbosacral joint. Our work demonstrates the potential of using an exosuit to help people move in a desirable manner without requiring a complicated, bulky mechanical system.

The Effect of an on Body Personal Lift Assist Device (Jaipur Belt) on Trunk Muscle Fatiguability During a Repetitive Lifting Task in Manual Material Handlers – A Non-Randomized Single-Group Trial

Background: An on body personal lift assist device (OBPLAD) is a non-motorized, passive device in which the elastic elements act as an external muscle power generator to assist lifting thereby offloading the trunk muscles. Though there is enough evidence for the use of OBPLAD generated through laboratory studies, we found a scarcity of evidence on the use of OBPLAD in real-life work settings, especially in the Indian population. This study investigates the effect of the Jaipur belt, an OBPLAD, on trunk muscle fatiguability while performing repetitive lifting task in manual material handlers. Methods:70 subjects engaged in manual material handling were recruited from industries in and around Mangalore, Karnataka in this non-randomized single group trial. Subjects were made to perform a repetitive lifting task over a period of 15 minutes with and without an OBPLAD. Electromyographic data were recorded from rectus abdominis, transverse abdominis, quadratus lumborum, and erector spinae from either side of the body, and the onset of fatigue was deduced from the changes in electromyographic parameters. Results: We found a delay in the onset of fatigue in all the muscle groups studied while the lift was performed wearing the Jaipur belt. However, the findings were statistically significant only for right erector spinae, right rectus abdominis, left transverse abdominis, and left quadratus lumborum. It was found also that number of repetitions as well as time for which a task would be sustained were both found to be significantly better wearing an OBPLAD.Conclusion: The findings of the study imply that the Jaipur belt could potentially delay the onset of fatigue in the trunk muscles while performing repetitive lifting task and hence, is proved to be useful in the prevention of fatigue-related musculoskeletal disorders of the lower back.CTRI Registration date: 10/02/2020 Trial registration number: CTRI/2020/02/023219