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PubMed2002

Spinal loading when lifting from industrial storage bins.

The study documented three-dimensional spinal loading during lifting from an industrial bin. Two lifting styles and two bin design factors were examined in Phase I. The lifting style measures in Phase I were one hand versus two hand and standing on one foot versus two feet. The bin design variables were region of load in the bin and bin height. The Phase II study examined one-handed lifting styles with and without supporting body weight with the free hand on the bin as well as region and the number of feet. Twelve male and 12 female subjects lifted an 11.3 kg box from the bin. Spinal compression, lateral shear and anterior - posterior shear forces were estimated using a validated EMG-assisted biomechanical model. Phase I results indicated that the bin design factor of region had the greatest impact on spinal loading. The upper front region minimized spinal loading for all lifting styles. Furthermore, the lifting style of two hands and two feet minimized spinal loading. However, comparing Phase I two-handed lifting with Phase II one-handed supported lifting, the one-handed supported lifting techniques had lower compressive and anterior - posterior shear loads in the lower regions as well as the upper back region of the bin. A bin design that facilitates lifting from the upper front region of the bin reduces spinal loading more effectively than specific lifting styles. Furthermore, a bin design with a hand hold may facilitate workers using a supported lifting style that reduces spinal loading.

Adult↗
PubMed1998

Spine loading during asymmetric lifting using one versus two hands.

This study documented three-dimensional spinal loading associated with asymmetric lifting while using either one or two hands to perform the task. Lift asymmetry was defined as a function of the load origin relative to the sagittal plane of the body. Lifts occurred at 0, 30, or 60 degrees off the sagittal plane on both sides of the body (lifting from the right and from the left relative to the sagittal plane). Ten subjects lifted a 13.7 kg box from one of these origins to a sagittally symmetric destination. Spinal loads were estimated through the use of a validated EMG-assisted model. Spine compression and lateral shear forces increased as the lift origin became more asymmetric. However, spinal compression and lateral shear increased by about twice the rate when lifting from origins to the left of the sagittal plane compared to lifting from origins to the right of the sagittal plane. Anterior-posterior spinal shear decreased as asymmetry increased with larger decreases occurring when lift origins occurred to the right of the sagittal plane. One-hand lifting changed the compression and shear profiles significantly. One-hand lifts using the hand on the same side of the body as the load resulted in compression forces that were approximately equal to those observed when lifting with two hands in a sagittally symmetric position. Anterior-posterior shear decreased and lateral shear increased under these conditions. These results reflect the trade-offs that must be considered among spinal forces during asymmetric lifting while using one or two hands. These findings have significant implications for task assessment interpretation and workplace design.

Adult↗
PubMed1992

Erector spinae activation and movement dynamics about the lumbar spine in lordotic and kyphotic squat-lifting.

Activation of the erector spinae during squat lifts depends on the initial posture of the lumbar spine. The authors assessed erector spinae activation by electromyography during squat lifts from lordotic and kyphotic postures, measured kinematics of the lifts from digitized video images, and inferred torques from the kinematics, using a two-dimensional model of a human lifting in the sagittal plane, with a joint at L3. Lifts from the lordotic initial posture had peak electromyographic signals early in the lift, whereas lifts from kyphotic initial posture had an initial "flexor relaxation," and peak activity in the middle of the lift. Lumbar flexion was much greater in lifts from kyphotic initial position. Torques required about L3 were similar between the two postures, though somewhat larger initially in lifts from kyphosis. The largest torques were therefore sustained by flexed lumbar spines, during periods of little or no erector spinae activity, in lifts made from kyphotic initial position. A sizable portion of the early torque is inertial, and therefore strongly dependent on movement time. Movements with a 30-lb load in the hands were similar, in kinematics and electromyography, to unloaded lifts, though longer in duration. The clinical implications of the differences in activation with posture, the practical implications of the inertial component of torque, and the need for consideration of lumbar posture in future modeling of squat lifting are discussed.

Adult↗
PubMed1996

The effects of lumbosacral support belts and abdominal muscle strength on functional lifting ability in healthy women.

STUDY DESIGN: This study focused on lumbosacral support belts, abdominal muscle strength, and lifting ability in healthy women. Subjects underwent manual muscle testing to determine muscle strength and performed lifting procedures to determine lifting capacity. OBJECTIVES: The purpose of this study is threefold: 1) to determine the effectiveness of lumbosacral support belts in improving lifting ability in healthy women, 2) to determine if lumbosacral support belts are more effective for those with weak abdominals than those with strong abdominals, and 3) to determine if the maximum amount of weight varies with abdominal muscle strength. SUMMARY OF BACKGROUND DATA: In a review of published literature, one study has addressed the relationship of lumbosacral support belts and lifting capacity. However, no study has examined the use of lumbosacral support belts and lifting capacity in a female population. METHODS: A convenient sample of 69 healthy women, aged 20 to 40 years, participated in this study. Subjects were categorized into one of three groups based on lower and upper abdominal muscle strength. Each subject then performed two lifting procedures, one with a lumbosacral support belt and one without, to determine two maximum lifts. RESULTS: Women between the ages of 20 and 40 years could lift approximately 1.0 kg more weight from the floor to waist height with the lumbosacral support belt. The maximum weight lifted varied with abdominal strength. Lumbosacral support belts were not more effective for those with weak abdominals than those with strong abdominals. CONCLUSIONS: When applied properly and used in conjunction with proper lifting technique, lumbosacral support belts slightly improved lifting ability in healthy women. The magnitude of the increase, although statistically significant, is not sufficient to advocate the use of lumbosacral support belts to increase lifting capacity.

Abdominal Muscles↗
PubMed2003

Muscle fatigue and fatigue-related biomechanical changes during a cyclic lifting task.

STUDY DESIGN: Electromyographic and biomechanical methods were utilized to investigate correlations between indexes of localized muscle fatigue and changes in the kinematics and kinetics of motion during a cyclic lifting task. SUMMARY OF BACKGROUND DATA: Recent advances in time-frequency analysis procedures for electromyographicic signal processing provide a new way of studying localized muscle fatigue during dynamic contractions. These methods provide a means to investigate fatigue-related functional impairments in patients with low back pain. OBJECTIVES: To study the relationship between localized muscle fatigue and the biomechanics of lifting and lowering a weighted box. Fatigue-related changes in the electromyographicic signal of trunk and limb muscles were evaluated and compared to kinematic and kinetic measures in order to determine whether lifting strategy is modified with fatigue. METHODS: A total of 14 healthy male subjects (26 +/- 5 years) cyclically lifted and lowered a 13 kg box (12 lifts/min) for 4.5 minutes. A 5-second static maximum lifting task was included immediately before and after the cyclic lifting task to measure changes in lifting strength and static electromyographicic fatigue indexes. Electromyographic signals from 14 muscle sites (including paravertebral and limb muscles) were measured. Changes in the electromyographicic Instantaneous Median Frequency, a fatigue index, were computed using time-frequency analysis methods. This index was compared with more standardized measures of fatigue, such as those based on electromyographicic median frequency acquired during a static trunk extension test, subjective fatigue measures, and maximal static lifting strength. Biomechanical measures were gathered using a motion analysis system to study kinematic and kinetic changes during the lifting task. RESULTS: During the cyclic lifting task, the electromyographic Instantaneous Median Frequency significantly decreased over time in the paravertebral muscles, but not in the limb muscles. Paravertebral electromyographicic Instantaneous Median Frequency changes were consistent with self-reports of fatigue as well as decreases in trunk extension strength. The magnitude of muscle-specific changes in electromyographicic Instantaneous Median Frequency was not significantly correlated with electromyographicic median frequency changes from the static trunk extension task. The load of the box relative to the maximal static lifting strength significantly affected the electromyographicic Instantaneous Median Frequency changes of paravertebral back muscles. Significant changes with fatigue during the task were found in the angular displacements at the knee, hip, trunk, and elbow. These biomechanical changes were associated with increased peak torque and forces at the L4-L5 vertebral segment. CONCLUSIONS: Our results demonstrate correlation between localized muscle fatigue and biomechanical adaptations that occur during a cyclic lifting task. This new technique may provide researchers and clinicians with a means to investigate fatigue-related effects of repetitive work tasks or assessment procedures that might be useful in improving education, lifting ergonomy, and back school programs. Although both the dynamic and static tasks resulted in spectral shifts in the electromyographicic data, the fact that these methods led to different muscle-specific findings indicates that they should not be considered as equivalent assessment procedures.

Adult↗
PubMedDate not supplied

Lifting characteristics of functionally limited elders.

BACKGROUND: The purpose of this study was to investigate the lifting characteristics of elders with functional limitations using burden lifting smoothness, trunk angular momentum, and back and hip torque, and to correlate these characteristics with strength and functional measures. METHODS: Thirty elders (65-89 years old) consented to biomechanical analysis of lifting, gait, and chair rise, and to maximum isometric strength testing of the hip and knee extensors and shoulder flexors. Jerk, the rate of change of acceleration, is a measure of smoothness of motion. We calculated peak vertical jerk of the box at the beginning part of the lift. Momentum is the product of mass and velocity. HAT (head, arms, trunk) angular momentum was calculated during chair rise. RESULTS: Hip extensor strength correlated positively with box jerk, as did box jerk and peak trunk angular momentum between subjects. There was an inverse correlation between peak upper body angular momentum when lifting a box from floor to knee height, and gait speed normalized to body weight. There was a positive correlation between trunk angular momentum during lifting and trunk angular momentum during chair rise. CONCLUSION: Stronger subjects used more peak vertical box jerk and more trunk peak angular momentum to lift a box from floor to knee height. Stronger subjects who used more HAT angular momentum during free speed chair rise also used more trunk peak angular momentum during the first phase of the lift, but lifting characteristics were independent of gait velocity. Weaker subjects used less peak momentum and peak jerk, choosing instead a more conservative, and apparently more stable, lifting strategy. Before counseling elderly patients on proper body mechanics for lifting, clinicians should assess strength and functional status. Weak elders should be taught a lifting strategy that allows them to maintain optimal balance, and to lift without jerking the load.

Aged↗
PubMed2006

[Evaluation of work load and related factors during asymmetric lifting with surface electromyography].

OBJECTIVE: To evaluate the work load and related factors for asymmetric lifting tasks using surface electromyography (EMG). METHODS: Thirteen male volunteers lifted loads of 6 and 13 kg at two speeds, in varying angles of trunk rotation, from floor to knuckle height, performing 16 lifting tasks. During lifting, surface electromyography signals from the erector spinae, bilaterally at level of T10 and L3, was continually recorded. The work load and related factors for asymmetric lifting tasks were evaluated by comparing the average amplitude of EMG signals. RESULTS: The EMG average amplitude when lifting the load of 13 kg (43.30% MVE) was significantly greater than that when lifting the load of 6 kg (37.70% MVE) (P < 0.01). The EMG average amplitude when lifting at the higher speed (41.80% MVE) was significantly greater than that at the lower speed (39.19% MVE) (P < 0.05). The EMG average amplitude was increased with the increase of the trunk rotation angle without significant difference (P > 0.05). At T10, the EMG average amplitude was greater on the right side than that on the left side (50.31% MVE and 25.88% MVE respectively) while at L3, it was on the contrary (45.60% MVE on the left and 40.22% MVE on the right respectively) (P < 0.01). Multiple stepwise regression analysis showed that the load of lifting was the factor contributing most to the EMG average amplitude followed by the lifting speed. CONCLUSION: The risk factors related to work load for asymmetric lifting tasks are mainly the load and the speed of lifting. The EMG activity between the right and left side of erector spinae is different during such lifting.

Adult↗
PubMed1996

Study of isometric lifting strength in normal Chinese adults.

The purposes of this study were to describe norms of isometric lifting strength for healthy Chinese adults and to investigate the effects of age, gender, body weight, and body height on lifting strength. Three types of lifting (i.e., arm, back, and leg lifting) were measured in a sample of 350 Chinese adults (172 men and 178 women) aged between 20 and 81 years. A Force Evaluation and Testing System (FET 5000) was used for strength measurements with three standard lifting positions. The average of two trials for each lifting strength test was used as the subjects' test score. The results showed that the greatest strengths for both sexes exist aged between late 20's and early 30's, with a general decline following thereafter. The magnitude of strength decline with age was most prominent in leg lifting strength among all lifting patterns. Males were stronger than females in all lifting patterns among the different age groups. All of the lifting strengths studied correlated positively with gender, body weight, and body height, and negatively with age in the analyses of simple correlation coefficients. In addition, stepwise multiple regression analyses showed that sex, age and body weight were most predictive of all types of lifting strengths. Body height was an effective predictor of back lifting strength. These findings and the establishment of data base can provide therapists with an objective evaluation regarding lifting strength of individuals for clinical use.

Adult↗
PubMed1997

Hip stress during lifting with bent and straight knees.

"Correct" body mechanics during lifting are believed to protect the back by employing knee and hip flexion while keeping the back straight. Lower limb joint stress, however, has been largely ignored. We compared hip cartilage contact stress during "leg lifting" with "back lifting" (lifting with bent or straight knees, respectively) in a subject fitted with a pressure instrumented hip endoprosthesis. Synchronized pressure data and whole-body kinematics and kinetics were collected simultaneously while the subject lifted an 11.8 kg mass from the floor to waist level. The highest pressure, 13.7 MPa, occurred during leg lifting at the antero-lateral femoral head transducers opposed at maximum hip flexion by the postero-superior quadrant of acetabular cartilage. In back lifting, the highest pressure, 11.5 MPa occurred in the supero-lateral aspect of the head, which during hip extension was opposed by the posterior quadrant of the acetabulum. Maximum pressures and hip torques occurred simultaneously with peak hip flexion, during the initial lifting of the burden from the floor. Acetabular contact pressures during leg lifting were on average twice as great as during back lifting, and both techniques generate much greater hip stress than gait (typically 4-6 MPa). Degenerative changes in the articular surface of the acetabulum occur primarily on the postero-superior aspect, corresponding to the locations of peak contact pressures in the present in vivo data. Thus leg lifting puts more stress on the postero-superior region, and probably contributes to more hip cartilage degeneration, than does back lifting. We conclude that although leg lifting may mechanically protect the back, it substantially increases hip cartilage stress.

Aged↗
PubMed1998

Three dimensional moments in the lumbar spine during asymmetric lifting.

OBJECTIVE: To better understand the loads placed on the spine during asymmetric lifting. DESIGN: Analysis of variance was used to test the effects of asymmetry (0, 45, 90 degrees ), event (up, down, min and max), and trial (first and second) on applied spine moments and resulting EMG signals in the lumbar spine. BACKGROUND: Loading conditions resulting from symmetric lifting are well documented in the literature, yet free-style asymmetric tasks have not been intensively studied. METHODS: Infrared markers and EMG electrodes were fixed to ten subjects. Subjects were asked to lift a 45 N weight from three different positions in relation to the sagittal plane. External loads on the L3-L4 and L4-L5 disc planes were calculated. Maximum moments and EMG were compared with those at lift off and set down of the burden. All lifts were repeated twice. RESULTS: Introducing asymmetry to the lift increased lateral bending and twisting moments. Flexion moments increased by approximately 5% after lift off of the load. During the second repetition of the lift, flexion and twisting moments decreased and increased, respectively. EMG signals were greater on the contralateral side during asymmetric lifts. CONCLUSIONS: Asymmetric lifting places complex loads across the trunk, which may become increasingly asymmetric with repeated trials. RELEVANCE: Individuals should take precautions to perform lifts in a symmetric manner and to avoid repetitive asymmetric lifting if possible. Past study indicated that twisting and lateral bending loads, when coupled with flexion loads, resulted in much greater disc compression and should be avoided. This work described the degree to which lateral bending and twisting loads were introduced as lifts deviated from the sagittal plane.

Journal Article↗
PubMed1994

Bending and compressive stresses acting on the lumbar spine during lifting activities.

Cadaveric studies have shown that intervertebral discs and ligaments are most vulnerable to injury when loaded simultaneously in bending and compression. The purpose of the present experiment was to measure bending and compressive stresses acting on the lumbar spine during forward bending and lifting activities, and to identify those aspects of lifting which increase the risk of injury. Twenty-one men and eighteen women lifted objects from the ground while the following parameters were varied: the angle of the knees ('squat' lift or 'stoop' lift), the mass of the object, its bulk, its distance in front of the feet, its distance away from the sagittal plane, and the speed of movement. Spinal compression was assessed by measuring the peak extensor moment generated by the back muscles and fascia during the lift. Extensor moment was calculated from the EMG activity of the erector spinae muscles, using corrections for muscle length, contraction velocity and electro-mechanical delay. The bending moment ('bending torque') acting on the intervertebral discs and ligaments was quantified by comparing dynamic measurements of lumbar flexion, obtained with the '3-Space Isotrak', with the normalised bending properties of cadaveric lumbar spines. Results showed that stoop lifting reduced the peak extensor moment by about 10% compared to squat lifting, but increased the bending torque by about 75%. Extensor moment and bending torque both increased substantially with increasing mass, bulk and distance from the feet. Non-sagittal plane lifts increased the bending torque by about 30%. The fastest lifts increased peak extensor moment by 60% but did not increase bending torque. We conclude that complex spinal loading during lifting tasks depends as much on the speed of movement, and the size and position of the object lifted, as on its mass. Analyses of spinal loading which consider only compressive forces do not give a full indication of the risk of injury to the intervertebral discs and ligaments.

Adult↗
PubMed2006

The effects of container size, frequency and extended horizontal reach on maximum acceptable weights of lifting for female industrial workers.

In the development of our present manual materials handling (MMH) guidelines (Snook, S.H., Ciriello, V.M., 1991. The design of manual tasks: revised tables of maximum acceptable weights and forces. Ergonomics 34, 1197-1213), the assumption was made that the effects of frequency on maximum acceptable weights (MAWs) of lifting with a large box (hand distance, 38 cm from chest) were similar to that of lifting with a small box (hand distance, 17 cm from chest). The first purpose of the present experiment was to investigate this assumption with female industrial workers. The second purpose was to study the effects of extended horizontal reach lifting (hand distance, 44.6 cm from chest) on MAWs as a confirmation of the results of a previous studies on this variable with males (Ciriello, V.M., Snook, S.H., Hughes, G.J., 1993. Further studies of psychophysically determined maximum acceptable weights and forces. Hum. Factors 35(1), 175-186; Ciriello, V.M., 2003. The effects of box size, frequency, and extended horizontal reach on maximum acceptable weights of lifting. Int. J. Ind. Ergon. 32, 115-120). Lastly, we studied the effects of high frequency (20 lifts/min) on MAWs of lifting. Ten female industrial workers performed 15 variations of lifting using our psychophysical methodology whereby the subjects were asked to select a workload they could sustain for 8h without "straining themselves or without becoming unusually tired weakened, overheated or out of breath". The results confirmed that MAWs of lifting with the large box was significantly effected by frequency. The frequency factor pattern in this study was similar to the frequency pattern from a previous study using the small box (Ciriello, V.M., Snook, S.H., 1983. A study of size distance height, and frequency effects on manual handling tasks. Hum. Factors 25(5), 473-483) for all fast frequencies down to one lift every 2 min with deviations of 7%, 15%, and 13% for the one lift every 5 and 30 min tasks and the one lift in 8h task, respectively. The effects of lifting with an extended horizontal reach decreased MAW 22% and 18% for the mid and center lift and the effects of the 20 lifts/min frequency resulted in a MAW that was 47% of a 1 lift/min MAW. Incorporating these results in future guidelines should improve the design of MMH tasks for female workers.

Female↗
PubMed1998

Asymmetric low back loading in asymmetric lifting movements is not prevented by pelvic twist.

Asymmetric lifting is associated with an increased risk of low back disorders. Especially in lifting movements, characterized by a small amount of asymmetry, it is still the question if asymmetric lumbosacral torques occur, or if subjects try to avoid asymmetric back loading by twisting their pelvis with respect to the feet. An increase of the lifting speed or the box weight might amplify the lumbar torques but might also result in an attempt to limit further increase of asymmetric torques by increasing pelvic twist. In the current study, asymmetrical lifting movements were analyzed with the aid of a 3D linked segment model, using cuffs mounted to the body segments. Eight subjects performed lifting movements with five different asymmetry conditions, ranging from 0 to 90 degrees lifting asymmetry with respect to the sagittal plane, using two lifting speeds and two box weights. A significant increase in lateral flexing and twisting low back torque was found for each increase in asymmetry of the lifting movement. Pelvic twist accounted more or less constantly for about 25% of the lifting asymmetry and was hardly influenced by lifting speed or box weight. Even for 10 or 30 degrees of lifting asymmetry, subjects did not twist their pelvis far enough to avoid asymmetric loading of the low back. Assuming that asymmetric loading of the low back is more strenuous to the spine than symmetric loading, the current results indicate that even small deviations of a lifting movement from the sagittal plane can explain an increased risk of low back disorders.

Back↗
PubMed1999

Stoop or squat: a review of biomechanical studies on lifting technique.

OBJECTIVE: To assess the biomechanical evidence in support of advocating the squat lifting technique as an administrative control to prevent low back pain. BACKGROUND: Instruction with respect to lifting technique is commonly employed to prevent low back pain. The squat technique is the most widely advised lifting technique. Intervention studies failed to show health effects of this approach and consequently the rationale behind the advised lifting techniques has been questioned. METHODS: Biomechanical studies comparing the stoop and squat technique were systematically reviewed. The dependent variables used in these studies and the methods by which these were measured or estimated were ranked for validity as indicators of low back load. RESULTS: Spinal compression as indicated by intra-discal pressure and spinal shrinkage appeared not significantly different between both lifting techniques. Net moments and compression forces based on model estimates were found to be equal or somewhat higher in squat than in stoop lifting. Only when the load could be lifted from a position in between the feet did squat lifting cause lower net moments, although the studies reporting this finding had a marginal validity. Shear force and bending moments acting on the spine appeared lower in squat lifting. Net moments and compression forces during lifting reach magnitudes, that can probably cause injury, whereas shear forces and bending moments remained below injury threshold in both techniques. CONCLUSION: The biomechanical literature does not provide support for advocating the squat technique as a means of preventing low back pain. RELEVANCE: Training in lifting technique is widely used in primary and secondary prevention of low back pain, though health effects have not been proven. The present review assesses the biomechanical evidence supporting the most widely advocated lifting technique.

Biomechanical Phenomena↗
PubMed2003

Body motion during repetitive isodynamic lifting: a comparative study of normal subjects and low-back pain patients.

To quantify performance differences between patients with low-back pain (LBP) and a control group during their performance of a repetitive isodynamic lifting task. Case-control study was done. LBP patients were recruited and tested at an outpatient ambulatory chronic pain rehabilitation program before treatment was begun. Fifty-three LBP patients who had prolonged back pain and 53 age and gender matched pain-free control subjects. Overall lifting performance measures included weight lifting and number of lifts completed; kinematic measures of hip and knee movements during lifting were described by hyperbolic tangent models, and included static measures of starting and ending angles, and dynamic measures of midpoint, falltime, and lift speed. Control subjects completed significantly more lifts and lifted more weight than patients. Starting hip flexion was greater for controls and starting knee flexion was greater for patients, indicating that patients used more of a leg lift. Patients and controls also differed significantly on dynamic measures, particularly lifting speed and hip and knee temporal midpoints. Major static and dynamic motion differences were found between LBP patients and controls as they performed repetitive lifting under a constant load. These findings indicate that body motion parameters, in addition to more common strength and endurance measures, are necessary to describe the impact of persistent LBP on a person's lifting abilities.

Adult↗
PubMed1999

A biomechanical evaluation of lifting speed using work- and moment-related measures.

A biomechanical evaluation of lifting speed was conducted in the laboratory. The study investigated the effects of lifting speed on several predetermined biomechanical cost functions. The lifting tasks consisted of five lifting speeds labelled as the slowest, slow, normal, fast and fastest, and three weights, 50, 65 and 80% of their maximum acceptable weight of lift. The speed at each level was determined individually by each subject according to their capability. The study found that work-related measures, including the total net muscle work, total absolute net muscle work and work done to the load, decreased significantly as the lifting speed increased (p < 0.05, < 0.001 and < 0.001, respectively). The time integral of sum of squared ratio of joint moment and strength also decreased significantly (p < 0.001). This indicates that lifting at a faster speed tends to reduce the work the body has to do. The peak speed of load occurred at 70% of total lifting time for the slowest lifts, but at 30% of total lifting time for other lifting speeds. Performing lifts at the minimum speeds changed the usual speed coordination technique the subjects used.

Adult↗
PubMed1999

Psychophysically determined infrequent lifting capacity of Chinese participants.

The aim of this study was to investigate the psychophysical infrequent lifting capacity (maximum acceptable weight of lift, MAWL) for a Chinese population. A nested-factorial experimental design with a participant factor nested within gender was employed. Forty-one Chinese participants (29 males, 12 females) participated in the study. Two frequencies (one lift every 8 h and one lift every 5 min) and six lifting heights (floor to knuckle, floor to shoulder, floor to reach, knuckle to shoulder, knuckle to reach, shoulder to reach) were evaluated. The results are compared with prior studies and they lead to the following conclusions. (1) The MAWLs were significantly affected by both the lifting frequency and lifting height. For lifting frequency, the MAWLs decreased markedly by nearly 30% from one lift every 8 h to one lift every 5 min. For lifting height, the MAWLs of the F-K was the greatest of all six lifting heights, followed by F-S, K-S, F-R, K-R and S-R was the smallest. (2) The MAWLs for Chinese females are significantly lower, but proportionately similar, to the MAWLs for Chinese males. (3) The Chinese participants had smaller capacities compared with the Occidental participants, and the rate of decrease in MAWL for the Chinese participants was much sharper than that of Occidental participants. (4) The MAWL of Chinese females was about 54-58% of the Chinese males, it is somewhat lower than those of 60-70% of the Occidental participants.

Adult↗
PubMed1999

The effects of lifting speed on the peak external forward bending, lateral bending, and twisting spine moments.

Lifting tasks that involve twisting have been repeatedly implicated as contributing to the onset of occupational back injuries in epidemiological studies. The objective of this work was to quantify the three directional external moments acting on the spine during a sagittally symmetric and two asymmetric lifting tasks. A total of 15 subjects participated in the three lifting tasks. All tasks were performed at two qualitatively defined lifting speeds, 'slow' and 'fast', and with two load magnitudes: 10 and 20% of the subject's body weight. The mid-sagittal plane lifts were performed using two horizontal reach distances: 40 and 60 cm. A four-camera, two-forceplate motion and force measurement system were used to obtain the kinematic and kinetic data as the lifts were performed. A dynamic link-segment biomechanical model was used to quantify the reaction forces and moments at the ankle, knee, and hip and L5/S1 joints. Results from all tasks showed increased sagittal plane (forward bending) spine moments with the heavier load and at the faster lifting speed (p < 0.001). Spine lateral bending and twisting moments increased during the mid-sagittal plane lifts with the greater reach distance and the faster lifting speed, respectively. The twisting moments on the spine were greatest as subjects lifted from in front and placed the load to the side but were dependent upon the lifting speed and the load magnitude. The lateral bending moments increased during this same task with the heavier load. However, the spine lateral bending moments were greatest when lifting from one side to the other.

Adult↗