Biomechanical Assessment of Varied Lifting Tasks With and Without Passive Back Support Exoskeletons

Low back pain is the number one cause of disability in the world. It is a well established problem in industry often caused by excessive repetition, awkward postures, and heavy lifting. Back support exoskeletons have increasingly been studied as a solution to this problem. In addition to evaluating exoskeletons, giving some focus to the various lifting styles themselves can also provide some insight into ameliorating this problem. Research evaluating warehouse workplace postures has found that workers switch between a variety of tasks and many different lifting styles, beyond the standard squat and stoop postures, on a daily basis.

This dissertation is primarily a compilation of three papers. The first focuses on the VTLowe's exoskeleton and the kinematic differences found during Stoop, Squat, and Freestyle lifting. These lift styles were evaluated while the study participants lifted boxes weighing 0% or 20% of their body weight both With and Without the exoskeleton. Evaluating the kinematic results showed that wearing the exoskeleton resulted in a 1.5 degree increase in ankle dorsiflexion, a 2.6 degree decrease in knee flexion, and a 2.3 degree decrease in SHK angle. Subjects' shoulder, elbow, and wrist heights were slightly higher while wearing the exoskeleton, and they lifted slightly more slowly while wearing the exoskeleton. Subjects moved more quickly while bending down as compared to standing up, and with the 0% bodyweight box as compared to the 20% bodyweight box. The values for Freestyle lifts generally fell in between Squat and Stoop lift styles or were not significantly different from Squat. EMG data (analyzed in a different study) from the leg muscles had relationships with torso torque while the back and stomach muscles showed no significant relationships.

Exoskeleton efficacy research has a strong focus on Stoop, Squat, and Freestyle lifting. However, asymmetric styles such as One Legged lifting and Kneeling were found to be frequently used lifting styles in a warehouse setting. The second paper in this dissertation focuses on variations of asymmetric lifts while lifting light objects including Split Legged, Heel Up, One Legged, Kneeling, Asymmetric Squat, Bent Over (a freestyle task) and Bend Walk (picking up bean bags from the ground while walking forward and maintaining a bent over posture). These lift styles can be found not only in industry, but in any individual's daily life such as when it comes to picking up a dropped pen or sorting toys in a bin on the floor. Evaluating Split Legged, Heel Up, and One Legged found that many of the significant differences in muscle activity are dependent on the lifting stance (whether the front foot is on the same side or opposite side as the hand used to pick up objects). Combining the results that same side lifts have greater muscle imbalance in the iliocostalis and overall back muscle activity is greater in Split Legged than in Heel Up or One Legged suggests that One Legged or Heel Up in an Opposite side stance are the best options in regards to minimizing back muscle activity. Although there is a trade-off with the biceps femoris for these lift styles, back injuries are far more prevalent and supporting the back takes priority over minimizing muscle activity in the legs. The analysis for Asymmetric Squat, Bend Walk, Bent Over, and Kneeling was divided into three portions: bending down, picking bags, and rising up. Relevant differences between the lift styles for these portions were seen in the biceps femoris, longissimus, and rectus abdominis, with Bend Walk generally being the most taxing activity. Overall, there were minimal differences while rising up from any of these postures with most changes seen in the biceps femoris. Rising Up also generally had a higher peak muscle activity compared to bending down or picking bags.

The final paper in this dissertation evaluates the effect of a different back exoskeleton with the variety of lift styles studied in the second paper. It is important to see how exoskeleton use aids or harms many of the lift styles commonly used by industry workers. Lift side was once again a factor in the Split Legged, Heel Up, and One Legged tasks. Participants benefited more from the exoskeleton in same side lifts as opposed to opposite side. For Asymmetric Squat, Bend Walk, Bent Over, and Kneeling greater benefits were seen in the back and leg muscles while rising up as opposed to bending down. Focusing on the peak of the lift (taken at the peak of bending down for the more static postures) found that the exoskeleton had more significant differences for Split Legged, Heel Up, and One Legged compared to Asymmetric Squat, Bend Walk, Bent Over, and Kneeling. One highly important aspect in evaluating exoskeletons is determining the subject population that would most benefit from its use. Focusing on body mass, the longissimus saw decreased benefits as the body mass increased, with subjects under 75 kg benefiting the most from the exoskeleton, while the iliocostalis and biceps femoris typically saw the opposite effect when results were significant (i.e., heavier subjects benefited the most).