Micheline Gagnon

The influence of dynamic factors on triaxial net muscular moments at the L5 S1 joint during asymmetrical lifting and lowering

Asymmetrical lifting and lowering are predominant activities in the workplace. Mechanical causes are suggested for many back injuries and the dynamic conditions within which spine loading occurs are related to spine loading increase. More data on tridimensional biomechanical lumbar spine loading during asymmetrical lifting and lowering are needed. A tridimensional dynamic multisegment model was developed to compute spinal loading for asymmetrical box-handling situations. The tridimensional positions of the anatomical markers were generated by a direct linear transformation algorithm adapted for the processing of data from two real and two virtual views (mirrors). Two force platforms measured the external forces. Five male subjects performed three variations (slow, fast and accelerated) of asymmetric lifting and two variations (slow and fast) of asymmetric lowering. The torsional, extension/flexion and lateral bending net muscular moments at the L5/S1 joint were computed and peak values selected for statistical analysis. For the lifting task, the fast and accelerated conditions showed significant increases over the slow condition for torsion, extension/flexion and lateral-bending moments. The accelerated condition also showed significant increases over the fast condition for extension. A comparison between lifting and lowering tasks showed equivalent loadings for torsion and extension. The moments were compared to average maximal values measured on equivalent male subject populations by isokinetic dynamometry. This showed torsional and extension values of 30 and 83% of the maximal possible subject capacity, respectively. These results demonstrated that dynamic factors do influence the load on the spine and highlighted the influence of both lifting and lowering on the loading of the spine. This suggested that for a more complete analysis of asymmetrical handling, the maximal velocity and acceleration produced during lifting should be included.

Validation of two 3-D segment models to calculate the net reaction forces and moments at the L(5)/S(1) joint in lifting.

The purpose of this study was to examine the validity and sensitivity of two three-dimensional segment models to estimate the net reaction forces and moments at the L(5)/S(1) joint. The two dynamic three-dimensional multisegment models, applied to lifting activities, were a lower body model and an upper body model. Three healthy male subjects participated in this study. The asymmetrical task consisted of lifting a load of 9.6 kg in a normal speed condition and in a fast condition. Results from the two models in terms of joint reaction forces and joint reaction moments at L(5)/S(1) were compared and were then used to validate them. The correlation between the reaction moments from both models were generally above 0.95 and the root mean square (RMS) differences were generally below 10 Nm but could reach 38 Nm. Similar trends were observed in the sensitivity analysis. A proportion of the error was attributable to errors in the segment accelerations because of an increase in the RMS differences between the models with an increase in lifting speed. The use of the lower body model seemed to present some advantages over the upper body model because of the nature of the task analysed which did not require large accelerations from the lower part of the body.

Muscular mechanical energy expenditure as a process for detecting potential risks in manual materials handling

The problem of injuries in manual materials handling remains a big concern in industrialized countries. It has become imperative in occupational biomechanics to extend the analyses to all pertinent factors involved in working tasks and to adopt an experimental approach leading to the understanding of the relative demands imposed simultaneously on all body joints. The evaluation of joint muscular work and the processes of energy generation, absorption and transfer appears promising as a tool in the detection of risk factors in working tasks. The present study consisted of evaluating two tasks (lifting and lowering) performed at five different heights (from 15 to 185 cm) with five different loads (from 3.3 to 22.0 kg). The subjects were eight experienced workers from a food product warehouse. Cinematography techniques and two AMTI force platforms were used to collect the data. Dynamic and planar segmental analyses were performed to calculate the net muscular moments at the joints, and work was calculated from the integration of muscular power. Factorial analyses of variance with repeated measures were performed on the dependent variables to evaluate the main effects of tasks, loads, and heights (for lifting and for lowering) and the interactions. The results revealed the adoption of different movement strategies in the handling of heavier loads. In the first, a larger emphasis of energy transfer and movement economy; in the second, a reduction in the relative contribution of the shoulders to the detriment of an increased participation of the lower back and hips was found. The comparison between lifting and lowering tasks indicated that lifting was only slightly more demanding than lowering for maximum muscular moments (about 15%) but much more so for mechanical work (about 40%); however, the nature of the efforts in eccentric contractions suggests that the lowering of heavy loads may be risky. Finally, the results revealed the deviation of height of handling from the waist level to be a significant factor. Handling at lower heights was considerably more demanding but the work was shared by several joints, mainly by the hips and lower back (about 70%); on the other hand, in handling above the waist, the work efforts were concentrated on the upper limbs (about 80%). In most cases, the participation of lower limbs was minimal and some movement strategies are suggested for future research.

Manual handling techniques: Comparing novices and experts

Abstract The purpose of this study was to compare the techniques used by six expert handlers and six novices during a free handling task. Each subject had to transfer three sets of 16 boxes from a platform to a four-wheel cart. The observations dealt with the position of the subject at the beginning of transfer and at deposit (position of the back, knees and feet, pelvic orientation, position of the hands), his way of moving during the transfer (position of the feet) and his way of positioning and moving the box during handling (tilt). The results show that the expert handlers chose handling techniques rather different than those of the novices, particularly with regard to the position of the knees, feet and pelvis, the location of the grip, the movement of the feet during transfer, and the position of the box during handling. The study suggests that the strategies adopted by the experts would improve balance, and permit better control of the load and more efficient use of box momentum during transfer.

Evaluation of forces on the lumbo-sacral joint and assessment of work and energy transfers in nursing aides lifting patients

Tasks associated with patient handling may present nursing aides with some risk of injuring the lumbar spine. The purpose of this study was to estimate the forces at L5/S1 and to assess mechanical work and energy transfers in a task consisting of raising a patient (a 72·6thinsp; kg manikin) from a chair using three different methods: (A) with the hands; (B) with the forearms behind the patients back at shoulder level; and (C) with a belt held at waist level. Six male subjects took part in the experiment. Spinal forces were estimated from a static and planar mathematical model used in conjunction with cinematography techniques, a force platform and EMG recordings. External forces and the internal forces (compression and shear at L5/S1) were determined from free-body diagrams and static equations. The model was analysed for its sensitivity in estimating patterns of EMG forces, intra-discal and musculo-ligamentous forces, intra-abdominal pressure and inertial forces. The model was found to discriminate betw...

Lumbo-sacral loads and selected muscle activity while turning patients in bed

Handling patients in bed using a pique (a waterproof padded sheet placed under the patient) is associated with a high incidence of risks for the spine with, in particular, the activity of pulling and turning the patient with the pique representing the highest risk. Fifteen female nursing aides were evaluated for compression and shear forces at the L5/S1 joint and for selected muscular activities in the trunk and shoulders. Films, force platforms and EMG recordings supplied the data; dynamic segmental analyses were performed to calculate reaction forces at L5/S1, and a planar single-muscle equivalent was used to estimate internal loads. Different execution parameters were examined including execution velocity, height of bed, direction of effort, leg position and knee support. A ‘free’ task, and a manual task not involving the pique, were also investigated. Recommendations are made for reducing spinal loading. The results also suggest that a change of direction in the trunk motion may present some risks whe...

Pivoting with the load : an alternative for protecting the back in asymmetrical lifting

The purpose of this study was to examine different lifting conditions with combined flexion and twisting of the trunk relative to the pelvis (full twist and half-twist techniques) and to compare them to a situation using feet pivoting with minimization of trunk motions relative to the pelvis. Nine subjects with limited experience were tested with two force platforms and two 16-mm cameras coupled with two mirrors; dynamic three-dimensional multisegment models were constructed and the net muscular moments as well as the angular velocities of the trunk relative to pelvis were determined about the three orthogonal orthopaedic axes of the trunk at L5-S1 in flexion-extension, lateral bending, and twisting. The results showed that pivoting required larger extension moments but considerably smaller twisting moments and that these moments were exerted from a safer trunk posture. Pivoting appears to be a good compromise to avoid or minimize complex trunk postures and loadings.

Biomechanical exploration on dynamic modes of lifting

Whatever the lifting method used, dynamic factors appear to have an effect on the safe realization of movement, and NIOSH guidelines recommend smooth lifting with no sudden acceleration effects. On the other hand, inertial forces may play an important role in the process of transfer of momentum to the load. The direction by which these inertial forces may affect the loadings on body structures and processes of energy transfers cannot be determined a priori. A biomechanical experiment was performed to examine if there were differences in the execution processes between a slow-continuous lift and an accelerated-continuous lift, and also between accelerated lifts either executed continuously or interrupted with a pause. The lifts were executed from a height of 15 cm to a height of 185 cm above the head and with two different loads (6.4 and 11.6 kg). Five experienced workers in manual materials handling were used as subjects. Films and force platforms recordings supplied the data; dynamic segmental analyses were performed to calculate net muscular moments at each joint; a planar single-muscle equivalent was used to estimate compression loadings at L5/S1; total mechanical work, joint work distribution, and energy transfers were determined from a kinetic approach based on the integration of joint power as a function of time. Analyses of variance with repeated measures were applied to the three treatments. The results showed that joint muscular moments, spinal loadings, mechanical work, and muscular utilization ratios were generally increased by the presence of acceleration without inducing benefits of improved energy transfers; therefore slower lifts with reduced acceleration may be safer when handling moderately heavy loads. The maximum values of kinematic and kinetic factors were generally not affected by the pause, but the occurrence of jerks in the movement (acceleration, ground forces, and muscular moments) suggests that the pause may not be indicated when considering total exposure to muscular exertion. Full consideration should be given to the dynamics of motion when assessing risk factors in working tasks.

A geometric model of the lumbar spine in the sagittal plane

This article describes a geometric model using the skin profile and five anthropometric measurements to estimate the position of S1, T12, and all lumbar vertebrae for all postures assumed in the sagittal plane. This method involves a normalization process by which different skin profiles can be compared between postures and individuals. The skin profile is transformed by taking the differences with the lumbar spine into consideration. The model was developed and validated with 20 and 7 subjects, respectively. An error analysis shows an adequate level of accuracy for the absolute (1.68-1.82 cm)and relative(0.32-0.54cm) linear positions of vertebrae as well as their absolute (2.6-6.7°) and relative (1.4-3.6°) angular positions except for T12; however, the validity of the model was limited to specific angular motions in flexion for the pelvis (12±3%), the entire lumber spine. (14±13%) and the intervertebral motion of L4/L5(13±10%). The data obtained are very useful, especially in models designed to evaluate loadings on the lumbar spine.

Box tilt and knee motions in manual lifting: two differential factors in expert and novice workers

OBJECTIVE: It was the objective of this study to investigate the kinematic and kinetic effects of two specific handling factors that differentiate expert and novice workers, namely the level of knee flexion and box tilt. DESIGN: Seven inexperienced subjects were required to lift a 12-kg box in the sagittal plane using three different strategies: (1) reduced knee flexion and a backward box tilt (more typical of experts); (2) large knee flexion and a backward box tilt; (3) large knee flexion and no box tilt (more typical of novices). BACKGROUND: The lifting techniques of highly skilled workers differ substantially from those of novices but only limited information is available to compare their biomechanical differences. METHODS: The methods included dynamic segmental analyses to calculate the net moments at all body joints and a planar single-muscle equivalent to estimate compression loadings at L5/S1; total work and joint work distribution were calculated using the integration of joint power. The 3-D kinematic data were acquired with three video cameras and force data were obtained with one AMTI force platform which were synchronized with the film data. RESULTS: Box tilt reduced the load trajectory and loadings on the lower back and shoulders; a reduced knee flexion affected body posture and reduced mechanical work and loadings on all body joints. The combination of these two factors, box tilt and reduced knee flexion, showed added effects for almost all variables. CONCLUSIONS: These two factors proper to experts were, in this context, biomechanically more advantageous.