Maximum acceptable weight of lift reflects peak lumbosacral extension moments in a functional capacity evaluation test using free style, stoop and squat lifting

Machine Learning Model to Estimate Net Joint Moments during Lifting Task Using Wearable Sensors: A Preliminary Study for Design of Exoskeleton Control System

Accurately measuring the lower extremities and L5/S1 moments is important since L5/S1 moments are the principal parameters that measure the risk of musculoskeletal diseases during lifting. In this study, protocol that predicts lower extremities and L5/S1 moments with an insole sensor was proposed to replace the prior methods that have spatial constraints. The protocol is hierarchically composed of a classification model and a regression model to predict joint moments. Additionally, a single LSTM model was developed to compare with proposed protocol. To optimize hyperparameters of the machine learning model and input feature, Bayesian optimization method was adopted. As a result, the proposed protocol showed a relative root mean square error (rRMSE) of 8.06~13.88% while the single LSTM showed 9.30~18.66% rRMSE. This protocol in this research is expected to be a starting point for developing a system for estimating the lower extremity and L5/S1 moment during lifting that can replace the complex prior method and adopted to workplace environments. This novel study has the potential to precisely design a feedback iterative control system of an exoskeleton for the appropriate generation of an actuator torque.

Understanding individual differences in lifting mechanics: Do some people adopt motor control strategies that minimize biomechanical exposure

The movement strategy an individual uses to complete a lift can influence the resultant biomechanical exposure on their low back. We hypothesize that some lifters may choose a motor control strategy to minimize exposure to the low back, where others may not. Lower magnitudes of exposure to the low back coupled with less variability in lift-to-lift exposure and in features of movement strategy related to biomechanical exposure would support that such lifters consider minimizing exposure in their motor control strategy. We tested this hypothesis by investigating if differences in variability of low back exposure measures, as well as features of movement strategy related to resultant low back exposures differed across lifters. Twenty-eight healthy adults participated in the study where ten repetitions of a lifting task with the load scaled to 75% of participant's one-repetition maximum were completed. In all trials, whole-body kinematics and ground reaction forces were collected. Lifters were grouped as low, moderate or high relative exposure based on low back flexion angles and normalized L4/L5 extensor moments when lifting. Principal component analysis was used to identify independent movement strategy features, and statistical testing determined which features differed between high and low exposure lifts. Variability in low back exposures and movement features associated with relative biomechanical exposure were compared across lifter classifications. Significantly less variability was observed in low back exposures among the low exposure lifter group. Additionally, a trend towards lower variability in movement features associated with relative biomechanical exposure was also observed in low exposure lifters. These findings provide initial support for the hypothesis that some lifters likely define a motor control strategy that considers minimizing biomechanical exposure in addition to completing the lift demands. Future work should explore how state and trait-based factors influence an individual to consider biomechanical exposure within their motor control strategy in lifting.

Are psychophysically chosen lifting loads based on joint kinetics?

Tables of maximal acceptable weight limits (MAWL) are used to select safe lifting loads and help reduce workplace injuries. However, their subjective basis provides little information on the underlying load selection rationale, and few studies have examined MAWLs in relation to full-body joint demands. Therefore, link-segment biomechanical modeling was applied for 18 participants during three sagittal 4.3 lifts/minute tasks at chosen MAWL levels. Each lift produced unique kinematics, kinetics, MAWL loads and most highly stressed joints. Lifting from the lowest starting position most heavily challenged the L5/S1 joint, whereas more upright starting postures stressed the shoulder. Lifting loads above and below MAWL level demonstrated consistent joint loading patterns. The normalized peak moments of the highest stressed joint were similar across the lifts at ∼70-75% of the joint maximum. Our results suggest that MAWLs may be chosen based on perception of the most stressed joint for the specific lift.

Neck posture during lifting and its effect on trunk muscle activation and lumbar spine posture

Neck and head posture have been found to have a significant influence on the posture of the lower spine region during lifting and both an extended/upward gaze and a flexed/downward gaze have been hypothesized to lead to increased pain and/or overuse of the neck musculature. As a result, strength training recommendations have turned to the use of a retracted neck posture as being the safer posture to assume during lifting. This study examined trunk and neck muscle activity and lumbar spine posture in seven participants while performing moderate load lifts using a retracted neck posture (chin drawn in posteriorly; recently gaining popularity among coaches, trainers, and physical therapists to reduce neck pain during lifting, and freestyle neck posture (no instructions given). The retracted neck resulted in less lumbar spine flexion and increased lumbar erector spinae, external oblique, and sternocleidomastoid activity. The retracted posture also resulted in decreased activity in the thoracic erector spinae and dorsal neck musculature. The increased trunk and sternocleidomastoid activity and decreased spine flexion observed in the seven participants of this study when lifting with a retracted neck may have the potential to help lower the risk of spine pain/injury.

The Correlation between the Muscle Activity and Joint Angle of the Lower Extremity According to the Changes in Stance Width during a Lifting Task

[Purpose] This study examined the correlation between the muscle activities and joint angle of the hip and knee according to the changes in stance width during a lifting task. [Subjects and Methods] The subjects of this study were 15 healthy students. A three-dimensional motion analyzer (SMART-E, BTS, Italy) was used to measure the joint angles of hip and knee during lifting. An 8-channel electromyograph (8-EMG) (Pocket EMG, BTS, Italy) was used to measure muscle activities of the erector spinae, gluteus maximus, rectus femoris, and tibialis anterior during lifting. The collected data were analyzed using the Pearson-test and SPSS 18.0. [Result] The muscle activity of the tibialis anterior was significantly decreased by increasing the stance width (r= -0.285). Muscle activity of the erector spinae was significantly decreased by increasing the knee angle (r= -0.444). The muscle activity of the gluteus maximus was significantly increased by increasing the muscle activity of the tibialis anterior (r= 0.295). [Conclusion] Efficient lifting is possible when stance width and knee flexion are increased, which results in reduced muscle activity of the tibialis anterior and the erector spinae. Lifting is facilitated when the muscle activities of the gluteus maximus and tibialis anterior are correlated.