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PubMed1991

Psychophysical lifting capacity over extended periods.

The effect of time on an individual's lifting capacity over extended periods using a psychophysical approach was studied. Twelve male subjects estimated their lifting capacity in a 25 min period, and then attempted to lift this weight for an 8 h period under varying conditions. For one experimental condition the subjects were allowed to adjust the weight, the final adjusted maximum acceptable weight of lift (MAWOL) averaged 85.4% of the original MAWOL determined in the 25 min session. The subjects also attempted to lift for an 8 h period, without any weight adjustments. All 12 subjects lasted the 8 h at 2 lifts per min, but at a frequency of 8 lifts per min only three subjects completed the eight hour lifting task. This indicates that the psychophysical approach is a valid method to measure lifting capacity across the lower lifting frequency range but overestimates the lifting capacity at the higher frequency range. Slight fluctuations were noted in heart rate and oxygen consumption which were recorded every hour.

Adult↗
PubMed1987

Biomechanical analysis of manual lifting tasks.

This paper presents the findings of a study conducted to determine peak forces generated in the human spine while the individual is engaged in lifting maximum acceptable weight. Calculations of forces and moments, acting on each body segment, were based on film data collected on four individuals for twelve variations of the manual lifting task. The variations were defined by: box-size (three different boxes were used), presence or absence of handles, and symmetry and asymmetry of the lifting task (sagittal and nonsagittal lifting). In general, lower loads were accepted for lift when lifting asymmetrically or when lifting boxes without handles or when lifting bigger boxes. However, peak forces (compressive and shear forces in the spine and ground reaction forces) for these situations were not always lower than those generated when handling either compact boxes or boxes with handles or when lifting boxes symmetrically in the sagittal plane. On the basis of these results, it was concluded that lifting loads asymmetrically or in boxes without handles or in bulky boxes is relatively much more stressful than lifting the same load symmetrically or in boxes with handles or in compact boxes.

Adult↗
PubMed2001

The effects of back belts and load on selected lifting kinematics during a simulated patient transfer.

This study used two dimensional biomechanical analysis to examine the effects of back belts and lifting load on selected lifting kinematics during a simulated patient transfer. A human manikin placed in a sitting position was attached to a customized lifting apparatus which controlled the lifting load and direction of the manikin. Eighteen female participants, between the age of 21 and 27, completed six lifts (sit to stand transfers) of the manikin. Three lifts were completed at the 30 lb load condition (no belt, belt 1 and belt 2) and three lifts were completed at the 50 lb load condition (no belt, belt 1 and belt 2). A doubly two way ANOVA found a significant main effect for the belt condition, F(12,6)=10.06, P=0.002. There was no significant effect for load and no interaction existed between belt and load. The results revealed a significant decrease in trunk flexion when participants wore the wider (nine inch) belt during the 30~lb lifts when compared to the no belt trials. No significant differences were found in trunk flexion means with the narrower width (six inch) belt. No significant differences were found in trunk spinal flexion with either belt condition during the 50 lb lifts. There were no significant differences found in either of the belts in the means of lifting time, knee flexion, elbow flexion, forward displacement of the lifter's center of mass, and the lifter's maximum center of mass velocity. The results suggest that wider back belts may be more effective at reducing spinal flexion during patient lifting under moderate load conditions when compared to narrower back belts and to no-belted controls.

Journal Article↗
PubMed2005

Effects of shoe lift on weight bearing in stroke patients.

OBJECTIVES: To determine the effect of shoe lift, cueing and cueing with shoe lift on weight bearing in paretic leg of stroke hemiparetic patients and compare the effect between each condition. DESIGN: Cross-sectional experimental study. SETTING: Department of Rehabilitation Medicine and Department of Ear Nose and Throat, Faculty of Medicine, King Chulalongkorn Memorial Hospital, Chulalongkorn University. SUBJECT: Ten hemiparetic patients as a result of unilateral stroke. MATERIAL AND METHOD: Weight symmetry of each patient was measured by posturography during quiet stance and in conditions of compelled weight shift. Each patient was started with quiet standing, standing with shoe lift under the sound leg; cueing and cueing with shoe lift under the sound leg respectively. Weight symmetry scores were recorded for comparing the weight distribution between each foot. RESULTS: There were 10 hemiparetic patients. Seven were male. The average age was 53.4 +/- 8.45 years. There were 5 right hemiparesis and 5 left hemiparesis. The average onset was 12.3 +/- 15.73 months. In the right hemiparetic patients, weight bearing in the paretic leg was significantly improved when cueing with shoe lift compared with quiet standing and with shoe lift (Backward p = 0.012, Forward p = 0.011 and Backward p = 0.001, Forward p = 0.036 respectively). In the left hemiparetic patients, weight bearing in the paretic leg was significantly improved when cueing compared with quiet standing (Backward p = 0.046), and when using the shoe lift (Backward p = 0.016). Cueing with shoe lift could significantly improve weight bearing in the paretic leg when compared with shoe lift alone (Backward p = 0.015). Shoe lift alone could improve weight bearing in the paretic leg of the right and left hemiparetic patients but was not statistically significant (p > 0.05). CONCLUSION: Cueing with shoe lift under the sound leg can significantly improve weight bearing of the paretic leg of the right and left stroke hemiparetic patients.

Cross-Sectional Studies↗
PubMed1988

Maximal aerobic capacity for repetitive lifting: comparison with three standard exercise testing modes.

A multi-stage, repetitive lifting maximal oxygen uptake (VO2max) test was developed to be used as an occupational research tool which would parallel standard ergometric VO2max testing procedures. The repetitive lifting VO2max test was administered to 18 men using an automatic repetitive lifting device. An intraclass reliability coefficient of 0.91 was obtained with data from repeated tests on seven subjects. Repetitive lifting VO2max test responses were compared to those for treadmill, cycle ergometer and arm crank ergometer. The mean +/- SD repetitive lifting VO2max of 3.20 +/- 0.42 l.min-1 was significantly (p less than 0.01) less than treadmill VO2max (delta = 0.92 l.min-1) and cycle ergometer VO2max (delta = 0.43 l.min-1) and significantly greater than arm crank ergometer VO2max (delta = 0.63 l.min-1). The correlation between repetitive lifting oxygen uptake and power output was r = 0.65. VO2max correlated highly among exercise modes, but maximum power output did not. The efficiency of repetitive lifting exercise was significantly greater than that for arm cranking and less than that for leg cycling. The repetitive lifting VO2max test has an important advantage over treadmill or cycle ergometer tests in the determination of relative repetitive lifting intensities. The individual curves of VO2 vs. power output established during the multi-stage lifting VO2max test can be used to accurately select work loads required to elicit given percentages of maximal oxygen uptake.

Adult↗
PubMed2006

Manual materials handling in mining: the effect of rod heights and foot positions when lifting "in-the-hole" drill rods.

There is a paucity of studies focusing on the lifting of rods or long awkward heavy objects. In-the-hole (ITH) drilling is a heavy repetitive mining task, which has been identified as having a relatively high incidence and severity rate of musculoskeletal injuries. The purpose of this study was to examine how the load experienced by ITH drill operators changed when lifting a vertical drilling rod (1.61m, 35kg) using two rod heights and four different foot positions. In addition, a symmetrical lift with a lifting index (LI) of 1.4 also served as a comparison to determine possible risk of low back injury. Eleven experienced ITH drill operators participated in the study. Each subject was required to lift a vertical drilling rod until the upper body was in an erect posture using four different foot positions (0 degrees =subject facing the rod, 45 degrees =subject oblique to the rod, 90 degrees =subject right side to the rod and freestyle). In addition, two rod height conditions were studied where the base of the vertical rod was supported either (1) at ground level (height of rod CG=0.83m) or (2) on a 20cm rack (height of rod CG=1.03m). Finally, each subject lifted a 21.5kg box in the sagittal plane, which corresponded to an LI of 1.4 in the NIOSH lifting equation. Reflective markers were placed on the subjects, and three video cameras and one force plate were used to record the forces and the motion of the subjects' segments. Two surface electrodes were applied on the right and the left erector spinae (ES) at the level of L3. Back loading was defined by the level of the peak moments, the mechanical work and erector spinae muscle activity (EMG). It was found that the vertical height of the rod had the most significant impact on back loading, while the effect of the initial foot positioning relative to the rod was limited by the technique adopted by the drillers. Moreover, it was found that some of the subjects used techniques less strenuous for the back than others. Finally, the asymmetrical lifting component was found to be the most negative aspect of lifting an ITH drill rod compared to a standard symmetrical lift (NIOSH).

Accidents, Occupational↗
PubMed2003

Isokinetic and isometric lifting capacity of Chinese in relation to the physical demand of job.

The aim of the study was to formulate normative data for the lifting capacities of a normal Chinese population, in order to establish a basic foundation for further studies and to investigate the relationship between individual attributes including age, gender, height, weight, job physical demand and each type of lifting capacity. Isokinetic and isometric lifting strength at low, waist and shoulder assessment levels were measured using the LIDO Workset II based on a sample of 93 normal Chinese adults (63 men and 30 women) between the ages of 21-51. The 50th percentile score for adult Chinese female's lifting strength was 17.71% lower than the American female while the adult Chinese male's lifting strength was 14.94% lower than the American male. Lifting forces were higher in the 20-40 year age group. The isometric work mode had considerable impact on the lifting capacities, with shoulder level having the highest lifting capacities. The gender and body weight had a significant positive correlation to lifting capacity while job physical demand had a moderate correlation. Age and body heights were weakly correlated to lifting capacity.

Adult↗
PubMedDate not supplied

Spine loading in patients with low back pain during asymmetric lifting exertions.

BACKGROUND CONTEXT: Recurrent low back pain (LBP) is a common and costly problem that might be related to increased spine loads in those with LBP. However, we know little about how the spine is loaded when those with LBP perform lifting exertions. PURPOSE: Document spine loading patterns of patients with LBP performing symmetric and asymmetric lifting exertions compared with asymptomatic individuals performing the same tasks. STUDY DESIGN: Spine loadings during lifting exertions that varied in asymmetric origin as well as horizontal and vertical distance from the spine were compared between asymptomatic subjects and patients with LBP. METHODS: Sixty-two patients with LBP and 61 asymptomatic individuals performed a variety of lifting exertions that varied in lift origin horizontal and vertical position (region), lift asymmetry position and weight lifted. An electromyography-assisted model was used to evaluate spine loading in each subject during the lifting exertions. Differences in spine loading between the LBP and asymptomatic subjects were noted as a function of the experimental variables. RESULTS: Patients with LBP experienced greater spine compression and shear forces when performing lifting tasks compared with asymptomatic individuals. The least taxing conditions resulted in some of the greatest differences between LBP and asymptomatic individuals. CONCLUSIONS: Greater levels of antagonistic muscle coactivation resulted in increases in spine loading for patients with LBP. Specific lifting conditions that tend to exacerbate loading can be identified by means of physical workplace requirements. These findings may impact acceptable return-to-work conditions for those with LBP.

Adult↗
PubMed2000

Effects of box weight, vertical location and symmetry on lifting capacities and ratings on category scale in Japanese female workers.

The aim was to clarify the effects of box weight, vertical location and symmetry on the lifting capacities and subjective burden in Japanese female workers with manual material handling tasks. Sixteen healthy females were tested. They performed 12 different lifting tasks (three heights * two weights * two symmetries). It is difficult for Japanese women to exert dynamic force in lifting a 15-kg weight from the elbow to the shoulder level. A remarkable increase was observed in heart rate and category scale with ratio properties (CR-10) on large muscle group in lifting a 15-kg weight as compared with lifting a 10-kg one. Judging from calculation of the Recommended Weight Limit using the application manual by the National Institute for Occupational Safe and Health, it was also suggested that lifting the 15-kg weight from the elbow to the shoulder level was difficult for female workers. Not only peak force, but also the average upward acceleration and peak velocity were lower in asymmetric liftings than those in symmetric liftings. CR-10 for the left back and right thigh were also higher in 90 degrees right lateral plane lifting than in the mid-sagittal plane. Thus, asymmetric lifting was supposed to impose higher stress on the back contralaterally and thigh ipsilaterally to the location of the weight.

Adult↗
PubMed1995

Comparative analysis of the workload in seated and standing horizontal submaximal lifting tasks.

The objective of the present laboratory study was to analyse physiological responses of horizontal lifting tasks when they were performed in sitting and standing positions. Heart rate and blood pressure were used as indices of circulatory strain. Lifting tasks were performed under four lifting positions: sitting-forward lift, sitting-twist lift, standing-forward lift, and standing-twist lift. The weights of the loads were 3, 5 and 7 kg and the frequencies of handling were 1, 4 and 6 lifts/min. This study supports the idea that heart rate is a sensitive measure for evaluating the effects of seated horizontal lifting tasks. The lifting positions and workload (frequency x load x distance) are important parameters in the design of these types of tasks. It appears that within the experimental values examined in this study, a seated position could be recommended while performing horizontal lifting tasks at workloads < or = to 4.6 kg.m.min-1. The results are supported by smaller physiological responses.

Adult↗
PubMed1995

Neuromuscular coordination of squat lifting, II: Individual differences.

BACKGROUND AND PURPOSE: This article reports individual differences in the coordination (ie, the relative timing of joint movements and muscle activity) of squat lifting identified by extended analysis of data reported in the authors' companion article in this issue. SUBJECTS: Two post hoc groups of 6 subjects each were identified from the original sample of 15 subjects based on qualitative differences in knee-lumbar spine relative motion plots during load acceleration. METHODS: Subjects lifted a crate containing 15% to 75% of their maximum lifting capacity using a symmetrical squat-lift technique. Movement kinematic data were obtained with videography, and the electromyographic (EMG) activity of the vastus lateralis and erector spinae muscles was recorded with surface EMG. Measurements of coordination derived both kinematically and via EMG and the kinematic data were examined for group differences. RESULTS: Subjects in group 2 limited lumbar spine motion during load acceleration for all loads lifted, whereas those in group 1 limited lumbar spine motion more when lifting the heaviest loads. These differences were obvious both qualitatively, via knee-lumbar spine relative motion plots, and quantitatively, via measures of the relative timing of joint motions early in the lift. The effect of load on the coordination of these joints was the same for both post hoc groups after initial load acceleration. Significant differences in other kinematic measurements were also found between these groups. CONCLUSION AND DISCUSSION: Despite specific instructions about how to lift the load, individual subjects coordinated their joints differently during the initial, accelerative phase of squat lifting. Individual differences in coordination in response to load increases could be categorized into two patterns, although the data of 2 subjects were difficult to categorize and thus not included in these analyses. Whether the two dominant patterns have consequences for stress to the joints during lifting remains to be determined.

Acceleration↗
PubMed1992

Myoelectric activity and sequencing of selected trunk muscles during isokinetic lifting.

Trained weight lifters lift heavy loads without a concomitant degree of acute low-back injuries. To study the process by which large loads are lifted with minimal injury, integrated electromyographic signals were recorded from four large muscle groups: gluteus maximus, quadriceps, latissimus dorsi, and erector spinae in 4 weight lifters and 11 asymptomatic control subjects. These signals were recorded during a floor-to-knuckle-height isokinetic lift (dead lift) at 30.5 and 45.7 cm/sec. The signals were normalized for the height of the lift and the maximal isokinetic integrated electromyographic activity. The weight lifters achieved maximal force at 50% of maximal lift height, whereas the control subjects achieved it at 67%. Although not statistically significant, the weight lifters used the gluteus maximus more during the early stages of the lift, perhaps contributing to earlier development of force. This process would stabilize the pelvis and permit the erector spinae to extend the trunk more efficiently. The weight lifter then completed the lift with prolonged and increasing activity in the quadriceps. This technique may minimize the required force in the erector spinae and the forces on the low-back structures. Clinical implications include more effective strength training of lifting muscle groups other than spinal extensors and the teaching of lifting strategies employed by weight lifters in low-back rehabilitation and work-hardening programs.

Back↗
PubMed1994

Ratings of perceived thigh and back exertion in forest workers during repetitive lifting using squat and stoop techniques.

STUDY DESIGN: Local thigh and low back perceived exertion (RPE), sagittal peak load moments, and leg and trunk muscular activity during repetitive submaximal lifting, with squat and stoop technique, were investigated. OBJECTIVES: This study analyzed changes in kinetic variables caused by changes in body movements during the lifting bouts, and the contribution of the biomechanical and physiologic variables to the variability in the local RPE responses. SUMMARY OF BACKGROUND DATA: Despite instructions that emphasize the "correct" lifting technique as the squat technique, the stoop technique is reported as more commonly used in practice. Few studies have investigated the effect of lifting technique on differentiated perceptual responses in repetitive lifting. METHODS: Ten experienced forest workers performed submaximal repetitive lifting bouts until steady-state VO2 was reached, using five different weight and frequency combinations with both squat and stoop techniques. Borg's scale was used for RPE measurements. Muscular activity in lumbar, hip, knee extensors, and knee flexors was recorded with surface electrodes. Kinematic data was obtained from electronic liquid-level sensors, and vertical ground reaction forces from a two-dimensional force plate. RESULTS: Low back RPE was higher for stoop than for squat, whereas the opposite was true for thigh RPE. The total accountable variance (R2) for the biomechanical and physiologic variables to the RPE responses ranged from 0.25 (low back RPE in squat lifting) to 0.61-0.76 for the other assessments. During the time course in squat lifting at the highest frequency, the knee load moment decreased and the vertical ground reaction forces increased. CONCLUSIONS: The study indicates that "movement strategies" to reduce the demand on the knee-extensor muscles were used during the squat lifting bouts at the highest frequencies, which combined with the relatively high assessed thigh exertions, leads to the hypothesis that quadriceps muscle exertion is the "weak link" for the squat technique. The study also indicates a discrepancy between the measured and perceived low back stress in squat repetitive lifting.

Adult↗
PubMed2001

Lifting strategy and stability in strength-impaired elders.

STUDY DESIGN: Ninety-six subjects underwent biomechanical analysis of freestyle box lifting. OBJECTIVES: To relate lifting strategy to lower extremity muscle strength and postural stability in functionally limited elders. SUMMARY OF BACKGROUND DATA: Back pain and postural instability in elders is rampant and poorly understood. Much of the literature on lifting relates to young subjects. METHODS: Lifting strategy for 91 functionally limited elders was classified by timing of peak power in the back and knee joints. Isometric hip and knee extensor strength and postural stability were compared among strategy classifications. Postural stability was analyzed by measuring center of gravity (CG) displacement during lifting. RESULTS: Three lift strategy groups were established: back-lift, or back dominant strategy (BDS); leg-lift, or leg dominant strategy (LDS); and leg-dominant back-first mixed strategy (LDB). Subjects with relatively strong hip and knee extensors used leg dominant strategy; subjects with relatively strong knee, but weak hip, extensors used leg-dominant back-first mixed strategy; and subjects with weak hip and knee extensors used back dominant strategy. Leg dominant strategy and leg-dominant back-first mixed strategy engendered less center of gravity displacement and thus were posturally more stable than the back dominant strategy. CONCLUSION: Subjects apparently chose their lift strategy based on their hip and knee extensor strength. Weaker elders using a less stable back dominant strategy could be susceptible to falls and subsequent long bone and vertebral body fractures. Clinicians could identify at-risk elders by muscle testing. Beyond emphasizing strength and endurance exercise in elderly patients, weak elders should be taught to use a leg dominant lifting strategy, or if they are not physically able, to use a combined back/leg strategy.

Aged↗
PubMed2001

The effect of wearing a back belt on spine kinematics during asymmetric lifting of large and small boxes.

STUDY DESIGN: A crossover design was used to evaluate kinematic measurements collected with an infrared-based motion measurement system. OBJECTIVES: To evaluate belt effects on spine kinematics during asymmetric lifting of large and small boxes and to test for carryover effects between trials from belts. SUMMARY OF BACKGROUND DATA: Conflicting evidence in the literature exists regarding whether belts are beneficial or detrimental to manual material handlers. Studies have not examined belt effects when lifting different sized boxes, nor carryover effects from belts. METHODS: Twenty-eight subjects with manual-handling experience (17 male and 11 female) were randomly assigned to lift either a large or small box (weighing 9.4 kg), from a sagittally symmetric origin at pallet height to a 79 cm height, 60 degrees to the right. Spine flexion, lateral bending and twisting, hip and knee flexion, and angular velocity measurements of the torso with respect to the pelvis were collected for each of three lifting periods, 50 lifts each at 3 lifts per minute, with 18-minute breaks between periods. RESULTS: Belts significantly reduced maximum spine flexion, spine flexion and extension angular velocities, and torso left lateral bending angular velocity, and increased hip and knee flexion, regardless of box size. When lifting large boxes, belts significantly reduced torso right lateral bending and torso left twisting. No significant differential carryover effects were detected from belts. CONCLUSIONS: Subjects with belts lifted more slowly and used more of a squat-lift technique, regardless of box size. Belts reduced more torso motions while lifting large boxes.

Adolescent↗
PubMed1997

Effects of team size on the maximum weight bar lifting strength of military personnel.

Teamwork is an essential element in the majority of critical Army lifting tasks. Therefore, an understanding of the relationship between individual and team lifting capacity is of great tactical importance. Twenty-three male and 17 female U.S. Army soldiers were randomly assigned to single- and mixed-gender teams of two, three, and four persons. Individual lifting strength was the one-repetition-maximum (1RM) load lifted from floor to knuckle height using a weight bar. A square-shaped bar was used for two- and four-person lifting, and a triangular-shaped bar was used for three-person lifting. Team lifting strength as a percentage of the sum of individual lifting strength (%sum) did not change with team size. The %sum for teams of men (87.3%) was less than for teams of women (91.1%, p < 0.05). The %sums for both single-gender teams (all men and all women) were greater (p < 0.01) than for mixed-gender teams (80.2%). The number of people lifting a large object was increased to four with no decrease in the effectiveness of the individual lifter beyond that found for two persons. The 1RM loads presented in this paper were lifted under ideal conditions by young soldiers and do not represent norms for an industrial population.

Cooperative Behavior↗
PubMed2001

[Workload, gender and age among personnel with reported sudden lifting injuries].

INTRODUCTION: In 1996 the Danish Parliament passed a new Act on industrial injuries, including the so-called sudden lifting injuries. This type of lifting injury had been experienced in some industries in connection with lifting situations causing sudden pain in the back. Less frequently, other regions of the body may be affected. This study is a distribution of a sample of reported industrial injuries of this type in groups according to types of lifts. The study also includes a comparison with parameters from the Danish Work Environment Cohort Study. MATERIAL AND METHODS: The sample consisted of a total of 482 cases of back injuries. Of these, 346 cases were distributed according to six categories of manual lifting work and to age and gender. The rest, 136 cases, were excluded for technical reasons. RESULTS: In the distribution, 8% of the cases were in jobs with many heavy lifts, 66% of the cases were in jobs with moderate daily lifted weights or in jobs with only few or light lifts. Approximately 25% of cases concerned employees performing patient transfers. The distribution contained more men than the Danish Work Environment Cohort Study, and the persons in the cases were slightly older than this reference population. DISCUSSION: Altogether, this study points towards an occurrence of sudden lifting injuries among employees performing certain types of manual lifting work. The industrial injuries cases may have been subject to some selection.

Accidents, Occupational↗
PubMed2003

Lifting teams in health care facilities: a literature review.

1. Manual lifting and transfer activities are job tasks frequently associated with back injuries in nursing personnel. One approach with potential to decrease these injuries is the lifting team. 2. In program evaluations completed to date, there have been numerous benefits and several limitations attributed to use of lifting teams in health care facilities. 3. Benefits of lifting teams include reductions in lost time workdays, restricted workdays, workers' compensation claims, and injuries to lifting team members; satisfaction of patients, staff, and lifting team members; and capacity of the lifting team to absorb the majority of high risk lifts and transfers on shifts in which they operate. 4. Lifting teams may not be appropriate for all settings, require infrastructure and lifting team equipment to support their use, and require careful consideration related to staffing. However, when their use is appropriate, efforts to overcome their limitations can be accomplished with careful evaluation of outcome measures and indicators.

Accidents, Occupational↗