Static Lift Research Articles

Comparison of trunk muscle forces and spinal loads estimated by two biomechanical models

Background Comparative studies between single-joint electromyography (EMG)- and optimization-driven models of the human spine in estimating trunk muscle and spinal compression forces have not been conclusive. Due to associated implications in ergonomic applications as well as prevention and treatment managements of low-back disorders, there is a need to critically compare existing single- and multi-joint spine models. Methods A comprehensive comparison of muscle forces and spinal loads estimated by a single-joint (L5–S1 or L4–L5) EMG-driven model (EMGAO) and a multi-joint (T1–S1) Kinematics-driven finite element model (KD) of the spine under different static lifting activities in upright standing posture is carried out. Identical geometry for the spine and trunk musculature as well as passive properties are used in both models. Required model inputs including kinematics, force plate and surface EMG data are collected from one asymptomatic male subject. Findings Contrary to somewhat similar external moments (with differences <11 Nm) as well as comparable compression forces at the L4–S1 joints (<20% except in the heaviest task with 52% difference) and sum of all trunk muscle forces (<26% except in the heaviest task with 44% difference), both models recruited trunk global and local lumbar muscles in markedly different proportions (ratio of total global over total local muscle forces in cases with load in hands remained >2.4 in the KD model whereas <1.0 in the EMGAO model) which in turn led to significantly different shear force estimates. Results of the EMGAO model were level dependent. Estimated L4–L5 intradiscal pressures were comparable to the measured data except for the heaviest task in which case the EMGAO model overestimated the measured pressure by 67%. Interpretation Differences in predictions between these modeling approaches vary depending on the task simulated and the joint considered in the single-joint models of the spine. Such studies are essential to critically evaluate relative performance of existing models and to propose modifications to improve accuracy in estimations. Ergonomic and clinical applications of such model studies should, hence, be carried out with due attention to associated underlying assumptions and shortcomings.

A calculation method for parametric design studies of V/STOL aircraft

AbstractThis paper provides a method that helps the aircraft designer to develop a performance constraint chart (PCC) for vertical/short takeoff and landing (V/STOL) aircraft that produce hybrid lift (static lift in combination with aerodynamic lift). The PPC provides a first estimation for the thrust-to-weight ratio (T0/MTOW) and wing loading (MTOW/S). The method is applicable to concepts, where static lift and main-engine thrust are coupled (e.g. the F-35B system, turbojet and lift-fan, coupled by a shaft) and to concepts, where static lift is produced by separate devices (e.g. lift-engines or other concepts for static lift). It includes thrust vectoring of the main engine.The method includes the evaluation of certain flight stages, or segments, as short take-off and landing (STOL), vertical landing (VL), one engine inoperative (OEI) climb (for civil aircraft concept applications) and cruise, all these have to be considered. For each of these five segments, standard flight mechanics equations are extended by a static lift component, an augmentation ratio (a factor that describes the dependency of the thrust and the static lift, if coupled) and the thrust vectoring angle. Hence these equations are modified in a way that the aircraft designer can directly calculate T0/MTOW and MTOW/S for the performance requirements of each segment. Thus, an optimum design point can be selected. Inputs are aerodynamic coefficients, maximum lift coefficient of the wing, mass fraction from take-off to landing, additional static lift during take-off and landing, number of engines, augmentation ratio of the propulsion system and required take-off and landing field length.A performance constraint chart for a JSF F-35B type aircraft is modelled to show the application of the method. As an application to civil aircraft a PCC and a parameter optimisation for the civil regional jet ‘HyLiner’ is presented.

Galloping analysis of stranded electricity conductors in skew winds

When first commissioned, the 1.6 km span 275kV Severn Crossing Conductor experienced large amplitude vibrations in certain wind conditions, but without ice or rain, leading to flashover between the conductor phases. Wind tunnel tests undertaken at the time identified a major factor was the lift generated in the critical Reynolds number range in skew winds. Despite this insight, and although a practical solution was found by wrapping the cable to change the aerodynamic profile, there remained some uncertainty as to the detailed excitation mechanism. Recent work to address the problem of dry inclined cable galloping on cable-stayed bridges has led to a generalised quasi-steady galloping formulation, including effects of the 3D geometry and changes in the static force coefficients in the critical Reynolds number range. This generalised formulation has been applied to the case of the Severn Crossing Conductor, using data of the static drag and lift coefficients on a section of the stranded cable, from the original wind tunnel tests. Time history analysis has then been used to calculate the amplitudes of steady state vibrations for comparison with the full scale observations. Good agreement has been obtained between the analysis and the site observations, giving increased confidence in the applicability of the generalised galloping formulation and providing insight into the mechanism of galloping of yawed and stranded cables. Application to other cable geometries is also discussed.

A physical demands analysis of the 24-week British Army Parachute Regiment recruit training syllabus

This study assessed the physical demands of the 24-week Combined Infantryman's Course (CIC) for Parachute Regiment (Para) recruits and developed physical selection standards for applicants. Fifty recruits were monitored over five separate periods (35 d in total during weeks 1–2, 5, 9, 15 and 19–20). Energy expenditure (doubly labelled water), physical activity (accelerometry) and cardiovascular strain (% heart rate reserve) were measured. There was no overall progression in both the levels of physiological stress (physical activity counts and energy expenditure) and resultant cardiovascular strain during the first nine weeks of training. Applicants' 2.4 km run time and static lift strength measured at selection predicted 10 mile loaded march performance at the end of CIC Para. The introduction of job-related selection procedures and a more progressive approach to training has reduced the incidence of medical discharge from 14.4% to 5.1% and increased overall pass rates from 43% to 58%.

Static thrust recovery of PAR craft on solid surfaces

Power-Augmented-Ram Vehicles belong to a new class of ground-effect machines with hybrid support. Recovered static thrust and static lift on solid surfaces are important amphibious characteristics of this craft. Experimental data for the static thrust recovery and the transition to a hovering mode are obtained in the tests with a vehicle model on two types of ground surface and with variable engine thrust and flap trailing-edge gap. The uphill surface and increased mass of the model demonstrate reductions in thrust recovery. A comparison with a two-dimensional potential-flow theory is presented. The static thrust accumulation, identified in the pre-hovering regime of a model on solid surface, does not significantly benefit the low-speed forward motion.

Dynamic lift measurements on a FX79W151A airfoil via pressure distribution on the wind tunnel walls

We report on an experimental setup for measurements of dynamic stall for airfoils via the pressure distribution over wind tunnel walls. This measuring technique, hitherto used for lift measurements under static conditions, is also an adequate method for dynamic conditions until stall occurs. A step motor is used, allowing for sinusoidal as well as non-sinusoidal and stochastic pitching to simulate fast fluctuating flow conditions. Measurements with sinusoidal pitching and constant angular velocities were done and show dynamic stall characteristics. Under dynamic stall conditions, maximum lift coefficients were up to 80% higher than the maximum for static lift.

Dynamic stall model for wind turbine airfoils

Abstract A model is presented for aerodynamic lift of wind turbine profiles under dynamic stall. The model combines memory delay effects under attached flow with reduced lift due to flow separation under dynamic stall conditions. The model is based on a backbone curve in the form of the static lift as a function of the angle of attack. The static lift is described by two parameters, the lift at fully attached flow and the degree of attachment. A relationship between these parameters and the static lift is available from a thin plate approximation. Assuming the parameters to be known during static conditions, nonstationary effects are included by three mechanisms: a delay of the lift coefficient of fully attached flow via a second-order filter, a delay of the development of separation represented via a first-order filter, and a lift contribution due to leading edge separation also represented via a first-order filter. The latter is likely to occur during active pitch control of vibrations. It is shown that all included effects can be important when considering wind turbine blades. The proposed model is validated against test data from two load cases, one at fully attached flow conditions and one during dynamic stall conditions. The proposed model is compared with five other dynamic stall models including, among others, the Beddoes–Leishman model and the ONERA model. It is demonstrated that the proposed model performs equally well or even better than more complicated models and that the included nonstationary effects are essential for obtaining satisfactory results. Finally, the influence of camber and thickness distribution on the backbone curve are analysed. It is shown that both of these effects are adequately accounted for via the static input data.

Test-retest reliability of psychophysical lift capacity in patients with non-specific chronic low back pain and healthy subjects

Psychophysical lift capacity tests are lifting tests in which the performance, expressed in Newtons, is divided by the perceived exertion, expressed on a Borg scale. The aim of this study was to analyse test-retest reliability of psychophysical lift capacity tests. Patients with non-specific chronic low back pain (n=20) and healthy subjects (n=20). Psychophysical lift capacity tests were assessed during a back school intake at the Centre for Rehabilitation of the University Medical Centre Groningen. Patients on the waiting list and healthy subjects were assessed twice, with a 2-week interval between assessments. Intra-class correlation (ICC) was calculated as a measure of reliability. An ICC > or = 0.75 was considered as an acceptable reliability. Limits of agreement as a measure for natural variation were calculated. The psychophysical static and dynamic lift capacity tests showed good reliability (ICC > or = 0.75). The limits of agreement are substantial, indicating a considerable natural variation between test-sessions for all psychophysical tests. The psychophysical static lift capacity and dynamic lifting capacity are reliable instruments for patients with non-specific chronic low back pain and healthy subjects. However, a substantial amount of natural variation should be taken into account between 2 test sessions when interpreting the test results clinically.

Wrapping of trunk thoracic extensor muscles influences muscle forces and spinal loads in lifting tasks

An improved assessment of risk of spinal injury during lifting activities depends on an accurate estimation of trunk muscle forces, spinal loads and stability margin which in turn requires, amongst others, an accurate description of trunk muscle geometries. The lines of action of erector spinae muscles are often assumed to be linear despite the curved paths of these muscles in forward flexion postures. A novel approach was introduced that allowed for the proper simulation of curved paths for global extensor muscles in our Kinematics-driven finite element model. The lever arms of global muscles at different levels were restrained either to remain the same or decrease only by 10% relative to their respective values in upright posture. Based on our earlier measurements, static lifting tasks at two trunk flexions (40 degrees and 65 degrees ) and three lumbar postures (free style, lordotic and kyphotic) with 180 N in hands were analyzed. Muscle forces and spinal compression at all levels substantially decreased as the global extensor muscles took curved paths. In contrast, the shear force at lower levels increased. Allowing for a 10% reduction in these lever arms during flexion increased muscle forces and compression forces at all levels. Despite smaller muscle forces, wrapping of global muscles slightly improved the spinal stability. Consideration of global extensor muscles with curved paths and realistic lever arms is important in biomechanical analysis of lifting tasks. Reduction in the erector spinae lever arms during flexion tasks could vary depending on the lumbar posture. Results advocate small flattening of the lumbar curvature in isometric lifts yielding smaller compression and shear forces at the critical L5-S1 level.

Effect of Previous Unilateral Injuries on Ground Reaction Force Asymmetries during Static Lifting

Fluctuating asymmetries occur as a natural part of growth and development. As a result, functional asymmetries, expressed by placing greater forces on one side of the body, may be expected during otherwise seemingly symmetric tasks. The presence of a unilateral injury (lower or upper extremity) may increase the magnitude of asymmetry. However, after recovery, it is not clear if a person would be more asymmetric than someone that had never experienced a significant injury. PURPOSE: The goal of this investigation was to compare bilateral vertical ground reaction forces during a maximum effort static lifting task in workers either a healed/ non-bothersome previous unilateral injury (PUI) or without (NPUI). METHODS: After screening with a health history interview, 22 firefighters were classified with PUI (age = 44+/−9 yrs, height = 178+/−10 cm, mass = 84.2+/−14.7kg (Mean +/− SD)) and 17 NPUI (age = 41+/−7yrs, height = 178+/−6 cm, mass = 84.5+/−11.5 kg). All subjects lifted using a symmetric stance with feet roughly shoulder width apart. Each foot was placed on a separate force platform. The hips and knees were slightly flexed with the back straight so that subjects pulled upward on a hand grip that was slightly above knee level. After warm-up and familiarization, three maximal effort lifts were made with rest in between. Each maximal effort lasted three seconds with the highest one second average extracted. From these, the best lift was analyzed. Statistical significance was set atp <0.05. RESULTS: There was no difference in hip and knee angle, or pulling force between groups. All subjects except for one in each group favored one side of the body while lifting (different from 50.0/50.0%) with the most asymmetric differing by 10% (PUI=54.6/45.4%, NPUI=55.0/45.0%). On average, levels of asymmetry were not different between groups (PUI=51.1+/−1.1%, NPUI=51.2+/−1.2%, p=0.718). There was no tendency for the NPUI subjects to exert more force on the uninjured side compared to the previously injured side (50.2/49.8+/−1.6%, p=0.563). However, NPUI subjects produced significantly greater forces under their non-kicking leg compared to their preferred kicking leg (50.9/49.1+/−1.5%, p=0.029) while PUI subjects did not (50.5/49.5+/−1.5%, p=0.124). CONCLUSIONS: Based on the symmetric nature of the task, it was not surprising to find relatively low levels of asymmetry in both groups. However, a PUI does appear to disrupt the natural relationship that develops between the dominant and non-dominant leg of the lower extremities. Therefore, future research is needed to elucidate the effect this may have on both performance and injury risk for a person with a PUI.

Reliability and Validity of Low Back Strength/Muscular Endurance Field Tests in Adolescents

Background:Strength, muscular endurance, and flexibility are important components of healthy back function. This study determined the reliability and evaluated the validity of selected low back field tests (FITNESSGRAM® Trunk Extension [FG-TE] and Box 90° Dynamic Trunk Extension [B-90° DTE]) when compared to laboratory tests (Parallel Roman Chair Dynamic Trunk Extension [PRC-DTE], Parallel Roman Chair Static Trunk Extension [PRC-STE], and Dynamometer Static Back Lift [DSBL]).Methods:Forty males age 15.1 ± 1.2 yr and 32 females age 15.5 ± 1.2 yr participated.Results:Intraclass test-retest reliability coefficients (one-way ANOVA model for a single measure) ranged from .940 to .996. Validity coefficients determined by Pearson product moment correlation coefficients for males and females, respectively, were as follows: B-90° DTE vs. PRC-DTE = .82, .62 (p &lt; .05); B-90° DTE vs. PRC-STE = .55, .38 (p &lt; .05); B-90° DTE vs. DSBL = −.29, −.23; FG-TE vs. PRC-DTE = .23, −.11; FG-TE vs. PRC-STE = −.15, .33; and FG-TE vs. DSBL = −.04, −.36.Conclusions:B-90° DTE was shown to be a valid field test when compared to PRC-DTE, but only for the males. Further research on the PRC-DTE and PRC-STE items for adolescents is recommended.

The static and dynamic lifting capacity in patients with chronic low back pain

The static and dynamic lifting capacity in patients with chronic low back pain

Role of intra-abdominal pressure in the unloading and stabilization of the human spine during static lifting tasks

The role of intra-abdominal pressure (IAP) in unloading the spine has remained controversial. In the current study, a novel kinematics-based approach along with a nonlinear finite-element model were iteratively used to calculate muscle forces, spinal loads, and stability margin under prescribed postures and loads measured in in vivo studies. Four coactivity levels (none, low, moderate, and high) of abdominal muscles (rectus abdominis, external oblique, and internal oblique) were considered concurrently with a raise in IAP from 0 to 4 kPa when lifting a load of 180 N in upright standing posture and to 9 kPa when lifting the same load in forward trunk flexions of 40 degrees and 65 degrees. For comparison, reference cases with neither abdominal coactivity nor IAP were investigated as well. A raise in IAP unloaded and stabilized the spine when no coactivity was considered in the foregoing abdominal muscles for all lifting tasks regardless of the posture considered. In the upright standing posture, the unloading action of IAP faded away even in the presence of low level of abdominal coactivity while its stabilizing action continued to improve as abdominal coactivity increased to moderate and high levels. For lifting in forward-flexed postures, the unloading action of IAP disappeared only with high level of abdominal coactivities while its stabilizing action deteriorated as abdominal coactivities increased. The unloading and stabilizing actions of IAP, hence, appear to be posture and task specific.

Biomechanics of Changes in Lumbar Posture in Static Lifting

In vivo measurements and model studies are combined to investigate the role of lumbar posture in static lifting tasks. Identification of the role of changes in the lumbar posture on muscle forces, internal loads, and system stability in static lifting tasks with and without load in hands. Despite the recognition of the causal role of lifting in spinal injuries, the advantages of preservation or flattening of the lumbar lordosis while performing lifting tasks is not yet clear. Kinematics of the spine and surface EMG activity of selected muscles were measured in 15 healthy subjects under different forward trunk flexion angles and load cases. Apart from the freestyle lumbar posture, subjects were instructed to take either lordotic or kyphotic posture as well. A kinematics-based method along with a nonlinear finite element model were interactively used to compute muscle forces, internal loads and system stability margin under postures, and loads considered in in vivo investigations. RESULTS.: In comparison with the kyphotic postures, the lordotic postures increased the pelvic rotation, active component of extensor muscle forces, segmental axial compression and shear forces at L5-S1, and spinal stability margin while decreasing the passive muscle forces and segmental flexion moments. Alterations in the lumbar lordosis in lifting resulted in significant changes in the muscle forces and internal spinal loads. Spinal shear forces at different segmental levels were influenced by changes in both the disc inclinations and extensor muscle lines of action as the posture altered. Considering internal spinal loads and active-passive muscle forces, the current study supports the freestyle posture or a posture with moderate flexion as the posture of choice in static lifting tasks.

Sensitivity of kinematics-based model predictions to optimization criteria in static lifting tasks

The effect of eight different cost functions on trunk muscle forces, spinal loads and stability was investigated. Kinematics-based approach combined with nonlinear finite element modeling and optimization were used to model in vivo measurements on isometric forward flexions at ∼40° and ∼65° in sagittal plane with or without a load of 180 N in hands. Four nonlinear (∑stress 3, ∑stress 2, ∑force 2 and muscle fatigue) and four linear (∑stress, ∑force, axial compression and double-linear) criteria were considered. Predicted muscle activities were compared with measured EMG data. All predictions, irrespective of the cost function used, satisfied required kinetic, kinematics and stability conditions all along the spine. Four criteria (∑stress 3, ∑stress 2, fatigue and double-linear) predicted muscle activities that qualitatively matched measured EMG data. The fatigue and double-linear criteria were inadequate in predicting greater forces in larger muscles with no consideration for their moment arms. Nearly the same stability margin was computed under these four cost functions. At the lower lumbar levels, the compression forces differed by <20% and the shear forces by <14% as various cost functions were considered. Smaller axial compression and anterior shear forces (by ⪝6%) were computed when only the active components rather than the total muscle forces were taken as unknown in the ∑stress 3 cost function. Overall, one single cost function of ∑stress 2 or ∑stress 3 rather than a multi-criteria one was found sufficient and adequate in yielding plausible results comparable with measured EMG activities and disc pressure.

21307 非調和的ピッチング運動をする円盤に働く非定常流体力測定(流体工学(2))

Unsteady fluid forces acting on a disc with several anharmonic periodic pitching motions under conditions of several frequencies were measured by using load cell in a wind tunnel at Re numbers 1.0×10^5 and 2.0×10^5. Dynamic lift/drag coefficients were compared with the steady ones. Moreover, we investigated the ratio between maximum dynamic lift and maximum quasi static lift versus reduced frequencies. The results showed that the dynamic lift/drag coefficient curves in the anharmonic pitching motion were only shifted compared with those in the sinusoidal pitching motion. However, it was found that the fast up-stroke gave high maximum dynamic lift coefficient.

Lifting strengths decrease with the extent of squat postures

The objective of this study was to examine the effects of different squat postures on maximum static lifting strengths. Ten experienced healthy male lifters were examined on their maximum static two-handed lifting strengths and associated elbow, shou

Do medical factors predict disability in older adults with persistent low back pain?

Persistent low back pain (LBP) is one of the most common and challenging persistent pain conditions in older adults. Medical comorbidity also is common in these individuals, but its impact on disability has not been examined. The purpose of this study was, using a cross-sectional design, to examine the functional impact of pain-related and general medical comorbidity on 100 community dwelling older adults (mean age 74.3) with persistent mechanical LBP. Subjects received a structured history and physical examination, lumbosacral spine X-rays, and standardized tests of physical function. Pain-related variables included intensity, duration, extent, and lumbar motion-induced pain. General medical variables included age, comorbidity, number of medications, depressive symptoms, back range of motion, body mass index, and severity of radiographic pathology. Function/disability measures included self-reported disability, gait speed, and mean number of static lifts and amount of work performed during a dynamic lifting task. Structural equation modeling was used to evaluate the influence of pain and medical variables on function/disability. The overall regression model indicated pain and medical variables were significantly associated with function/disability measures ( R 2=0.45, P<0.01). Individual regression coefficients, however, indicated that only pain duration ( r=−0.36, P<0.05) and pain severity ( r=0.37, P<0.001) were significantly associated with function/disability. Despite the prevalence of medical co-morbidities in older PLBP subjects, they appear to be of limited utility in understanding level of disability. These findings also underscore the need to optimize pain treatment in independent older adults to optimize physical function and delay the onset of dependent living status.

Static lifting strengths at different exertion heights

Twelve healthy right-handed male subjects were recruited to investigate their maximum static lifting strengths for right-handed, left-handed and two-handed exertions at five different exertion heights (10, 45, 75, 105, and 140 cm). The results showed that the highest lifting strength occurred in the interval of exertion height between 10 and 45 cm while the lowest lifting strength at the exertion height of 105 cm. The hand dexterity seemed to have little connection with lifting strengths especially for higher exertion heights. This study suggests that two-handed lifting should be encouraged since it resulted in both higher lifting strengths and less strains on load-bearing shoulder, elbow and wrist structures compared with one-handed lifting. Additionally, the sum of right-handed and left-handed lifting strengths was greater than the two-handed lifting strength for exertion height below 75 cm, while it was smaller than the two-handed lifting strength at 140 cm exertion height. Relevance to industry This study provides the lifting strength data for one-handed and two-handed manual lifting tasks. Practitioners can use the results of this study for ergonomic design of manual lifting tasks and equipments in industry.

Assessment of disability: Do medical factors predict disability in older adults with low back pain?

Chronic low back pain (CLBP) is one of the most common and challenging persistent pain conditions in older adults. Medical co-morbidity is common in these individuals, but its impact on disability has not been examined. The purpose of this study was, using a cross-sectional design, to examine the functional impact of pain-related and general medical co-morbidity on 70 community dwelling older adults (M age 73.9) with chronic mechanical LBP (at least moderate pain intensity on most days for at least 3 months). Subjects received a structured history and physical examination, lumbosacral spine x-rays, standardized tests of physical function, and a laboratory based measure of physical capacity (repetitive isodynamic lifting). Pain-related variables included intensity (MPQ-SF), duration, extent (number of painful body sites), and lumbar motion-induced pain. General medical variables included age, cumulative illness rating scale score, number of medications, back range of motion, body mass index, and severity of radiographic pathology. Functional measures included 2 self-reported disability scales (Roland; Jette FSI), gait speed, mean number of static lifts, and amount of work performed during a dynamic lifting task. Structural equation modeling was used to evaluate the influence of pain and medical variables on functional measures. The overall regression model indicated pain and medical variables were significantly associated with functional measures (R2 = .33, p < .01). Individual regression paths, however, indicated that only pain duration (r = -.35, p < .01) and pain severity (r = .33, p < .05) were significantly associated with functional measures. Thus, despite the prevalence of medical co-morbidities in older CLBP subjects, this study suggests that these measures are of limited utility in understanding level of disability. These findings also underscore the need to optimize pain treatment for these individuals so as to optimize physical function and, hopefully, delay the onset of dependent living status.