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PubMed2004

Impairment of a cortical event-related desynchronisation during a bimanual load-lifting task in children with autistic disorder.

In autism, the abilities of communication are affected, associated with abnormalities of cognitive, sensorial and motor development. In a previous study based on a load-lifting task, we showed impairment of anticipation in children with autism as evidenced by kinematics and eletromyographic recordings [Neurosci. Lett. 348 (2003) 17]. In the present study, we assessed the cortical counterparts of the use of anticipatory postural adjustments in a group of control children and in a group of children with autism. The tasks required maintaining a stable forearm position despite imposed or voluntary lifting of an object placed either on the controlateral forearm or on a support. We investigated the differences between the two groups of children on the Event-Related Desynchronisation (ERD) which precedes movement onset in adults [Electroencephalogr. Clin. Neurophysiol. 46 (1979) 138]. Electroencephalogram (EEG) power evolution of a 6-8-Hz frequency band was averaged before and after imposed or voluntary movement onset. EEG reactivity of control and autistic children did not differ during the imposed unloading condition, but significant differences appeared in the voluntary unloading situations. Before lifting the object, control children showed an ERD above the left motor areas. An ERD also occurred above the right motor areas when the object was placed on their forearm. This indicates that the ERD can also translate the use of anticipatory postural adjustments. By contrast, children with autism did not show an ERD in the two voluntary situations. This suggests a central deficit of anticipation in both postural and motor control in children with autism.

Autistic Disorder↗
PubMed1998

Accuracy of measurements for the revised NIOSH lifting equation. National Institute for Occupational Safety and Health.

Twenty-seven non-ergonomists who participated in a one-day training session on the use of the NIOSH lifting equation (NLE) were subsequently tested on a simulated lifting task eight weeks later to determine their accuracy in measuring the variables. Analysis of the results indicate that (1) inter-observer variability was small, especially for the most important factor (i.e. horizontal distance); (2) individuals can be trained to make measurements with sufficient accuracy to provide consistent recommended weight limit and lifting index values; and (3) measurement of the coupling and asymmetric variables were the least accurate.

Educational Measurement↗
PubMed1997

A method for measuring external spinal loads during unconstrained free-dynamic lifting.

Biomechanical lifting models often require the knowledge of the applied trunk moments and forces for model validation purposes and/or to determine loading levels experienced at various joints of the body. Trunk kinetic data under dynamic exertions are commonly difficult to attain without restrictive anatomic/anthropometric assumptions and cost or constraining body motion. The main objectives of the study were to present a new technique for determining continuous three-dimensional forces and moments about the L5/S1 spinal joint, and to validate the technique and assess its applicability under lifting situations. A combination of a force plate and two electrogoniometers facilitated the determination of trunk kinetics about L5/S1. An apparatus was devised to allow the application of various actual moments that were compared to their corresponding predicted moments. The results showed that, over all the conditions considered, the average percent error in estimating the actual applied moment(s) was about 4% (2.3 S.D.), with a test-retest reliability approaching unity. Given such agreement, along with the relative ease and directness of the method, it is believed that this approach should be applicable under most lifting conditions. The technique offers a fairly accurate measure of trunk moments without the need for constraining the motion of any body joint.

Biomechanical Phenomena↗
PubMed2001

Mechanical load on the low back and shoulders during pushing and pulling of two-wheeled waste containers compared with lifting and carrying of bags and bins.

OBJECTIVE: Compare the mechanical load on the low back and shoulders during pushing and pulling a two-wheeled container with the load during lifting and carrying the same amount of waste. BACKGROUND: Only little is known about risk factors and mechanical loads during push/pull operations. DESIGN: A complete 2(3) factor push/pull experiment. A two-wheeled container with 25 or 50 kg was pushed in front of and pulled behind the body by seven waste collectors. Further, the same subjects lifted and carried a paper bag and a dustbin both loaded with 7 and 25 kg. METHOD: All operations were video recorded and the push/pull force was measured by means of a three-dimensional force transducer. Peak Motus and Watbak software were used for digitising and calculation of torque at L4/L5 and the shoulder joints and compression and shear forces at L4/L5. RESULTS: During pushing and pulling the compression at L4/L5 is from 605 to 1445 N. The extension torque at L4/L5 produced by the push/pull force is counteracted by the forward leaning of the upper body. The shear force is below 202 N in all situations. The torque at the shoulders is between 1 and 38 Nm. CONCLUSION: In the present experiments the torques at the low back and the shoulders are low during pushing and pulling. No relation exists between the size of the external force and the torque at the low back and the shoulder. RELEVANCE: Pushing and pulling are common in many workplaces and have often replaced lifting and carrying situations. This has emphasised the need for more knowledge of the internal mechanical load on the body during these activities.

Adult↗
PubMed2003

Specific phase related patterns of trunk muscle activation during lateral lifting and lowering.

AIM: Lateral bending of the trunk has been demonstrated to be a risk factor in connection with injuries to the spine and its surrounding tissues. Adequate co-ordination of muscle controlling movement and stabilization of the trunk is essential to avoid injury. However, little is yet known about the responses of the lumbar trunk muscles during lateral lifting and lowering. The present investigation was therefore designed to study these responses. METHODS: In six subjects performing lateral lifting and lowering of different loads (0-40 kg) held laterally in one hand, the activities of eight trunk muscles were recorded using intramuscular electrodes. In addition, the angular motion of the trunk from side to side was measured from video recordings. Electromyographic amplitudes on both the contra- and ipsi-lateral sides (ipsi = towards the loaded hand) were analysed in relation to defined phases of trunk motion. RESULTS: Three periods of trunk muscle activation were generally observed, two from the contralateral muscles at the beginning and end of the motion and one from the ipsilateral muscles during the mid-part of the motion. The activities of the contralateral muscles increased, whereas the activities of the ipsilateral muscles decreased with increasing load. The degree of bilateral co-activation was greater in ventral than in dorsal muscles, in lowering compared with lifting, and in no-load or low-load compared with heavy load conditions. CONCLUSION: The co-ordination of trunk muscle activations during side-to-side trunk movements is dependent on trunk position and load. It is speculated that ventral muscles, particularly the oblique and transverse abdominal muscles, are relatively more involved than the other trunk muscles in trunk stabilization, especially in connection with lowering of a light hand-held load.

Abdominal Muscles↗
PubMed2001

Reaching-lifting-placing task during standing after stroke: Coordination among ground forces, ankle muscle activity, and hand movement.

OBJECTIVE: To investigate the coordination among hand movement, ground forces, and muscle activity in standing stroke patients reaching forward and lifting an object from a table. DESIGN: Survey. SETTING: Research laboratory. PATIENTS: Eight stroke patients and 8 persons serving as controls. MAIN OUTCOME MEASURE: Symmetry of percentage of body weight (BW) during initial standing, velocity and hand path trajectory, ankle muscle electromyography. Temporal and spatial parameters in percentage of movement time were recorded by using 2 forceplates, 3-dimensional kinematics, and surface electromyography. Motor function, sensory function, and functional performance were also assessed. RESULTS: Weight distribution during initial standing was significantly higher (57.4% +/- 8.1% BW) on the nonparetic leg. All subjects had preserved the preparatory loading phase, and after onset of hand movement loading shifted to the contralateral leg. Ankle muscle activity onset (lateral gastrocnemius [LG]) occurred after loading. In stroke subjects, LG was consistently activated first in the nonparetic leg, regardless of which arm performed the task. During paretic hand task, the reaching phase was significantly longer and the lifting phase significantly shorter compared with that of the nonparetic hand task and with that of the controls. In the paretic task, the hand path velocity was not bell-shaped; the object lifting was. CONCLUSIONS: Stroke subjects preserve the coordination between ground forces and hand movement. The lack of spontaneous use of the paretic hand is primarily caused by difficulties of planning the hand trajectory in space, as reflected by temporal and spatial parameters during task performance.

Activities of Daily Living↗
PubMed2000

The upper range of lumbar spine bone mineral density? An examination of the current world record holder in the squat lift.

Weight-bearing exercise is known to improve bone mineral density, however, excessive forces exerted on the lumbar spine can be pathologic. Cadaveric studies have calculated a hypothetical "critical compression force" at which the lumbar spine would suffer collapse. In addition, recent studies have suggested that bone density correlates with strength. Thus far studies have failed to examine elite power athletes to determine the possible upper range for bone mineral density and critical compression force. Therefore, we recruited the current world record holder in the squat lift, with a record squat lift >469 kg, for an examination of lumbar spine bone mineral density. The subject had dual energy x-ray absorptometry (DEXA) and magnetic resonance imaging (MRI) performed of the lumbar spine. The subject also had serum chemistries, cell blood count and testosterone levels performed. DEXA scan revealed the highest bone mineral density reported to date. MRI revealed normal alignment, no evidence of disc herniation or compressive disc disease. There was no frank or neural foraminal canal stenosis. The estimated compressive force generated on his lumbar spine during the squat lift of > 469 kg doubles the previously reported critical compression force. This case study supports the previously described relationship between strength and bone density and redefines the upper limits of bone density in strength athletes.

Absorptiometry, Photon↗
PubMed2001

Gender differences in lifting technique.

The importance of different motion patterns in the assessment of work technique is rarely addressed in the literature and even less information can be found regarding gender differences. In this study the possible gender differences in lifting technique from lifting experiments on 12 female and 10 male participants were examined. The participants performed squat and stoop lifts of a box. Movements were measured by means of opto-electronic measurement systems. Kinematic data derived from the measurements revealed some differences between the men and the women, e.g. in trunk motion and knee angle ranges. The hip-knee interjoint coordination was more synchronized for women than for men in terms of the relative phase angle. It is concluded that so far gender differences in motion patterns have not been sufficiently explored and that men and women need to be considered separately in the evaluation of work technique in manual handling tasks. Advantages and disadvantages of different coordination patterns need to be further investigated.

Adult↗
PubMed2004

The effect of feedback training on lumbosacral compression during simulated occupational lifting.

This study measured the effect of a feedback training program on lumbar compression during simulated occupational lifting. Two distinct types of feedback were compared: real-time electromyographic feedback, vs. an acceleration index delivered verbally post-lift. Kinematic data were collected from 28 subjects during symmetrical sagittal plane lifts. Following a baseline session, two feedback training sessions were provided, with a 1-week interval between each session. A control group followed the same protocols, but without receiving feedback training. A post-training session, using protocols identical to the baseline session, was used to assess pre-to-post changes in the dependent variable: peak lumbosacral compression computed using a dynamic linked-segment model. All three groups showed reductions in peak compression from pre-to-post: on average the control group improved by 11.2%, the EMG group by 16.7%, and the acceleration group by 25.3%. The results revealed an interaction between the improvement and the group (p=0.023), and a difference between the improvement in the control group and that in the verbal acceleration feedback group (p<0.01). These reductions in lumbosacral compression persisted after a 7-day interval without feedback training, suggesting that this approach could provide sustained risk-reduction during manual materials handling.

Acceleration↗
PubMed2005

Load spatial pathway and spine loading: how does lift origin and destination influence low back response?

While heavy lifting has been identified as an important risk factor for low back disorders, little is known about workplace spatial layout - the relative positions of shelves and the impact of this on spine loads. The objective of the current study was to investigate how the relative positions of the load origin and destination impact three-dimensional spine loads. Seven females and seven males lifted an 11.4 kg box from an origin shelf to a destination shelf, each defined by height (elbow, knee and shoulder level) and asymmetry (60 degrees clockwise, sagittally symmetric, 60 degrees counter-clockwise) while their spine loading was assessed by an electromyographic-assisted model. The results indicated that the starting and destination heights and starting task asymmetry all had significant impact on spine compression (with an increase of between 400 and 1900 N when compared to the most neutral position) and lateral shear (with a 100 to 150 N increase) while the destination height impacted the anterior - posterior shear forces (with up to 400 N increase). The results of the current study emphasize the importance of proper workplace spatial layout, specifically the importance of specifying starting position of the load relative to the destination. Adjustment of the starting position will impact the three-dimensional spine loads while the destination height and asymmetry influence the shear forces. Furthermore, the influence of the specific pathway (origin relative to destination) indicates there may be a potential preparatory muscle response leading to the loads on the spine. Thus, the pathway of the box plays an important role in the spine responses during lifting, in that longer and non-neutral pathways increase spine loads - indicating the importance of the relative position of the origin and destination shelf.

Accidents, Occupational↗
PubMed1999

Effect of gloves on prehensile forces during lifting and holding tasks.

The effect of gloves on the spatio-temporal characteristics of prehensile forces during lifting and holding tasks was investigated. Participants (n = 10) lifted a force transducer equipped object (weight = 0.29 N) with various types of gloves and barehanded using a two-fingered precision grip. Rubber surgical gloves of varied thicknesses (0.24, 0.61 and 1.02 mm) were worn to examine the effect of glove thickness on a rayon surface. It was found that grip force increased with thickness because the participants employed a higher safety margin above the minimum force required to hold the object. The safety margin for the barehanded condition was the smallest. The performance time for lifting the object was not influenced by the variation of glove thickness. The findings suggest that glove thickness, which presumably modifies the cutaneous sensation, influences grip force regulation. The effect of glove material (rubber and cotton) was also examined in relation to slippery (rayon) and non-slippery (sandpaper) surfaces. It was found that the participants used a larger grip force with the cotton glove than the rubber glove for the slippery surface, but not with the non-slippery surface. With use of the rubber glove, a relatively low grip force level was maintained for both slippery and non-slippery surfaces. The performance time for the cotton glove was longer than that for the rubber glove. The findings suggest that the rubber glove provides better efficiency of force and temporal control than the cotton glove in precision handling of small objects.

Adolescent↗
PubMed1999

The effectiveness of commonly used lifting assessment methods to identify industrial jobs associated with elevated risk of low-back disorders.

Low-back disorders (LBD) continue to be the most costly and common musculoskeletal problem facing society today. Investigators have developed tools or measures that are intended to identify jobs that will probably be associated with an elevated risk of low-back disorders. However, an important and not widely discussed issue associated with these tools and procedures has been that of the validity or effectiveness of the tools. Therefore the objective of this study was to evaluate the validity and effectiveness of two commonly used types of LBD assessment methods in terms of their ability to correctly associate jobs with LBD risk. The 1981 NIOSH Work Practices Guide for Manual Lifting and the 1991 NIOSH revised lifting equation, along with psychophysical measures were assessed for their ability to correctly identify high-, medium-, and low-risk (of LBD) jobs. Risk was defined according to a database of 353 industrial jobs representing over 21 million person-hours of exposure. The results indicated that both NIOSH measures were predictive and resulted in odds ratios between 3.1 and 4.6. Higher odds ratios were found when the maximum horizontal distance was used to assess a job compared to the average horizontal distance. Further analyses indicated that the two NIOSH assessment methods classified risk in very different ways. The 1981 NIOSH Guide demonstrated good specificity (91%) in that it identified low-risk jobs well but it also displayed low sensitivity by only correctly identifying 10% of the high-risk jobs. The 1993 NIOSH revised lifting equation, on the other hand, had better sensitivity. It correctly identified 73% of the high-risk jobs but did not identify low- and medium-risk jobs well. Using psychophysical criteria it was observed that 60% of the high-risk jobs would be judged to be acceptable, whereas, 64% and 91% of the medium- and low-risk jobs, respectively, would be judged to be acceptable. This study indicates that the different measures have various strengths and weaknesses. When controlling for occupational LBD it should be recognized that a variety of measures exist and that the measure that most appropriately assesses risk depends upon the characteristics of the job.

Databases, Factual↗
PubMed1996

Load Acceleration and Footstep Strategies in Asymmetrical Lifting and Lowering.

Accelerated execution effects for lifting and lowering a 12-kg box using two footstep strategies associated with experienced workers were studied. Eight healthy male participants performed a normal and an accelerated execution of a lifting task and a lowering task, using a minimal feet displacement strategy (oblique-step) and a strategy with a step (crossed-step). It was hypothesized that the accelerated executions, as compared to the normal executions, would have a different effect on L5/S1 resultant moment, body posture, and other kinematic variables. A tridimensional dynamic rigid body model was used to compute L5/S1 resultant moments. Results showed that the accelerated condition did not reduce body asymmetry of posture, but it reduced the length of the path of the global center of gravity and the duration of the supporting phase of the box, and it did not significantly affect L5/S1 maximal resultant moments for lifting but increased them for lowering. These results indicate that the net work production for accelerated strategies might be smaller, which may represent an economy of energy. Furthermore, the results showed that the use of an accelerated strategy for lowering should be avoided.

acceleration↗
PubMed1987

Determination of lifting abilities: a comparative study of four techniques.

The main objective of this study was to test the differences among four techniques for the determination of lifting abilities. This study introduced a new submaximal isometric strength testing technique. The proposed test was based on the concept of acceptable maximum effort (AME) which is the level of static exertion the individual is willing to perform voluntarily and comfortably without over-exertion (as opposed to the maximum ability of performance). Twelve male and five female subjects underwent the protocol of the four strength testing techniques investigated: isometric maximum voluntary contraction (MVC); maximum acceptable weight (MAW); maximum dynamic lifting (MDL); and acceptable maximum effort (AME). The results showed that MAW recorded the lowest values followed by AME, then MDL, then MVC. The correlation between AME and MAW was higher than that found between MVC and MAW. Also, it was found that AME is a reproducible measure of muscular functional abilities. On the average, the coefficient of variation was less than 15% for data for both males and females. The implications of these results in determining lifting abilities are discussed.

Adult↗
PubMedDate not supplied

The proportional work of lifting the center of mass during walking.

The present study determined the proportion of energy consumption used to lift the center of mass vertically during walking. By assuming that the vertical oscillations of the trunk were identical to those of the center of mass, the complexity of studying the human gait was simplified. The work performed on the center of mass, defined as lift work, was calculated using the subject's mass and the vertical displacement of the trunk. Compensating for the fact that human muscles are approximately 25% efficient in performing external work, the mechanical work was compared with the total energy expenditure, determined using an expired air analysis. At 1.34 and 1.79 m/s, 53.2 +/- 9.3% and 62.8 +/- 8.6%, respectively, of the total energy can be explained by lift work. At 0.45 and 0.90 m/s, the proportions are considerably less, 21.6 +/- 6.6% and 37.6 +/- 8.2%, respectively. These findings provide a rationale for why the metabolic energy cost per unit distance is greater at slower speeds than comfortable or fast speeds of walking. The total energy consumption can be accounted for by changes in the potential and kinetic energies and internal muscular work, defined as the less readily observable work probably needed for balance. The present study demonstrated that the metabolic energy cost of changing the potential energy of the center of mass during walking is significantly less relative to the total energy consumption at slower speeds than at higher speeds. Because kinetic energy is proportional to the square of the velocity, the metabolic energy cost of changing this energy is relatively small at slower speeds. Internal muscular work must therefore play a large role in total energy consumption at slow speeds of walking.

Adult↗
PubMedDate not supplied

Intraabdominal pressure rise during weight lifting as an objective measure of low-back pain.

Twenty-three male patients who had chronic nonspecific low-back pain were asked to record the amount of pain they felt on an arbitrary scale while lifting light weights in different directions. During the lifts their intraabdominal pressures were recorded with an intragastric transducer. The patients who experienced extra pain during the lift had higher rises of pressure than both normal controls and those patients who did not experience extra pain. The available evidence suggests that this pressure rise may be a response to low-back pain and may be used as a method of objectively measuring that pain.

Abdominal Muscles↗
PubMed1987

The loads on the lumbar spine during extreme weight lifting.

The load on the lumbar spine was calculated in eight power lifters when they executed an extremely heavy lift. The calculated load on L3 as well as the total load lifted during training in the last year were related to the bone mineral content (BMC) in the L3 as determined with dual photon absorptiometry. The loads on L3 in the lifters ranged between 18.8 and 36.4 kN. The BMC values were extremely high and closely correlated to the amount of weight lifted during training (r2 = 0.82). The study showed that intensive training will increase the BMC to an extent that the spine can tolerate extraordinary loads.

Adult↗
PubMed2000

Transverse-contour modeling of trunk muscle-distributed forces and spinal loads during lifting and twisting.

STUDY DESIGN: An electromyography-assisted biomechanical model was developed using electromyographic (surface and in-dwelling) data collected during asymmetric lifting and twisting activities. OBJECTIVES: To develop a biomechanical model of the lumbar region that considers the ability of the broad, flat muscles of the trunk (external obliques, internal obliques and latissimus dorsi) to activate different anatomic regions at different intensity levels and then uses this information to describe the spine reaction forces that result during lifting and twisting tasks. SUMMARY OF BACKGROUND DATA: Many biomechanical models of the lumbar region use single-vector representations for the external oblique, internal oblique, and latissimus dorsi muscles. This simplification limits the description of the complexity of the resultant forces produced by these muscles and does not consider their differential activation capacity. METHODS: Human subjects performed lifting and twisting exertions while muscle electromyographic activities were sampled at one location on the rectus abdominis and erector spinae muscles and at multiple locations on the latissimus dorsi, external oblique, and internal oblique muscles. These data were used in conjunction with in vivo digitized muscle origin and insertion points to predict muscle forces and spine loads through the use of the electromyography-assisted modeling method. RESULTS: The measures of model performance such as percentage of error (6-21%) in the prediction of the external torques, correlations (0.83-0.98) between internal and external torques and the values of predicted muscle force capacity were all similar to data collected in previous electromyography-assisted models, but the predictions of spinal loading, particularly shear forces, were quite different. The results have shown that by modeling the broad, flat muscles of the torso using multiple-force vectors, the calculated shear forces in the spine were reduced. CONCLUSIONS: The multivector, transverse-contour model developed in this research illustrates the importance of realistic multiple-vector modeling and the importance of considering the selective-activation capacity of the abdominal oblique musculature.

Abdominal Muscles↗