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PubMed1998

Scaling anticipatory postural adjustments dependent on confidence of load estimation in a bi-manual whole-body lifting task.

Anticipatory control of motor output enables fast and fluent execution of movement. This applies also to motor tasks in which the performance of movement brings about a disturbance to balance that is not completely predictable. For example, in bi-manual lifting the pick-up of a load causes a forward shift of the centre of mass with consequent disturbance of posture. Anticipatory postural adjustments are scaled to the expected magnitude of the perturbation and are initiated well before the availability of sensory information characterising the full nature of the postural disturbance. However, when the postural disturbance unexpectedly changes, the anticipatory adjustment of joint torques is not equilibrated and may result in a disturbance to balance. In a previous study, it was demonstrated that apart from anticipatory postural adjustments, corrective responses after load pick-up are used to further compensate the postural disturbance. In this study it was examined whether the central nervous system (CNS) assembles a strategy that incorporates both anticipatory control and corrective responses, in which the magnitude of the anticipatory postural adjustments depends on the perceived level of predictability of the postural disturbance. Subjects performed series of lifts in which the magnitude of the load was never revealed to the subject. Two boxes equal in size and colour, but different in mass (6 and 16 kg), were used. Differences in expectation were created by several lifts with the 16-kg load before the 6-kg box was presented. It was observed that the number of strong corrective responses (stepping) varied with the number of 16-kg trials that formed the prior experience when the final 6-kg trial was presented. The follow-up question was whether control relied more on anticipation in the stepping trials, compared with trials in which such gross signs of imbalance were absent. In this study it was shown that subjects when stepping (i) exhibited differential anticipatory postural adjustments in comparison with 6-kg trials in which expectation was not shaped by preceding 16-kg trials, and (ii) scaled the anticipatory postural adjustments similar to those preceding lift-off of the 16-kg trial preceding it. These findings emphasise the programmed nature of the anticipatory postural adjustments and the ability of the CNS to selectively tune the anticipatory postural adjustments to stored information gained during the previous lift(s).

Adaptation, Physiological↗
PubMed1998

Gender comparison of peak oxygen uptake: repetitive box lifting versus treadmill running.

The gender differences in peak oxygen uptake (VO2peak) for various modes of exercise have been examined previously; however, no direct gender comparisons have been made during repetitive lifting (RL). In the present study the VO2peak between RL and treadmill running (TR) was compared between 20 men [mean (SD) age, height, body mass and body fat: 21 (3) years, 1.79 (0.06) m, 81 (9) kg, 19 (6)%, respectively] and 20 women [mean (SD) age, height, body mass and body fat: 21 (3) years, 1.63 (0.05) m, 60 (7) kg, 27 (6)%, respectively]. VO2peak (l x min[-1]), defined as the highest value obtained during exercise to volitional fatigue, was determined using discontinuous protocols with treadmill grade or box mass incremented to increase exercise intensity. For RL VO2peak, a pneumatically driven shelf was used to lower a loaded box to the floor, and subjects then lifted the box, at a rate of 15 lifts x min(-1). VO2peak (l x min(-1) and ml x kg(-1) x min[-1]) and minute ventilation (VE, l x min[-1]) were determined using an on-line gas analysis system. A two-way repeated measures analysis of variance revealed significant gender effects, with men having higher values for VO2peak (l x min(-1) and ml x kg(-1) x min[-1]) and VE, but women having higher values of the ventilatory equivalent for oxygen (VE/VO2). There were also mode of exercise effects, with TR values being higher for VO2peak (l x min(-1) and ml x kg(-1) x min[-1]) and VE and an interaction effect for VO2peak (l x min(-1) and ml x kg(-1) x min[-1]) and VE/VO2. The women obtained a greater percentage (approximately 84%) of their TR VO2peak during RL than did the men (approximately 79%). There was a marginal tendency for women to decrease and men to increase their VE/VO2 when comparing TR with RL. The magnitude of the gender differences between the two exercise modalities appeared to be similar for heart rate, VE and R, but differed for VO2peak (l x min(-1) and ml x kg(-1) x min[-1]). Lifting to an absolute height (1.32 m for the RL protocol) may present a different physical challenge to men and women with respect to the degree of involvement of the muscle groups used during lifting and ventilation.

Adult↗
PubMed1992

Lumbar posterior ligament involvement during extremely heavy lifts estimated from fluoroscopic measurements.

The mechanical role of the lumbar posterior ligaments during lifting tasks remains controversial. This study was designed to assess the ligament and disc contribution in resisting trunk flexion moment during extremely heavy lifts performed by national class powerlifters. Direct measurements of lumbar vertebrae kinematics in sagittal plane were obtained from videofluoroscopy utilizing multiple digitizing, correction for optical distortions and digital filtering. Four experienced powerlifters executed three trials, resulting in about 72 mA s of total radiation exposure. In the first trial, joint angles were measured when subjects fully flexed their spines to a point where the passive tissues resisted the flexor moment creating myoelectric silence in the extensor musculature. Next, two conventional deadlift style lifts were executed with the barbell load ranging from 183.7 to 210.9 kg. Four vertebral corners were digitized at a sampling rate of 30 Hz. The relative intervertebral joint angles, distance between the ligament attachment points, shearing and compressive displacements were calculated from a rigid body motion approach. Analysis revealed that except for one trial of one subject, they accomplished their lifts with an amount of lumbar flexion between 1.5 and 13 degrees less than they demonstrated during full flexion. Resultant ligament lengths at the beginning of the lifts ranged from 56.1 to 99.8% of their lengths when the trunk was fully flexed. It was concluded that ligaments did not strain sufficiently to contribute substantial resistance to the trunk flexion moment, relegating this responsibility to the musculature.

Adult↗
PubMed1995

An EMG-assisted model of trunk loading during free-dynamic lifting.

One of the continuing challenges in biomechanics has been to assess loading of the spine during dynamic lifting exertions. A model was developed to accurately simulate multi-dimensional spinal loads and trunk moments from measured muscle coactivity and external forces during free-dynamic lifting exertions. Model validity was demonstrated by comparing measured and predicted trunk extension moments. Its purpose was to examine realistic representations of lifting kinetics, kinematics, and dynamic trunk mechanics that may influence spinal loading, and to demonstrate that EMG-assisted modeling techniques can be applied to the analysis of free-dynamic exertions. Spinal loads and trunk moments were predicted from the muscle force vectors and external loads. Muscle tensile forces were determined from the product of normalized EMG data modulated to account for contractile dynamics, muscle cross sectional area, and muscle force per unit cross-sectional area. Model output was physiologically valid, i.e. average predicted muscle force per unit cross-sectional area of 50-65 N cm-2, and accurately predicted measured, dynamic, lifting moments, with an average R2 = 0.81 in the sagittal plane and R2 = 0.76 in the lateral plane. Results indicated that compressive and shear loading increased significantly with exertion load, lifting velocity, and trunk asymmetry.

Abdominal Muscles↗
PubMed2005

An evaluation of methods assessing the physical demands of manual lifting in scaffolding.

Four methods assessing the physical demands of manual lifting were compared. The scaffolding job was evaluated and three distinct scaffolding tasks were ranked using: (1) the revised NIOSH lifting equation (NIOSH method), (2) lifting guidelines for the Dutch construction industry (Arbouw method), (3) rapid appraisal of the NIOSH lifting equation (practitioners' method), and (4) systematic observations. For the three first-mentioned methods the same dataset was used; observation took place in a different setting in the same company. At job level, all methods indicated that ergonomic interventions are required to protect scaffolders from an increased risk for low back pain. The NIOSH, Arbouw and practitioners' method resulted in a similar ranking order of tasks (transport>construction>dismantlement). In contrast, the observational method gave transport the lowest ranking. The underlying cause was probably that the observational method is more sensitive to durations of tasks and lifting within tasks than the three other methods.

Adult↗
PubMed2006

Reliability and agreement of 5 Ergo-Kit functional capacity evaluation lifting tests in subjects with low back pain.

OBJECTIVE: To assess interrater reliability and agreement of 5 Ergo-Kit functional capacity evaluation lifting tests in subjects with low back pain (LBP). DESIGN: Within-subjects design, with 2 repeated measurements. SETTING: Academic medical center in The Netherlands. PARTICIPANTS: Twenty-four subjects (10 men, 14 women) with LBP. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURE: Five Ergo-Kit lifting tests (2 isometric, 3 dynamic) were assessed on 2 occasions (t1, t2), by 2 different raters (R1, R2). The interval between the test sessions was 3 days. Interrater reliability level was expressed with the intraclass correlation coefficient (ICC), and the level of agreement between raters with the standard error (SE) of measurement. RESULTS: ICCs means (reliability) of isometric and dynamic Ergo-Kit lifting tests ranged from .94 to .97, and SE of measurement values (agreement) ranged from 1.9 to 8.6 kg. CONCLUSIONS: There was good reliability and agreement between raters of the isometric and dynamic Ergo-Kit lifting tests in subjects with LBP, which supports the use of these tests to assess functional lifting capacity.

Adult↗
PubMed2005

Differentiating lifting technique between those who develop low back pain and those who do not.

BACKGROUND: No research to date has been able to discriminate differences in lifting technique for healthy individuals who eventually develop low back pain compared to those that do not while employed in a manual materials handling industry. The purpose of this study was to demonstrate the ability of principal component analysis to identify differences in lifting technique. METHODS: Principal component analysis was applied to sixteen kinematic and kinetic waveforms describing the two-dimensional motion of the trunk and load. The principal component scores for each variable were used as the dependent measures in a one-way ANOVA to determine group differences. FINDINGS: Significant group differences (P<0.05) were found for five of the principal component scores capturing associated kinematic waveform patterns related to the control and placement of the box on the shelf, and associated kinetic waveform patterns related to the relative timing of extension moment generation in the sacral and thoracic regions. A related waveform pattern for trunk compression was also found. INTERPRETATION: Due to the coordinated movements involved in tasks such as lifting, differences among clinical populations have been difficult to demonstrate empirically. We were able to identify different characteristics in lifting kinematics and kinetics prior to the development of low back pain. Principal component analysis was able to identify important biomechanical differences where traditional analyses failed. This is the first study to identify such lifting differences prior to the development of low back pain.

Diagnosis, Computer-Assisted↗
PubMed2003

The effects of release height on center of pressure and trunk muscle response following sudden release of stoop lifting tasks.

BACKGROUND AND OBJECTIVES: Sudden release of load during lifting threatens postural stability and is countered by trunk muscle response, which can generate high loads on the spine, and may be a cause of tissue injury. The postural threat following sudden release and the consequent muscular response are likely to depend on the posture at the time of release. This study investigates the effects of sudden release of load at two release heights of one- and three-quarters of the knee to shoulder distance during stoop lifting. METHODS: Ten normal southern Chinese male volunteers were subject to sudden release of 20, 40, 60 and 80 N loads during stoop lifting trials. The release was randomly selected to be on the third, fourth or fifth cycle of a trial and was triggered at heights of one- and three-quarters of the total knee to shoulder lifting distance. The subjects stood on a force platform to allow the postural disturbance to be recorded by monitoring the center of pressure (COP), and electromyographic (EMG) data were collected from the rectus abdominus, internal oblique, external oblique, erector spinae and latissimus dorsi muscle groups. RESULTS: The COP excursion moved closer to the posterior limit of stability with increasing release load, and this effect was significantly more marked for release from the lower of the two heights. The minimum posterior COP separation from the posterior limit of stability was significantly less for the lower release height at all loads (p<0.001 in all cases). EMG data showed that the agonist-antagonist co-contraction durations were higher for the lower release height, and unlike sudden release from the higher level, showed a significant increase with increasing load. CONCLUSIONS: Sudden release at lower release height during stoop lifting results in significantly greater postural disturbance and spinal loading. The mean load predicted to result in fall or stumble at the lower release height (133 N) is significantly less than that predicted at the higher of the two release heights (245 N). A more marked effect of release load is also seen in the postural disturbance and trunk muscle co-contraction time for the lower release height, and particular care should therefore be taken when handling potentially unstable loads under these conditions. If the security of the load cannot be guaranteed, storage at a higher level may reduce the risk of injury due to sudden release of the load.

Adult↗
PubMed1999

Prompting correct lifting posture using signs.

The use of a symbol to prompt the adoption of correct lifting posture was examined in three studies. Study 1 used an Appropriateness Test to evaluate nine symbols designed to encourage the adoption of correct lifting posture. Four symbols met the appropriateness criteria and were tested for comprehension in Study 2. Study 3 examined the effect of the best performing symbol from Study 2 in a field setting which involved subjects lifting a small box. Results indicate significant increases in the adoption of the use of correct lifting posture when the symbol was present compared to a control condition. The study also identified the placement of a lifting criterion symbol onto packaging as a useful technique for communicating safety information.

Adult↗
PubMed1998

Is coordination of two-joint leg muscles during load lifting consistent with the strategy of minimum fatigue?

The purpose of this study was to examine if strong correlations reported for a back lift task between activity (EMG) of two-joint rectus femoris (RF), hamstrings (HA), and gastrocnemius (GA) and the difference in the joint moments could be predicted by minimizing an objective function of minimum fatigue. Four subjects lifted barbell weights (9 and 18 kg) using a back lift technique at three speeds normal, slow, and fast. Recorded ground reaction forces and coordinates of the leg joints were used to calculate the resultant joint moments. Surface EMG of five muscles crossing the knee joint were also recorded. Forces of nine muscles were calculated using static optimization and a minimum fatigue criterion. Relationships (i) (RF EMG-HA EMG) vs (knee moment hip moment) and (ii) GA EMG vs. (ankle moment knee moment) were closely related (coefficients of determination were typically 0.9 and higher). Qualitatively similar relationships were predicted by minimizing fatigue. Gastrocnemius and hamstrings had the agonistic action at both joints they cross during load lifting, and their activation and predicted forces increased with increasing flexion knee moments and extension ankle and hip moments. The rectus femoris typically had the antagonistic action at the knee and hip, and its activation and predicted force were low. Patterns of predicted muscle forces were qualitatively similar to the corresponding EMG envelopes (except in phases of low joint moments where accuracy of determining joint moments was presumably poor). It was suggested that muscle coordination in load lifting is consistent with the strategy of minimum muscle fatigue.

Ankle Joint↗
PubMed1999

The influence of trunk modelling in 3D biomechanical analysis of simple and complex lifting tasks.

OBJECTIVE: The purpose of this study was to evaluate different methods of estimating the body segment parameters and different methods of partitioning the trunk in order to reduce errors in the inverse dynamic analysis of lifting tasks. DESIGN: The same data set was used to evaluate moment errors associated to five linked models differing by the way the trunk was modelled. BACKGROUND: The inverse dynamic analysis of complex lifting tasks involving significant lower limb displacements requires the use of upper body linked models. However, the estimation of the body segment parameters of trunk segments and the flexible properties of the trunk can lead to errors when using this modelling approach. METHODS: Twenty-one male subjects performed four lifting tasks. Five cameras, two force platforms and a dynamometric box provided inputs to five tridimensional (3D) dynamic linked models. Three modelling parameters of the trunk were tested in these models: (1) the use of a geometric or a proportional anthropometric model to estimate the body segment parameters of the trunk, (2) the location of the antero-posterior position of the centre of mass of the trunk segments (at a percentage of the trunk depth vs on a line between hips and shoulders), and (3) the partitioning of the trunk in two or three segments. The behavior of these linked models was assessed with three different error analyses. RESULTS: The results revealed that all three modelling parameters of the trunk can reduce moment errors, especially when applied to subjects characterized by a larger abdomen. CONCLUSIONS: The inverse dynamic analysis of lifting tasks using an upper body modelling approach should take into consideration the interindividual variability inherent to the trunk morphology and non-rigidity. RELEVANCE: The trunk geometry and flexibility shows considerable variability among individuals. The use of upper body linked models requires adequate modelling of this segment to minimize errors in 3D inverse dynamic analysis of lifting tasks.

Adult↗
PubMed1999

Effects of kinematics constraints on hand trajectory during whole-body lifting tasks.

Trajectories of the hands and whole-body center of mass were studied during whole-body lifting tasks. The movements of different parts of the body were monitored with the ELITE system. Subjects were instructed to lift to shoulder height an object placed at one of two distances (5-45 cm) before them on the floor. The lifts were performed both with and without kinematics constraints (i.e. to produce a straight hand trajectory while lifting, and to lift without any instructions, respectively). Hand trajectories were roughly straight when performed under the constrained condition, but curved when performed without instruction. Hand velocity curves showed bell-shaped profiles. In both groups, body centers of mass (whole-body, upper and lower part) were calculated and their trajectories showed invariant sagittal displacements. These results support the idea that movement contributes to postural control and, reciprocally, that whole-body center of mass is a robust and controlled variable which plays an important role in hand trajectory formation.

Adult↗
PubMed2002

Test-retest reliability of lifting and carrying in a 2-day functional capacity evaluation.

The objectives of this study were to establish test-retest reliability of lifting and carrying of a functional capacity evaluation (FCE) on two consecutive days and to verify the need for a 2-day protocol. A cohort of 50 patients (39 men, 11 women) with nonspecific low back pain were evaluated using a 2-day FCE protocol. Intraclass correlation coefficients (ICC) were calculated for weight lifted and carried. Predictive relationships between test and retest were explored by means of a regression analysis. The results of ICC were lifting low 0.87, lifting overhead 0.87, and carrying 0.77. Performances on day 2 were on an average 6-9% higher. Other than the amount of weight handled on day 1, no variable was found to predict performance on day 2. It was concluded that test-retest reliability of lifting and carrying was good, and the need for a 2-day protocol could not be confirmed.

Adult↗
PubMed2004

The concurrent validity of the ERGOS Work Simulator and the Ergo-Kit with respect to maximum lifting capacity.

The aim of this study was to investigate the concurrent validity--as regarding maximum lifting capacity--between the Functional Capacity Evaluation (FCE) methods, ERGOS Work Simulator and Ergo-Kit. Twenty-five healthy, male firefighters participated. Dynamic lower and upper lifting capacities were determined using both FCE methods. Paired t tests showed the mean maximum lifting capacities to be significantly higher statistically when determined by the Ergo-Kit for lower, as well as, upper lifting. Spearman rank correlation coefficients varied between 0.49 and 0.66. It was concluded that the concurrent validity for lifting between both FCE methods was poor.

Adult↗
PubMedDate not supplied

[Is the orthopedically correct lifting technique rational from a cardiopulmonary and metabolic viewpoint?].

INTRODUCTION: In spite of educational work for many years by the orthopaedic surgeons wrong lifting techniques are still used in everyday life as well as during exercise. The reason for this could be the fact that there is an advantage regarding these techniques from the energetic point of view. MATERIAL AND METHODS: To clarify this issue we examined 30 healthy males within the age range of 17 and 30 years (weight: 74.0 +/- 9.2 kg, height: 182.5 +/- 6.7 cm). In a randomised sequence the volunteers carried out two different lifting techniques: 1. Lifting with stretched legs and bent back, 2. Lifting with bent legs and stretched back (Brügger technique). The test scheme consisted of four different 3-minute exercise levels with increasing weights (0 kg, 5.2 kg, 12.1 kg, 19.2 kg), the repetition rate was 30 times per level. RESULTS: Using the Brügger technique the results for heart rate, VO2, VCO2 and VE were highly significant (p < 0.001) above the results of the other technique at all exercise levels. On the RPE (rate of perceived exertion) scale the differences were statistically significant regarding the 0.01-level. CONCLUSION: The results give rise to the supposition that the energy consumption for the lifting technique with the bent back is lower and is therefore preferred in everyday life and during exercise. These findings should be taken into consideration when informing people about possible damages.

Adolescent↗
PubMed2004

Estimation of lifted weight and produced effort through perception of point-light display.

It has been shown that human observers can estimate the weight of a box from the observation of a point-light display of a lifting motion. We asked observers to report the weight of the box and the effort produced by five lifters ranging in size and strength to determine if observers can perceive lifter size. In experiment 1, five or six weights from each of five lifters were shown to fourteen observers in a random order. Observers showed less error in estimating the amount of effort each lifter produced than in estimating the actual weight of the box. In experiment 2, the lifters were presented individually to forty observers to remove any effect observing a previous lift might have had on estimating the subsequent lift by a different lifter. The results showed an improvement in estimated weight but not in estimated effort. In experiment 3, the actual size of the lifters was given to thirty-four observers, and the estimations of both weight and effort improved. In experiment 4, observers did not improve when observing practice trials and estimating either only weight or only effort. The results from the four experiments suggest that observers are more sensitive to lifter's effort than to the weight lifted, and that observers tend to use changes in the velocity profile of the lift when making their estimates.

Adult↗
PubMed2002

Effects of posture on dynamic back loading during a cable lifting task.

This study evaluated spinal loads associated with lifting and hanging heavy mining cable in a variety of postures. This electrical cable can weigh up to 10 kg per metre and is often lifted in restricted spaces in underground coal mines. Seven male subjects performed eight cable lifting and hanging tasks, while trunk kinematic data and trunk muscle electromyograms (EMGs) were obtained. The eight tasks were combinations of four postures (standing, stooping, kneeling on one knee, or kneeling on both knees) and two levels of cable load (0 N or 100 N load added to the existing cable weight). An EMG-assisted model was used to calculate forces and moments acting on the lumbar spine. A two-way split-plot ANOVA showed that increased load (p < 0.05) and changes in lifting posture (p < 0.05) independently affected trunk muscle recruitment and spinal loading. The increase in cable load resulted in higher EMG activity of all trunk muscles and increased axial and lateral bending moments on the spine (p < 0.05). Changes in posture caused more selective adjustments in muscle recruitment and affected the sagittal plane moment (p < 0.05). Despite the more selective nature of trunk EMG changes due to posture, the magnitude of changes in spinal loading was often quite dramatic. However, average compression values exceeded 3400 N for all cable lifting tasks.

Adult↗
PubMed2004

Postural and trunk muscle response to sudden release during stoop lifting tasks before and after fatigue of the trunk erector muscles.

The effect of fatigue on the muscular and postural response to sudden release of different stoop lifting loads was studied. Ten male volunteers performed a series of stoop lifting trials before and after fatigue of the erector spinae. Trials were performed using loads of 20, 40, 60, and 80 N, and sudden release of load was triggered randomly on one of the repetitions using an electromagnetic release. The onset of release was registered by an accelerometer, centre of pressure (COP) motion was recorded via a forceplate, and EMG activities of the latissimus dorsi (LD), erector spinae (ES), rectus abdominus (RA), external oblique (EO) and internal oblique (IO) muscles were recorded. A slightly reduced lifting speed was seen after fatigue, particularly at the higher loads, but this had little effect on the perturbing force at release, which was dominated by the release load. A significant effect of fatigue was seen on the antero-posterior COP motion, with the postural disturbance being decreased after fatigue. Fatigue resulted in a significant increase in ES (p = 0.029) and LD (p = 0.015) relaxation times and, while the response patterns (relaxation, contraction or no response) of the anterior trunk muscles (RA, EO, IO) were not always consistent, the proportion of response by relaxation was greater after fatigue. This resulted in a lower incidence but longer duration of co-contraction of the ES-RA, ES-EO and ES-EO muscle groups following fatigue, such that the mean co-contraction duration of these groups showed no significant differences before and after fatigue. The response to sudden release is a balance between maintaining postural stability and at the same time preventing the trunk musculature from overloading the spine and risking tissue injury. While fatigue of the trunk extensors does not appear to increase either the risk of fall or stumble or the incidence of co-contraction following sudden release of stoop lifting tasks, the duration of co-contraction appears to increase following fatigue. Further study is required to quantify the loading on the spine during sudden release of different lifting tasks before and after more realistic fatigue conditions.

Abdominal Muscles↗