Control of trunk muscles activity while manual material handling symmetrically and asymmetrically, Based on Motor control strategy

[Purpose] Although lifting tasks has been recognized as a primary risk factor in low back pain, the concept of lifting asymmetry is relatively new subject. To address trunk function, biomechanical studies generally measure trunk muscle activity using surface electromyography (EMG). But so far, magnitude and similarity index (SI) obtained from EMG have not been studied as indicators of the motor control during lifting task. So, the purpose of this study is to compare the trunk muscles magnitude and SI during symmetric and asymmetric lifting. [Subjects and Methods] A total of 20 healthy male with no history of lumbar spine disorders participated. Surface electromyography data were recorded from the 7 trunk muscles while the participants performed symmetric and asymmetric lifting and lowering different loads. [Results] According to Multivariate ANOVAs the phase of motion (lifting, lowering) and condition (symmetry, asymmetry) have a significant effect on SI and magnitude (p≤0.05). Load changes have no effect on SI (p=0.969) but have a significant effect on magnitude (p≤0.05). The magnitude and SI value is higher in asymmetrical lifting and lowering compare to symmetrical condition. [Conclusion] The findings reveal the SI value is higher in asymmetric conditions. This means that the amount of muscles co-contracture increased during asymmetrical conditions. Increased muscles co-contracture reinforces the hypothesis of exerting more compression on the spine in asymmetrical movement. Keywords: Asymmetrical lifting, Motor control, Electromyography

Three-dimensional asymmetric maximum weight lifting prediction considering dynamic joint strength

In this study, the three-dimensional (3D) asymmetric maximum weight lifting is predicted using an inverse-dynamics-based optimization method considering dynamic joint torque limits. The dynamic joint torque limits are functions of joint angles and angular velocities, and imposed on the hip, knee, ankle, wrist, elbow, shoulder, and lumbar spine joints. The 3D model has 40 degrees of freedom (DOFs) including 34 physical revolute joints and 6 global joints. A multi-objective optimization (MOO) problem is solved by simultaneously maximizing box weight and minimizing the sum of joint torque squares. A total of 12 male subjects were recruited to conduct maximum weight box lifting using squat-lifting strategy. Finally, the predicted lifting motion, ground reaction forces, and maximum lifting weight are validated with the experimental data. The prediction results agree well with the experimental data and the model’s predictive capability is demonstrated. This is the first study that uses MOO to predict maximum lifting weight and 3D asymmetric lifting motion while considering dynamic joint torque limits. The proposed method has the potential to prevent individuals’ risk of injury for lifting.

Effects of Volitional Spine Stabilization on Trunk Control During Asymmetric Lifting Task in Patients With Recurrent Low Back Pain

Study Design: Prospective, concurrent-cohort study. Objectives: To determine the effects of volitional preemptive abdominal contraction (VPAC) on trunk control during an asymmetric lift in patients with recurrent low back pain (rLBP) and compare with matched controls. Methods: Thirty-two rLBP patients and 37 healthy controls performed asymmetric lifting with and without VPAC. Trunk, pelvis, and hip biomechanical along with neuromuscular activity parameters were obtained using 3-dimensional motion capture and electromyography system. Hypotheses were tested using analysis of variance. Results: The VPAC resulted in significantly reduced muscle activity across all trunk extensor muscles in both groups (M ± SD, 6.4% ± 8.2% of maximum contraction; P ≤ .005), and reduced trunk side flexion (1.4° ± 5.1° smaller; P ≤ .005) and hip abduction (8.1° ± 21.1° smaller; P ≤ .003). rLBP patients exhibited reduced muscle activity in external oblique (12.3% ± 5.5% of maximum contraction; P ≤ .012), as well as decreased hip flexion (4.7°, P ≤ .008) and hip abduction (5.2°, P ≤ .001) at the final position of lifting in comparison with healthy controls. Conclusions: The results of this study defend the recommendation that the use of a VPAC increase spine stability during an asymmetrical loading task. Our results provide an indication that a VPAC strategy that is achieved during an asymmetric lifting decreases exposure for lumbar spine injury and instability. Spine care providers and ergonomists can use this information when designing neuromuscular control training programs, both for healthy individuals aimed at prevention of injury, as well as those with a history of rLBP, aimed at full functional recovery and protection from future injury.

Classification of Lifting Techniques for Application of A Robotic Hip Exoskeleton

The number of exoskeletons providing load-lifting assistance has significantly increased over the last decade. In this field, to take full advantage of active exoskeletons and provide appropriate assistance to users, it is essential to develop control systems that are able to reliably recognize and classify the users’ movement when performing various lifting tasks. To this end, the movement-decoding algorithm should work robustly with different users and recognize different lifting techniques. Currently, there are no studies presenting methods to classify different lifting techniques in real time for applications with lumbar exoskeletons. We designed a real-time two-step algorithm for a portable hip exoskeleton that can detect the onset of the lifting movement and classify the technique used to accomplish the lift, using only the exoskeleton-embedded sensors. To evaluate the performance of the proposed algorithm, 15 healthy male subjects participated in two experimental sessions in which they were asked to perform lifting tasks using four different techniques (namely, squat lifting, stoop lifting, left-asymmetric lifting, and right-asymmetric lifting) while wearing an active hip exoskeleton. Five classes (the four lifting techniques plus the class “no lift”) were defined for the classification model, which is based on a set of rules (first step) and a pattern recognition algorithm (second step). Leave-one-subject-out cross-validation showed a recognition accuracy of 99.34 ± 0.85%, and the onset of the lift movement was detected within the first 121 to 166 ms of movement.

The Effects of Load Stability and Visual Access During Asymmetric Lifting Tasks on Back and Upper Extremity Biomechanical Responses

Objective: To explore the change of muscular and biomechanical responses in different load stability and visual access conditions during an asymmetric lifting task. Background: Previous studies found that lifting unstable loads resulted in changes to the biomechanical loads experienced by the spine and upper extremities. However, researchers have not extensively investigated behaviors when people lift potentially unstable loads. It was hypothesized that lifting a potentially unstable load can lead to changes in lifting behavior, which may be mitigated by visual access to the load. Method: Fourteen volunteers lifted either a stable load or a potentially unstable load that could move within the container during the lifting task. In half of the lifting conditions, the box was covered to restrict visual access when lifting. Spine kinematic and kinetic measures and surface electromyographic (EMG) signals from back, shoulder, and arm muscles were obtained. Results: Lifts of the stable load were faster and generally had higher peak muscle activations than lifts of the potentially unstable load. Participants had less spine flexion when handling the potentially unstable load without visual access. Conclusion: When lifting and moving a potentially unstable load that could lead to a perturbation, people tended to lift the container more slowly comparing with lifting a stable load, which in turn reduced the peak muscle activities. Application: In industry, there are many work situations where workers need to lift or carry unstable loads that can shift during transport. Providing visual access to the load may help mitigate some of these effects.