The Influence of External Load Configuration on Trunk Musculature and Spinal Stability during Manual Material Handling

The performance of manual material handling (MMH) tasks is highly associated with lower back injuries due to the excessive acute and/or cumulative mechanical loading that spinal tissues experience. Therefore, it is critical to understand how different characteristics of MMH tasks could become potential risk factors that change back injury risks and to develop proper MMH strategies that could reduce their biomechanical impacts to the spine. In this study, we explored the effects of external load configuration on trunk musculature and spinal stability during static loading and sudden loading scenarios.;The main objective of the current research was to explore how the configuration of an external weight (e.g. weight distribution or arrangement of the parts of the weight) can influence trunk biomechanics and spinal stability during the performance of static loading and sudden loading. To this end, we have conducted two experiments each of which was designed to simulate the two scenarios mentioned above.;In the first experiment, we investigated the influence of the weight configuration of hand loads on trunk muscle activities and the associated spinal stability during static weight holding. Thirteen volunteers each performed static weight holding tasks using two different 9 kg weight bars (with medial and lateral weight configurations) at two levels of height (low and high) and one fixed horizontal distance (result in constant spinal joint moment across conditions). Results of this study demonstrated that holding the laterally distributed load significantly reduced activation levels of lumbar and abdominal muscles by 9 to 13% as compared with holding the medially distributed load.;In the second study, we examined the effects of different configurations of hand load on spine biomechanics and trunk stability during sudden loading events. Fifteen asymptomatic volunteers experienced sudden loadings using the same magnitude of weight (9 kg) with two different configurations (medially or laterally distributed) at three levels of height (low, middle, and high) and one fixed horizontal distance (constant spinal joint moment across conditions). Results of this study revealed that holding the medially distributed weight resulted in a significantly higher effective trunk stiffness (on average, lateral: 1785 Nm/rad and medial: 2413 Nm/rad) and peak L5/S1 joint compression force (on average, lateral: 2694 N and medial: 2861 N) compared with the laterally distributed weight.;We believe such effects are due to an elevated rotational moment of inertia when the weight of the load is laterally distributed. These findings suggest that during the design and assessment of manual material handling tasks such as lifting and carrying, the weight configuration of the hand load should be considered. According to the results, it was concluded that when confronted with static and sudden loading incidents, the load with larger moment of inertia (i.e. laterally distributed load) could help reduce the risk of low back injury compared to the load with a smaller moment of inertia (i.e. medially distributed load)

Effects of fatigue on trunk stability in elite gymnasts

The aim of the present study was to test the hypothesis that fatigue due to exercises performed in training leads to a decrement of trunk stability in elite, female gymnasts. Nine female gymnasts participated in the study. To fatigue trunk muscles, four series of five dump handstands on the uneven bar were performed. Before and after the fatigue protocol, participants performed three trials of a balancing task while sitting on a seat fixed over a hemisphere to create an unstable surface. A force plate tracked the location of the center of pressure (CoP). In addition, nine trials were performed in which the seat was backward inclined over a set angle and suddenly released after which the subject had to regain balance. Sway amplitude and frequency in unperturbed sitting were determined from the CoP time series and averaged over trials. The maximum displacement and rate of recovery of the CoP location after the sudden release were determined and averaged over trials. After the fatigue protocol, sway amplitude in the fore-aft direction was significantly increased (p = 0.03), while sway frequency was decreased (p = 0.005). In addition, the maximum displacement after the sudden release was increased (p = 0.009), while the rate of recovery after the perturbation was decreased (p = 0.05). Fatigue induced by series of exercises representing a realistic training load caused a measurable decrement in dynamic stability of the trunk in elite gymnasts

Trunk Biomechanical Responses during Sudden Loading

Back injury caused by sudden loading is a significant risk among workers who perform manual material handling tasks (MMH). Therefore, it is critical to understand the effects of influential factors on back injury risks during sudden loading, and to develop load handling strategies that can reduce the biomechanical impacts to the spine caused by sudden loading. In this study we explored the effects of foot placement, load handling position as well as uneven ground conditions on trunk biomechanical responses under sudden loading event.;In the first experiment we investigated the effects of different foot placements and load asymmetry on trunk biomechanics during sudden loading. Fifteen subjects experienced sudden release of a 6.8 kg external load from symmetric or asymmetric directions while maintaining four different foot placements. The results showed that subjects experienced on average 4.1 degrees less trunk flexion, 6.6 Nm less L5/S1 joint moment and 32.0 N less shear force when using staggered stance with right foot forward (the most preferred placement) in comparison to wide stance (the least preferred placement). Asymmetric load releasing position consistently resulted in smaller trunk biomechanical impact than symmetric position. The findings suggest that staggered stance and asymmetric load holding position can be used as a protective load handling posture against low back pain caused by sudden loading.;In the second experiment we investigated the effects of load handling position on trunk biomechanics during sudden loading. Eleven male subjects were exposed to a 6.8 kg sudden loading while standing upright and holding the load at three different vertical heights in the sagittal plane or 45 degree asymmetric to the sagittal plane. Results showed that subjects experienced smaller spinal compression with the decrease of load holding height; more specifically, at the \u27Low (umbilicus level)\u27 height condition, the peak L5/S1 joint compression force was 10.1% and 15.1% less than the \u27Middle (shoulder level)\u27 and \u27High (eyebrow level)\u27 conditions, respectively. Further, asymmetric posture resulted in 3.9% less compression force than symmetric posture. These findings suggest that handling loads in a lower position could work as a protective strategy when experiencing sudden loading.;In the third experiment we investigated the effects of uneven ground conditions on trunk biomechanical responses during sudden loading. Thirteen subjects experienced sudden loading with two different weights (3.4 kg and 6.8 kg) while standing on flat or laterally slanted ground conditions (0°, 15° and 30°). Our results showed that subjects experienced larger peak L5/S1 joint compression force with the increase of ground slanted angle. On average, the peak L5/S1 joint compression force generated in the 30° condition was 6% and 8% larger than 15° and 0° conditions, respectively. Furthermore, greater trunk biomechanical impact was constantly observed in the 3.4 kg weight condition compared with the 6.8 kg condition. Findings of this study suggest that standing on laterally slanted ground surface increases the risk of low back injury when experiencing sudden loading

THE STUDY OF TRUNK MECHANICAL AND NEUROMUSCULAR BEHAVIORS

Low back pain (LBP) is a common ailment in the United States, affecting up to 80% of adults at least once in their lifetime. Although 90% of LBP cases are considered nonspecific, recent studies show that abnormal mechanics of the lower back can be a major factor. One method of assessing the lower back mechanical environment is through perturbation experiments. An intensive literature review of perturbation systems was used to select and develop a system for the Human Musculoskeletal Biomechanics Lab (HMBL). Following construction, individuals with high/low exposure to day-long physical activity were assessed to quantify daily changes in their lower back mechanics and determine whether complete recovery occurs during overnight rest. Despite significant decrease in maximum voluntary contractions (MVC), intrinsic stiffness of the high exposure group remained constant following day-long physical activity. The final component of this Master’s project is devoted to the design of a wobble chair system for study of trunk stability. Development of the perturbation system and wobble chair are hoped to facilitate future research aimed at a better understanding of trunk mechanical and neuromuscular behaviors to prevent and treat LBP in the future

NEUROMUSCULAR RESPONSE OF THE TRUNK FOLLOWING INERTIAL-BASED PERTURBATIONS WITH WHOLE-BODY VIBRATION EXPOSURE

The purpose of this study was to evaluate the effects of vibration exposure on the neuromuscular responses to inertial-based trunk perturbations. Thirteen, male participants (mean = 22.5 yrs ± 3.2) were assigned to one of two experimental groups: 1) participants not exposed to vibration (control group - CG, n=6), and, 2) participants exposed to vibration (vibration group - VG, n=7) throughout the protocol. Participants experienced 40 perurbations, of which half were in known and unknown directions. Data from trunk sEMG, motion capture markers and seat accelerometers were anaylzed. Repeated measures ANOVA with Tukey\u27s post hoc test were used to determine statistical significance (p\u3c0.05). Participants in CG had a 14% faster muscle onset time than VG. Antagonistic muscle onset times were faster than agonists in both groups. Perturbations of known direction did not show any anticipation effects both in sEMG amplitude and in L4-5 joint angle

The Effect of Whole Body Horizontal Vibration in Position Sense and Dynamic Stability of the Spine

In many workplaces, workers are exposed to whole body vibration which involves multi-axis motion in fore-aft (x axis), lateral (y axis) and vertical (z axis) directions. In previous studies, our laboratory has found changes in biomechanical responses such as response time and position sense with exposure to vibration in single vertical direction. The objective of the current study was to investigate the effect of whole body, horizontal vibration on proprioception and sudden loading dynamics and to compare these results with the previously studied whole body vertical vibration experiment. Both position sense test and sudden loading test were performed in three conditions: a pre-exposure condition (pre), a post-washout condition (postw) and a post-vibration condition (postv). Subjects were exposed to the whole body horizontal vibration frequency of 5 Hz and constant acceleration of 0.284 RMS (m/s-2) for 30 minutes. Absolute reposition sense error increased slightly after vibration exposure (relative to after quiet sitting (postw)), although the results were not significant. Times to peak muscle response and flexion magnitude were also increased after horizontal vibration exposure, suggesting a decreased stability of the spine, but again these results were not significant. Compared to the previous study of vertical whole body vibration, the effects of horizontal vibration in this study were small and not significant. This may be due to differences in the transmissibility of vertical and horizontal vibrations at the 5 Hz frequency. These results would suggest that horizontal vibration may be less of a factor in whole-body vibration induced injuries. This work was supported by University of Kansas Transportation Research Institute Grant Program

Biomechanics

Biomechanics is a vast discipline within the field of Biomedical Engineering. It explores the underlying mechanics of how biological and physiological systems move. It encompasses important clinical applications to address questions related to medicine using engineering mechanics principles. Biomechanics includes interdisciplinary concepts from engineers, physicians, therapists, biologists, physicists, and mathematicians. Through their collaborative efforts, biomechanics research is ever changing and expanding, explaining new mechanisms and principles for dynamic human systems. Biomechanics is used to describe how the human body moves, walks, and breathes, in addition to how it responds to injury and rehabilitation. Advanced biomechanical modeling methods, such as inverse dynamics, finite element analysis, and musculoskeletal modeling are used to simulate and investigate human situations in regard to movement and injury. Biomechanical technologies are progressing to answer contemporary medical questions. The future of biomechanics is dependent on interdisciplinary research efforts and the education of tomorrow’s scientists

Integrative Spine Dynamics with respect to Pushing, Pulling and Lifting

The purpose of this project is to understand spine dynamics with respect to the manufacturing activities of pushing, pulling and carrying. Extensive background research was conducted to obtain information about spine physiology, dynamics and stability. Stability indices were created with data from Yale University. An inverted pendulum is used as a spine model, with springs and dampers representing flexors and extensors. This model is used to determine if the spine is dynamically stable when experiencing forces from the three activities

Motor control in people with low back pain : the effects of pain, exercise, and a simulated round of golf

Low back pain is considered a multifactorial condition, with biological and psychosocial features contributing to symptoms. Contemporary theories on motor adaptations to pain implicate altered motor control as a biological feature that contributes to the onset, recurrence, and persistence of low back pain. Unsurprisingly, ameliorating altered motor control is a target for some therapeutic interventions for people with low back pain. However, whether motor control is consistently altered in the presence of low back pain is unclear. In addition, motor control improvements following exercise in people with low back pain are conflicting when examined using muscle onsets, yet few studies have examined changes in other motor control measures. Finally, despite contemporary theories suggesting altered motor control contributes to symptom recurrence, there is currently a paucity of evidence observing altered motor control leading to symptom exacerbation during ecologically valid tasks. To address these gaps in the literature, a series of studies were conducted. This thesis therefore investigated: (1) is motor control consistently altered in the presence of low back pain based on measures of anticipatory and compensatory postural adjustments? (2) Do commonly prescribed exercise interventions improve motor control in people with low back pain based on anticipatory and compensatory postural adjustments? And (3) do golfers with low back pain exhibit altered motor control during the golf downswing and are these alterations accompanied by an exacerbation of low back pain? The findings of this thesis improve our understanding of the role of motor control alterations in people with LBP. This thesis provides support for contemporary theoretical models of altered motor control in people with LBP, suggesting altered motor control is a feature of LBP. This thesis provides support for exercise interventions that aim to improve trunk motor control in people with LBP. An interesting finding was the reduction in EO activity which was accompanied by increased trunk deviation phase and X-factor variables — recorded during the golf swing — over the course of a simulated round of golf in golfers with LBP. This finding suggests the adoption of a “loose” motor control strategy. However, the adoption of a “loose” motor control strategy was not accompanied by subsequent pain provocation, which challenges the proposed causal relationship between altered motor control and pain