The effect of stance width on trunk kinematics and trunk kinetics during sagitally symmetric lifting

Lifting technique can have a significant impact on spine loading during lifting. The sports biomechanics literature has documented changes in trunk and lower extremity kinematics and muscle coactivation patterns as a function of stance width during high force dead lift and squat exercises. The focus of the current study was to explore whether these lifting stance width effects might translate into the occupational setting under more moderate load level conditions. Twelve subjects performed repetitions of a sagittally symmetric lifting and lowering task (10 kg load) under three stance width conditions: narrow (feet together), moderate (feet shoulder width) and wide (feet 150% of shoulder width). As they performed these exertions, trunk kinematics were captured using the lumbar motion monitor while the activity of the trunk muscles (erector spinae, rectus abdominis) and lower extremity muscles (gluteus maximus, vastus lateralis and vastus medialis) were evaluated using normalized electromyography. The results showed that both the range of motion and peak acceleration in the sagittal plane were significantly affected by the stance width. The muscle activation levels, however, were not significantly affected by the stance width. These results collectively would indicate that the stance width effects seen in power lifting activities do not translate well into the occupational environment where more moderate loads are typically lifted.

Relevance to industry

Exploring alternative lifting strategies may provide an opportunity to reduce the incidence of low back disorders. Lifting stance width is one variable that has not been explored in the ergonomics literature.     

Kinematics of the trunk in sitting posture: An analysis based on the instantaneous axis of rotation

This paper presents a new approach for analysing trunk kinematics in sitting posture based on the characterisation of thorax and pelvis motion by means of ranges of motion and instantaneous axes of rotation (IAR). These variables are estimated from videophotogrammetric data. An experiment was carried out in order to analyse three motions associated with the flexion–extension movement: the absolute motions of the pelvis and thorax and the relative motion between the thorax and pelvis. The results obtained suggest a sequential activation of lumbar vertebrae in the flexion–extension motion. On the other hand, the location of the pelvis IAR shows that the movement of the pelvis on the seat is not just a rolling motion but a rolling with some level of sliding. Finally, the location of the IAR in the thorax-pelvis relative motion shows a mismatch between the trunk IAR and the backrest axis of rotation in several office chairs. The proposed technique provides a new approach for the kinematic analysis of sitting posture. The results can be applied to the improvement of biomechanical models of seated posture as well as to define some design criteria of work seats based on the fit between the trunk and backrest movements.     

Effects of load and speed on lumbar vertebral kinematics during lifting motions

This experimental study investigated the effects of load magnitude and movement speed on lumbar vertebral kinematics during lifting task performance. Ten participants performed sagittally symmetric lifting movements with systematically varied load using either a normal or a faster-than-normal speed. Skin-surface markers were strategically placed over the participants' spinous processes and other landmarks representing major body joints and were recorded during the movements by a motion capture system. The center of rotation (COR) locations and segmental movement profiles for lumbar vertebrae L2 to L5 were derived and analyzed. Results suggested that (a) the COR locations and vertebral angular displacement were not significantly affected by the speed or load variation; (b) a faster speed tended to shorten the time to complete the acceleration for all the lumbar vertebrae considered; and (c) the load increase incurred a tendency for the L5 to complete the primary displacement in a briefer time while enduring greater peak acceleration and velocity. The findings lead to a better understanding of the relation between lifting dynamics and spinal motion. Potential applications of this research include the development of more accurate biomechanical models and software tools for depicting spinal motions and quantifying low-back stress.     

The interrelationship of the thorax and pelvis under varying task constraints

The purpose of this study was to investigate the interrelationship between the thorax and pelvis during coupled movement patterns. Fifty-seven participants were assessed using an infrared motion analysis system to track trunk movement during maximal pelvis and thorax rotations over four trunk inclinations and two pelvic constraint conditions. A repeated-measures multivariate analysis of variance investigated the effects of forward trunk inclination and pelvic constraint on thorax and pelvic rotation. Forward trunk inclination from neutral to 45° resulted in a 46% (p < 0.001) decrease in axial pelvic rotation and a 15% (p < 0.001) decrease in axial thorax rotation with an unconstrained pelvis. A constrained pelvis resulted in a 15% (p < 0.001) decrease in axial thorax rotation. An externally constrained pelvis allowed the thorax to achieve an average of 18° (SD = 2°) greater rotational range of motion across all angles. This study reinforced the importance of allowing the pelvis to rotate during whole body axial rotation tasks.

Practitioner Summary: Results indicated that maximum axial trunk rotation is best achieved in a neutral posture, when the pelvis is allowed to contribute and flexion at the hips should be minimised. For example, if a recumbent task requires rotation of the torso, then the chair seat should be allowed to swivel.     

Comparison of two heights for forward-placed trunk support with standing work

Two forward-placed supports with different heights are investigated using human motion capture and EMG. Ten male participants stood in 10° increments of trunk flexion between 0 and 40° for three conditions; leaning on a desk adjusted to the height of the pelvis, leaning on a prototype support at the height of the sternum and with no external support. Low back and hip extensor muscle activity was reduced by an average 60% with leaning against the prototype compared to the no-support condition whereas leaning on a desk produced no significant change in muscle activity. Supported conditions resulted in greater forward displacement of the trunk by at least two-fold compared to no-support representing a longer reach distance. No adverse changes in kinematics indicate that either support blocked segmental flexion of the pelvis, lumbar spine or thoracic spine. These findings suggest that leaning against a higher-placed trunk support could be beneficial for tasks requiring forward flexion.     

The effect of sinusoidal rolling ground motion on lifting biomechanics

The objective of this study was to quantify the effects of ground surface motion on the biomechanical responses of a person performing a lifting task. A boat motion simulator (BMS) was built to provide a sinusoidal ground motion (simultaneous vertical linear translation and a roll angular displacement) that simulates the deck motion on a small fishing boat. Sixteen participants performed lifting, lowering and static holding tasks under conditions of two levels of mass (5 and 10 kg) and five ground moving conditions. Each ground moving condition was specified by its ground angular displacement and instantaneous vertical acceleration: A): +6°, −0.54 m/s²; B): +3°, −0.27 m/s²; C): 0°, 0 m/s²; D): −3°, 0.27 m/s²; and E): −6°, 0.54 m/s². As they performed these tasks, trunk kinematics were captured using the lumbar motion monitor and trunk muscle activities were evaluated through surface electromyography. The results showed that peak sagittal plane angular acceleration was significantly higher in Condition A than in Conditions C, D and E (698°/s² vs. 612–617°/s²) while peak sagittal plane angular deceleration during lowering was significantly higher in moving conditions (conditions A and E) than in the stationary condition C (538–542°/s² vs. 487°/s²). The EMG results indicate that the boat motions tend to amplify the effects of the slant of the lifting surface and the external oblique musculature plays an important role in stabilizing the torso during these dynamic lifting tasks.     

Hand-hold location and trunk kinematics during box handling

Trunk kinematics variables have been shown to be related to low back injury risk during lifting tasks and it was hypothesised that changes in hand-hold positions could influence trunk kinematics and thereby risk. Fourteen subjects lifted a 5 or 10 kg box using four different hand placement locations (two symmetric and two asymmetric) while their trunk kinematics (position, velocity and acceleration in the sagittal, coronal and transverse planes) were captured using the lumbar motion monitor (LMM). These kinematics data were then used to calculate the probability of high risk group membership (PHRGM) as defined in the LMM risk assessment model. The results showed significant effects of hand placement on trunk kinematics, resulting in significant changes in the PHRGM variable ranging from a low of 20% in a the symmetric low load condition to a high of 38% under the asymmetric, 10 kg condition.

Statement of Relevance: Manual materials handlers use a variety of hand-hold positions on boxes during lifting. Where a lifter grabs the box can influence the trunk kinematics during the lifting task and these kinematics have been shown to provide some insight into risk of low back injury. This study documents the trunk postures and kinematics as a function of hand-hold position.     

The effect of sinusoidal rolling ground motion on lifting biomechanics

The objective of this study was to quantify the effects of ground surface motion on the biomechanical responses of a person performing a lifting task. A boat motion simulator (BMS) was built to provide a sinusoidal ground motion (simultaneous vertical linear translation and a roll angular displacement) that simulates the deck motion on a small fishing boat. Sixteen participants performed lifting, lowering and static holding tasks under conditions of two levels of mass (5 and 10 kg) and five ground moving conditions. Each ground moving condition was specified by its ground angular displacement and instantaneous vertical acceleration: A): +6°, −0.54 m/s²; B): +3°, −0.27 m/s²; C): 0°, 0 m/s²; D): −3°, 0.27 m/s²; and E): −6°, 0.54 m/s². As they performed these tasks, trunk kinematics were captured using the lumbar motion monitor and trunk muscle activities were evaluated through surface electromyography. The results showed that peak sagittal plane angular acceleration was significantly higher in Condition A than in Conditions C, D and E (698°/s² vs. 612-617°/s²) while peak sagittal plane angular deceleration during lowering was significantly higher in moving conditions (conditions A and E) than in the stationary condition C (538-542°/s² vs. 487°/s²). The EMG results indicate that the boat motions tend to amplify the effects of the slant of the lifting surface and the external oblique musculature plays an important role in stabilizing the torso during these dynamic lifting tasks.     

Injury-induced kinematic compensations within the lower back: impact of non-lower back injuries

With the number of musculoskeletal disorders increasing in the workplace, the potential exists for multiple injuries due to compensations. The objective of this study was to quantify the impact of non-lower back injuries on the trunk motions adopted by the individual during typical lifting tasks. A total of 32 injured subjects (eight for each injury group--shoulder, hand/wrist, knee and foot/ankle) and 32 matched (gender, height and weight) healthy subjects performed laboratory lifting tasks. The independent variables were task asymmetry (clockwise, sagittally symmetric and counter-clockwise), lift origin (waist, knee and floor) and box weight (2.27 and 6.82 kg). The dependent variables were peak trunk kinematics (as measured by the lumbar motion monitor) and moment arm between the box and lower back. The two injuries that had the greatest impact on the lower back kinematics were foot/ankle and hand/wrist. Individuals who suffered a foot/ankle injury produced greater three-dimensional trunk velocities (up to 10 degrees/s) while individuals with hand/wrist injuries slowed down in the sagittal plane but increased the twisting velocity--specifically when lifting from the asymmetric shelves. Knee and shoulder injuries had limited impact on the trunk motions. Overall, the results indicate workplace design must take into account non-lower back injuries.     

Lumbar motion response to a constant load velocity lift

An experiment was performed to evaluate the motions of the lumbar spine during a constant load velocity lift. For the purposes of this study, a constant load velocity refers to the linear vertical velocity of the load. This vertical load velocity was controlled using a modified angular isokinetic dynamometer, which produced linear isokinetic motion during a lift. A lumbar monitor was used to observe the position, velocity, and acceleration changes that occurred in the lumbar spine during the lifting task. The results indicate that under constant load velocity conditions, significant angular accelerations occur at the lumbar level. The nature of these accelerations was found to depend on several variables associated with a lifting task, such as the load velocity and the asymmetry of the lift. The physical significance of these results would be increased spinal loading above that which would be predicted using a static model.     

Injury-induced kinematic compensations within the lower back: impact of non-lower back injuries

With the number of musculoskeletal disorders increasing in the workplace, the potential exists for multiple injuries due to compensations. The objective of this study was to quantify the impact of non-lower back injuries on the trunk motions adopted by the individual during typical lifting tasks. A total of 32 injured subjects (eight for each injury group—shoulder, hand/wrist, knee and foot/ankle) and 32 matched (gender, height and weight) healthy subjects performed laboratory lifting tasks. The independent variables were task asymmetry (clockwise, sagittally symmetric and counter-clockwise), lift origin (waist, knee and floor) and box weight (2.27 and 6.82 kg). The dependent variables were peak trunk kinematics (as measured by the lumbar motion monitor) and moment arm between the box and lower back. The two injuries that had the greatest impact on the lower back kinematics were foot/ankle and hand/wrist. Individuals who suffered a foot/ankle injury produced greater three-dimensional trunk velocities (up to 10°/s) while individuals with hand/wrist injuries slowed down in the sagittal plane but increased the twisting velocity—specifically when lifting from the asymmetric shelves. Knee and shoulder injuries had limited impact on the trunk motions. Overall, the results indicate workplace design must take into account non-lower back injuries.     

The changes of lumbar muscle flexion–relaxation response due to laterally slanted ground surfaces

Lifting tasks performed on uneven ground surfaces are common in outdoor industries. Previous studies have demonstrated that lifting tasks performed on laterally slanted ground surfaces influence lumbar muscle activation and trunk kinematics. In this study, the effect of laterally slanted ground surfaces on the lumbar muscle flexion–relaxation responses was investigated. Fourteen participants performed sagittal plane, trunk flexion–extension tasks on three laterally slanted ground surfaces (0° (flat ground), 15° and 30°), while lumbar muscle activities and trunk kinematics were recorded. Results showed that flexion–relaxation occurred up to 6.2° earlier among ipsilateral lumbar muscles with an increase in laterally slanted ground angle; however, the contralateral side was not affected as much. Our findings suggest that uneven ground alters the lumbar tissue load-sharing mechanism and creates unbalanced lumbar muscle activity, which may increase the risk of low back pain with repeated exposure to lifting on variable surfaces.

Practitioner Summary: Uneven ground surfaces are ubiquitous in agriculture, construction, fishing and other outdoor industries. A better understanding of the effects of laterally slanted ground surfaces on the interaction between passive and active lumbar tissues during lifting tasks could provide valuable knowledge in the design of preventive strategies for low back injuries.     

The effects of load weight and load starting height on variability of lifting kinematics and kinetics

Trunk kinematic variables have been used to understand the risk of low back injuries in the workplace. Variability in the trunk kinematics as an individual performs a repetitive lifting task is an underexplored area of research. In the current study, it was hypothesized that workplace variables (starting height of lift and load weight) would have an impact on the variance in the kinematic and kinetic variables. Twenty participants performed 60 repetitions of an asymmetric lifting task under four different conditions representing two levels of load weight (5% or 10% of the participant's body weight) and two levels of starting height (80% or 120% of the participant's knee height). The Lumbar Motion Monitor was used to capture trunk kinematic variables from the concentric range of lifting motion while ground reaction forces were collected using a force platform. The primary dependent variables were the variance of kinematic and kinetic variables across these 60 repetitions. The results showed a significant effect of starting height on the variance of sagittal plane trunk kinematics with the lower starting height generating an increased variance (sagittal range of motion increased by 55%, average sagittal velocity increased by 95%, peak sagittal velocity increased by 105%, and peak sagittal acceleration increased by 130%). There was no consistent significant main effect of either independent variable on the variance of the transverse plane kinematics. Additionally, there was no significant effect of load weight on the variance of any trunk kinematic variables tested. In terms of ground reaction forces, it was shown that the starting height of the load had a significant effect on the variance of peak vertical ground reaction force, while the weight of the load had a significant effect on the variance of the peak shear force.     

A Review of: “Human Error in Medicine”, edited by MARILYN SUE BOGNER,Lawrence Erlbaum,Hillsdale (1994), pp. xv + 411, 536-00 (pbk). ISBN 0-8058-1386-1; $79·95 (hbk), ISBN 0-8058-1385-3.

This work investigated maximal voluntary lateral hand pulling force in 18 healthy, habitually active men. Measurements were made in standing at different static angles of lateral trunk flexion, as well as at different constant lifting and lowering velocities. Movement was constrained to the frontal plane, velocity was controlled by an isokinetic dynamometer, pulling force was measured with a strain gauge and overall lateral angular displacement of the trunk by an electrogoniometer. Mean peak pulling force values ranged from 478 to 658 N (static), 291 to 528 N (lifting), and 801 to 911 N (lowering), respectively. The static pulling forces were the highest in flexed positions to the loaded side (10 and 20 trunk angles). In lifting, peak and position-specific pulling force decreased with increasing velocity. Peak lifting force occurred in a flexed trunk position of 7 to 9 to the loaded side. In lowering, pulling forces were significantly higher than during lifting at corresponding velocities and showed less changes with velocity. Peak lowering force occurred at a trunk angle of- 7 to- 11, that is towards the unloaded side. In conclusion, maximal voluntary pulling force in the frontal plane was found to be task dependent. Lowering was accompanied by higher forces and a different velocity and position dependency than lifting which, in addition to the fact that the trunk muscles act predominantly eccentrically during the lowering task, may impose an increased risk of injury.     

Trunk kinematics of one-handed lifting,and the effects of asymmetry and load weight

Abstract

This study investigated trunk kinematic differences between lifts performed using either one hand (unsupported) or two hands. These effects were studied while beginning the lifts from different asymmetric starting positions and while lifting different load weights. Each subject lifted a box from a lower to an upper platform under one- and two-handed lifting conditions. Subjects wore a lumbar spine electrogoniometer, from which relative motion components were calculated in the trunk's three cardinal planes. Results of this study showed that one-handed lifting resulted in significantly higher ranges of motion in the lateral and transverse planes and greater flexion in the sagittal plane. Back motion characteristics previously found to be associated with low back disorders were all significantly higher for one-handed lifts. The two-handed lift technique, on the other hand, produced overall faster trunk motions in the sagittal plane and equal or larger acceleration and deceleration magnitudes in all planes of motion. Increases in load asymmetry affected trunk kinematics, in that magnitude values for range of motion, velocity and acceleration became much greater with increasingly asymmetric load positions. Increasing the load weight appeared to have less of an effect on trunk kinematics, with increases in position mostly occurring during sagittal and lateral bending. These results suggest that unsupported one-handed lifting loads the spine more than two-handed lifts, due to the added coupling. Applying these results to a previously developed model, one-handed lifting was also found to increase one's risk of suffering a low back disorder.     

Changes in trunk muscle activation and lumbar-pelvic position associated with abdominal hollowing and reach during a simulated manual material handling task

The purpose of this study was to investigate the effect of abdominal hollowing (AH) on trunk muscle activation and lumbar-pelvic motion during a controlled lift and replace task. Surface electromyograms were recorded from five abdominal and two back muscle sites. Sagittal lumbar-pelvic motion was recorded by video. Subjects lifted a 3.8 kg load in normal, maximum and extreme reaches, first while performing their preferred lifting style (PLS) and then maintaining an AH technique. The external oblique muscle site activities were significantly higher (p < 0.05) for the AH technique (ranging from 7–20% of maximal voluntary activation (MVIC)) than at any of the abdominal sites for the PLS (ranging from 2–10% MVIC). Differences were found among abdominal sites for the AH, but not for the PLS. The back muscle site activities (ranging from 9–30% MVIC) were significantly higher (p < 0.05) than for any of the abdominal muscles for all conditions, except for the anterior external oblique for AH. The pelvic and lumbar angles changed significantly (p < 0.05) between normal and maximal reaches and between techniques. The AH technique altered abdominal muscle activation amplitudes, with minimal differences in trunk extensors compared to the PLS. The AH resulted in more posterior pelvic tilt.     

Evaluation of the effect of backpack load and position during standing and walking using biomechanical,physiological and subjective measures

Recommendations on backpack loading advice restricting the load to 10% of body weight and carrying the load high on the spine. The effects of increasing load (0%–5%–10%–15% of body weight) and changing the placement of the load on the spine, thoracic vs. lumbar placement, during standing and gait were analysed in 20 college-aged students by studying physiological, biomechanical and subjective data. Significant changes were: (1) increased thorax flexion; (2) reduced activity of M. erector spinae vs. increased activation of abdominals; (3) increased heart rate and Borg scores for the heaviest loads. A trend towards increased spinal flexion, reduced pelvic anteversion and rectus abdominis muscle activity was observed for the lumbar placement. The subjective scores indicate a preference for the lumbar placement. These findings suggest that carrying loads of 10% of body weight and above should be avoided, since these loads induce significant changes in electromyography, kinematics and subjective scores. Conclusions on the benefits of the thoracic placement for backpack loads could not be drawn based on the parameter set studied.     

Impact of order and load knowledge on trunk kinematics during repeated lifting tasks

OBJECTIVE: To determine if lifting random unknown weights is more detrimental than lifting sequences of unknown weights and to investigate whether load knowledge impacts the effect of lifting random box weights. BACKGROUND: Much research has investigated lifting under known load conditions, but few studies have investigated unknown loads, especially when presented in random order. There has been some documentation of alteration in trunk mechanics when there is an overestimation of the unknown load. METHOD: Ten men and 10 women performed three lifting tasks: random unknown, random known, and same weight. A lumbar motion monitor was used to collect kinematic data, and Borg's Rating of Perceived Exertion (RPE) and a task risk rating were also assessed. RESULTS: Both presentation order and load knowledge impacted trunk kinematics during repeated lifting tasks. However, these differences were relatively low in magnitude. Furthermore, kinematic response and perceived risk and exertion for these conditions varied between genders. CONCLUSION: Lifting random unknown loads appears to alter kinematic responses, particularly for men. Women attempt to modify the effect of random unknown loads by changing the lifting style through alterations in upper limb motions (e.g., drag box toward them prior to lifting). However, a need remains for a more comprehensive biomechanical investigation (e.g., spine loading) into the effects of random unknown loads because many of the effect sizes were small. APPLICATION: Small kinematic adaptations resulting from tasks involving unknown and random loads may be mediated by the use of visual cues, order of presentation, or a change in lifting style.     

Changes in trunk muscle activation and lumbar-pelvic position associated with abdominal hollowing and reach during a simulated manual material handling task

The purpose of this study was to investigate the effect of abdominal hollowing (AH) on trunk muscle activation and lumbar-pelvic motion during a controlled lift and replace task. Surface electromyograms were recorded from five abdominal and two back muscle sites. Sagittal lumbar-pelvic motion was recorded by video. Subjects lifted a 3.8 kg load in normal, maximum and extreme reaches, first while performing their preferred lifting style (PLS) and then maintaining an AH technique. The external oblique muscle site activities were significantly higher (p < 0.05) for the AH technique (ranging from 7-20% of maximal voluntary activation (MVIC)) than at any of the abdominal sites for the PLS (ranging from 2-10% MVIC). Differences were found among abdominal sites for the AH, but not for the PLS. The back muscle site activities (ranging from 9-30% MVIC) were significantly higher (p < 0.05) than for any of the abdominal muscles for all conditions, except for the anterior external oblique for AH. The pelvic and lumbar angles changed significantly (p < 0.05) between normal and maximal reaches and between techniques. The AH technique altered abdominal muscle activation amplitudes, with minimal differences in trunk extensors compared to the PLS. The AH resulted in more posterior pelvic tilt.     

Hamstring stretching significantly changes the sitting biomechanics

The tightened hamstring connecting the tibia to the pelvis provides more posterior pelvic tilting and consequent backward curvature of the sacral and lumbar vertebrae. Therefore, the study goal was to quantitatively investigate the effect of hamstring and low back stretching on the trunk biomechanics in a system-level perspective. Twelve healthy subjects performed two stretching interventions (hamstring only (HS); hamstring + low back (HLS)) for 40 s on two separate days. They sat on a stool before and after the intervention while capturing trunk kinematics and EMG. In addition, the lumbar flexion angle at which the L4 paraspinals deactivate (i.e., flexion-relaxation phenomenon; FRP) was monitored while trunk flexion-extension trials, performed before and after the protocol. The FRP onset angle was captured to verify the biomechanical changes in the lower extremity and trunk systems. In the results, the stretching intervention significantly increased the reaching distance by 6.3 cm in the sit-and-reach test performed immediately before and after the intervention. The flexible hamstring improved the lumbar flexion angle and head postures in both the HS and HLS. However, the HLS induced laxity in lumbar passive tissues, as confirmed by changes in the FRP, and significantly increased co-activation in the low back. The stress-relaxation of the hamstring and surrounding passive tissues could help to maintain better lumbar flexion angle (i.e., lumbar lordosis) while sitting. Periodic HS for 40 s without any significant lumbar flexion may be recommendable for office workers who sit for long periods.