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

Multi-phase optimisation model predicts manual lifting motions with less reliance on experiment-based posture data

Optimisation-based predictive models are widely-used to explore the lifting strategies. Existing models incorporated empirical subject-specific posture constraints to improve the prediction accuracy. However, over-reliance on these constraints limits the application of predictive models. This paper proposed a multi-phase optimisation method (MPOM) for two-dimensional sagittally symmetric semi-squat lifting prediction, which decomposes the complete lifting task into three phases-the initial posture, the final posture, and the dynamic lifting phase. The first two phases are predicted with force- and stability-related strategies, and the last phase is predicted with a smoothing-related objective. Box-lifting motions of different box initial heights were collected for validation. The results show that MPOM has better or similar accuracy than the traditional single-phase optimisation (SPOM) of minimum muscular utilisation ratio, and MPOM reduces the reliance on experimental data. MPOM offers the opportunity to improve accuracy at the expense of efforts to determine appropriate weightings in the posture prediction phases. Practitioner summary: Lifting optimisation models are useful to predict and explore the human motion strategies. Existing models rely on empirical subject-specific posture constraints, which limit their applications. A multi-phase model for lifting motion prediction was constructed. This model could accurately predict 2D lifting motions with less reliance on these constraints.

Psoas major and lumbar lordosis may correlate with pain episodes during Sorensen test in patients with non-specific low back pain

BACKGROUND

The reason that participants develop pain episodes during the Sorensen test remains unclear. Lumbar lordosis and trunk muscle are important for dynamic stability of the spine; however, their role in pain episodes during the Sorensen test has not yet been discussed.

OBJECTIVE

To investigate the effects of muscular morphology and lumbar curvature on pain development during the Sorensen test in patients with non-specific low back pain (LBP).

METHODS

Ninety-one patients diagnosed with chronic non-specific LBP and underwent the Sorensen test were enrolled. Lumbar lordosis, cross-sectional area and fat infiltration rate of trunk muscle and centroid line of psoas major (dividing into three types: anterior arc, linear and posterior arc) were measured using ImageJ software. All recruited patients were grouped into pain episode and exhaustion groups and were matched for the confounders based on propensity scores. The above parameters were compared between groups and further adjusted for confounding bias.

RESULTS

After adjustment , the mean differences in lumbar lordosis of 12.1 ± 2.3∘ between the two groups in the complete cohort and of 13.9 ± 2.5∘ in the matching cohort remained significant, the exhaustion group had a 0.22-fold and 0.08-fold risk of presenting as linear and posterior arc types, respectively, compared with the pain episode group in the complete cohort (p= 0.008, p= 0.004), the corresponding values were 0.19-fold and 0.05-fold, respectively, in the matching cohort (p= 0.014, p= 0.010). Logistic regression demonstrated that lumbar lordosis, the linear and posterior arc types were significantly associated with pain episode during the test (OR = 0.78, p< 0.001; OR = 4.50, p= 0.038; OR = 9.93, p= 0.033).

CONCLUSIONS

Lower lumbar lordosis and linear and posterior arc types of the psoas major centroid line were possibly relevant to the pain episode during Sorensen test in patients with chronic non-specific LBP.

Thoracolumbar And Lumbopelvic Spinal Alignment During The Deadlift Exercise: A Comparison Between Men And Women

Background

A neutral spinal alignment is considered important during the execution of the deadlift exercise to decrease the risk of injury. Since male and female powerlifters experience pain in different parts of their backs, it is important to examine whether men and women differ in spinal alignment during the deadlift.

Objectives

The purpose of this study was to quantify the spinal alignment in the upper (thoracolumbar, T11-L2) and lower (lumbopelvic, L2-S2) lumbar spine during the deadlift exercise in male and female lifters. Secondary aims were to compare lumbar spine alignment during the deadlift to standing habitual posture, and determine whether male and female lifters differ in these aspects.

Study Design

Observational, Cross-sectional.

Methods

Twenty-four (14 men, 10 women) lifters performed three repetitions of the deadlift exercise using 70% of their respective one-repetition maximum. Spinal alignment and spinal range of motion were measured using three inertial measurement units placed on the thoracic, lumbar and sacral spine. Data from three different positions were analyzed; habitual posture in standing, and start and stop positions of the deadlift, i.e. bottom and finish position respectively.

Results

During the deadlift, spinal adjustments were evident in all three planes of movement. From standing habitual posture to the start position the lumbar lordosis decreased 13° in the upper and 20° in the lower lumbar spine. From start position to stop position the total range of motion in the sagittal plane was 11° in the upper and 22° in the lower lumbar spine. The decreased lumbar lordosis from standing habitual posture to the start position was significantly greater among men.

Conclusions

Men and women adjust their spinal alignment in all three planes of movement when performing a deadlift and men seem to make greater adjustments from their standing habitual posture to start position in the sagittal plane.

Level of Evidence

3.

The quantified lumbar flexion-relaxation phenomenon is a useful measurement of improvement in a functional restoration program

STUDY DESIGN

A prospective cohort study evaluating the quantitative lumbar flexion-relaxation phenomenon (QLFRP), measured with surface electromyographic (SEMG) signals from the erector spinae during trunk flexion pre- and postrehabilitation, in patients with chronic disabling occupational lumbar disorders (CDOLD).

OBJECTIVES

To assess the responsiveness of the QLFRP in documenting change in functional performance during a functional restoration program for CDOLD patients.

SUMMARY OF BACKGROUND DATA

A recent theoretical construct suggests that QLFRP is responsive to change in lumbar range of motion (ROM) during rehabilitation, with high sensitivity and specificity for abnormal QLFRP predicting ROM.

METHODS

A cohort of normal subjects was tested for QLFRP correlated to inclinometric lumbar ROM measures. The cutoff score was applied to a group of CDOLD patients entering a functional restoration program (N = 135), and to program completers (N = 104). Pain and functional self-report scores were compared with SEMG and ROM measures.

RESULTS

The CDOLD group averaged 23.7 months off work. Surgical treatment was provided prerehabilitation to 51% of patients, with 29% receiving lumbar fusions. From pre- to post-treatment, achievement of QLFRP rose from 31% to 74% of patients, while normal ROM rose from 8% to 63% of patients. Compared to the 16% of patients still demonstrating both abnormal QLFRP and ROM, the other groups showed significantly greater improvement in self-reported pain and function, with the best improvements occurring in patients showing normal ROM and QLFRP. The QLFRP showed high sensitivity, but only modest predictive validity and specificity for predicting ROM postrehabilitation. Improvement in sensitivity and predictive validity occur when surgical cases were excluded from the analysis.

CONCLUSION

A majority of patients in an interdisciplinary functional restoration program failed to demonstrate either the QLFRP or normal ROM on admission to the program. A majority of program completers, however, achieved both normal ROM and QLFRP and another 30% demonstrated either normal QLFRP or normal ROM. Both QLFRP and ROM measures were responsive to relevant self-report scales.

Analysis of squat and stoop dynamic liftings: muscle forces and internal spinal loads

Despite the well-recognized role of lifting in back injuries, the relative biomechanical merits of squat versus stoop lifting remain controversial. In vivo kinematics measurements and model studies are combined to estimate trunk muscle forces and internal spinal loads under dynamic squat and stoop lifts with and without load in hands. Measurements were performed on healthy subjects to collect segmental rotations during lifts needed as input data in subsequent model studies. The model accounted for nonlinear properties of the ligamentous spine, wrapping of thoracic extensor muscles to take curved paths in flexion and trunk dynamic characteristics (inertia and damping) while subject to measured kinematics and gravity/external loads. A dynamic kinematics-driven approach was employed accounting for the spinal synergy by simultaneous consideration of passive structures and muscle forces under given posture and loads. Results satisfied kinematics and dynamic equilibrium conditions at all levels and directions. Net moments, muscle forces at different levels, passive (muscle or ligamentous) forces and internal compression/shear forces were larger in stoop lifts than in squat ones. These were due to significantly larger thorax, lumbar and pelvis rotations in stoop lifts. For the relatively slow lifting tasks performed in this study with the lowering and lifting phases each lasting approximately 2 s, the effect of inertia and damping was not, in general, important. Moreover, posterior shift in the position of the external load in stoop lift reaching the same lever arm with respect to the S1 as that in squat lift did not influence the conclusion of this study on the merits of squat lifts over stoop ones. Results, for the tasks considered, advocate squat lifting over stoop lifting as the technique of choice in reducing net moments, muscle forces and internal spinal loads (i.e., moment, compression and shear force).

Biomechanics of changes in lumbar posture in static lifting

STUDY DESIGN

In vivo measurements and model studies are combined to investigate the role of lumbar posture in static lifting tasks.

OBJECTIVES

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.

SUMMARY OF BACKGROUND DATA

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.

METHODS

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.

CONCLUSION

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.

Quantifying the lumbar flexion-relaxation phenomenon: theory, normative data, and clinical applications

STUDY DESIGN

A two-part investigation was conducted: 1) a prospective study of asymptomatic subjects quantitatively comparing trunk mobility to surface electromyographic (sEMG) signals from the erector spinae during trunk flexion; and 2) a prospective repeated-measures cohort study of patients with chronic disabled work-related spinal disorder tested for the flexion-relaxation (FR) phenomenon while measured simultaneously for lumbar spine inclinometric range of motion (ROM).

OBJECTIVES

To describe a theoretical model for the potential use of FR unloaded in assessing patients with chronic low back pain patients before and after rehabilitation, and to establish a normative database (Part 1) for subsequent use in comparison to patients with chronic low back pain (Part 2). The second part of the study assessed the clinical utility of combined sEMG and ROM measurements for assessing the FR phenomenon as a test to assist potentially in planning rehabilitation programs, guiding patients' individual rehabilitation progress, and identifying early posttreatment outcome failures.

SUMMARY OF BACKGROUND DATA

The FR phenomenon has been recognized since 1951, and it can be reproducibly assessed in normal subjects with FR unloaded. It can be found intermittently in patients with chronic low back pain. Recent studies have moved toward deriving formulas to identify FR, but only a few have examined a potential relation between inclinometric lumbar motion measures and the sEMG signal. No previous studies have developed normative data potentially useful for objectively assessing nonoperative treatment progress, effort, or the validity of permanent impairment rating measures.

METHODS

In Part 1, 12 asymptomatic subjects were evaluated in an intra- and interrater repeated-measures protocol to examine reliability of sEMG signal readings in FR, as well as ROM measures at FR and maximum voluntary flexion. The mean sEMG signal averaging right-left electrode recordings, as well as the gross, true, and sacral lumbar ROM measurements, were recorded as normative data. In Part 2, 54 patients with chronic disabled work-related spinal disorder referred as candidates for tertiary functional restoration rehabilitation participated in a standardized assessment protocol for sEMG and ROM measurement before rehabilitation. Those who completed the program were retested with the identical methodology after rehabilitation (n = 34) using the empirically derived cutoff scores for sEMG readings at FR and ROM from Part 1 and prior scientific literature. Pain disability self-reported scores were correlated with sEMG and ROM. Sensitivity and specificity of the sEMG for identifying abnormal motion were assessed.

RESULTS

In Part 1, the ability of the experienced testers to measure ROM and sEMG reliably at FR was high (r >or= 0.92; P < 0.001). All asymptomatic subjects achieved FR at a tightly clustered range of mean sEMG signals from 1 to 2.3 microV. Most of the variation between motion at FR and maximum voluntary flexion occurred through the hip (sacral) motion component of the gross (or total) motion measured at T12. In Part 2, posttreatment reliability for ROM, sEMG, and the ability to detect the FR point was high (r >or= 0.82; P < 0.001). More than 30% of the 54 patients tested before treatment demonstrated ability to achieve FR, with FR usually associated with higher ROM than in the non-FR patients. After treatment, 94% of those who completed the program achieved FR, including all those who achieved FR before treatment. Flexion-relaxation was associated with major improvement in ROM and pain disability self-report.

CONCLUSIONS

Flexion-relaxation measures a point at which true lumbar flexion ROM approaches its maximum in asymptomatic subjects. This also is the point at which lumbar extensor muscle contraction relaxes, allowing the lumbar spine to hang on its posterior ligaments. The gluteal and hamstring muscles then lower the flexed trunk even further by allowing the pelvis to rotate around the hips. This phenomenon was subsequently found in Part 2 to offer a potentially promising method for individualizing rehabilitation treatment, decreasing unnecessary utilization, identifying potential postrehabilitation treatment failures, and assessing permanent impairment rating validity. Moreover, this is the first study to demonstrate systematically that an absence of FR in patients with chronic low back pain can be corrected with treatment.

Effects of load and speed on lumbar vertebral kinematics during lifting motions

This experimental study investigated the effects of load magnitude and movement speed on lumbar vertebral kinematics during lifting task performance. Ten participants performed sagittally symmetric lifting movements with systematically varied load using either a normal or a faster-than-normal speed. Skin-surface markers were strategically placed over the participants' spinous processes and other landmarks representing major body joints and were recorded during the movements by a motion capture system. The center of rotation (COR) locations and segmental movement profiles for lumbar vertebrae L2 to L5 were derived and analyzed. Results suggested that (a) the COR locations and vertebral angular displacement were not significantly affected by the speed or load variation; (b) a faster speed tended to shorten the time to complete the acceleration for all the lumbar vertebrae considered; and (c) the load increase incurred a tendency for the L5 to complete the primary displacement in a briefer time while enduring greater peak acceleration and velocity. The findings lead to a better understanding of the relation between lifting dynamics and spinal motion. Potential applications of this research include the development of more accurate biomechanical models and software tools for depicting spinal motions and quantifying low-back stress.

Electromyographic activity of the trunk extensor muscles: effect of varying hip position and lumbar posture during Roman chair exercise

OBJECTIVE

To evaluate the effect of hip position and lumbar posture on the surface electromyographic activity of the trunk extensors during Roman chair exercise.

DESIGN

Descriptive, repeated measures.

SETTING

University-based musculoskeletal research laboratory.

PARTICIPANTS

Twelve healthy volunteers (7 men, 5 women; age range, 18-35y) without a history of low back pain were recruited from a university setting.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Surface electromyographic activity was recorded from the lumbar extensor, gluteal, and hamstring musculature during dynamic Roman chair exercise. For each muscle group, electromyographic activity (mV/rep) was compared among exercises with internal hip rotation and external hip rotation and among exercises by using a typical lumbar posture (nonbiphasic) and a posture that accentuated lumbar lordosis (biphasic).

RESULTS

For the lumbar extensors, electromyographic activity during exercise was 18% greater with internal hip rotation than external hip rotation (P< or =.05) and was 25% greater with a biphasic posture than with a nonbiphasic posture (P< or =.05). For the gluteals and hamstrings, there was no difference in electromyographic activity between internal and external hip rotation or between biphasic and nonbiphasic postures (P >.05).

CONCLUSION

The level of recruitment of the lumbar extensors can be modified during Roman chair exercise by altering hip position and lumbar posture. Clinicians can use these data to develop progressive exercise protocols for the lumbar extensors with a variety of resistance levels without the need for complex equipment.

Examination of the flexion relaxation phenomenon in erector spinae muscles during short duration slumped sitting

OBJECTIVE

The purpose of this study was to examine the myoelectric activity of the erector spinae muscles of the back in order to determine if the flexion relaxation phenomenon occurs in seated forward flexion or slumped postures.

BACKGROUND

The flexion relaxation phenomenon during standing forward flexion is well documented. However, flexion relaxation in seated forward flexion has not been studied. It is possible that flexion relaxation could be linked with low back pain that some individuals experience during seated work.

METHODS

Twenty-two healthy subjects (11 males, 11 females) participated in the study. Surface electromyography was used to measure the level of muscle activity at the thoracic and lumbar levels of the erector spinae muscles. An electromagnetic tracking device measured the three-dimensional movement of the lumbar spine. Five trials each of standing and seated forward flexion were performed.

RESULTS

A slumped sitting posture yielded flexion relaxation of the thoracic erector spinae muscles, whereas the lumbar erector spinae muscle group remained at relatively constant activation levels regardless of seated posture. Thoracic erector spinae silence occurred at a smaller angle of lumbar flexion during sitting than the flexion relaxation angle observed during standing flexion relaxation.

CONCLUSIONS

Since the myoelectric activity of the lumbar erector spinae did not increase, it is likely that the passive tissues of the vertebral column were loaded to support the moment at L4/L5. Ligaments contain a large number of free nerve endings which act as pain receptors and therefore could be a potential source of low back pain during seated work.

RELEVANCE

Examination of flexion relaxation during seated postures may provide insight into the association between low back pain and seated work.

Delayed-Onset Muscle Soreness Does Not Alter the Kinematics and Kinetics of the Squat-Lifting Technique

Context:

Little research has been done evaluating the effects of muscle soreness on a lifting task.

Objective:

To examine the effects of delayed-onset muscle soreness (DOMS) in the thigh musculature on kinematic and kinetic variables associated with the squat-lifting technique.

Design:

Pretest–posttest repeated measures, with treatment as the independent variable (DOMS and no DOMS of the thigh musculature).

Setting:

Research laboratory.

Participants:

Twenty healthy college students.

Intervention:

Subjects were videotaped lifting a 157-N crate before and after DOMS inducement.

Main Outcome Measures:

A 2-dimensional sagittal-plane video analysis was used to calculate 7 kinematic and kinetic variables.

Results:

DOMS had no effect on L5/S1 torque and shear or compression, hip torque and range of motion, or knee torque and range of motion during lifting.

Conclusions:

DOMS does not appear to alter kinematic and kinetic variables associated with the squat-lifting technique.

Regressionally determined vertebral inclination angles of the lumbar spine in static lifts

OBJECTIVE

Our previous study has developed the non-invasive models to predict the vertebral inclination angles by relating the external stick marker angles and radiographic measurements during trunk flexion. Based on these models, the present study attempted to further predict the inclination angles using externally measured body posture (i.e., lumbar posture, trunk flexion angle, knee angle) as well as load handling.

DESIGN

Prediction models of the vertebral inclination angles were developed with a stepwise regression technique. This was done by selecting related postural variables as well as load handling as predictors.

BACKGROUND

The technique of skin-surface stick marker has been investigated for measuring vertebral inclination angles. This technique, however, is rarely systematically validated by radiographic measurement because of concerns over radiation exposure, especially for ergonomical purposes.

METHODS

Twelve healthy men aged 22-31 years were recruited in the experiment. The angles of the vertebral markers and subject's posture were recorded videographically as the subject performed a given task. Prediction models were then developed to express the relationships between the vertebral inclinations and the lifting postures.

RESULTS

The prediction models revealed that the lumbar posture (lordosis or kyphosis) had a statistically significant effect on these inclination angles. Non-linear first-order regression models of the torso angle and the pelvic angle were fit to the transformed vertebral inclination angles (transformed from external stick marker angle), with resulting R(2) values between 0. 86 and 0.92.

CONCLUSIONS

These findings indicate that the vertebral inclination angles can be calculated easily and with relative accuracy on the basis of the externally measured torso and pelvis angles.

RELEVANCE

Measurements of lumbosacral vertebral inclination angles are important in assessing low back stress during lifting. In this study, we used a regression approach to model these angles of the lumbar/sacrum spine in different lumbar postures in the sagittal plane. Our data suggest that the vertebral inclination angles can be calculated easily. These models may be useful to the low back stress evaluation and job design through a biomechanical analysis.

Predicting the vertebral inclination of the lumbar spine

The objectives of this study were to examine the accuracy of the external stick marker method in the assessment of sagittal plane vertebral inclination (L1 to S1) during trunk flexion and to develop regression equations for predicting vertebral inclinations of the lumbar spine. Lateral radiographs of 16 subjects were taken from the upright position to a trunk flexion of 90 degrees, in 30 degrees increments. Each subject was radiographed in only three of the four torso positions to minimize the risks of radiation. The inclinations of the vertebrae in the radiographic view were then obtained. The results show that the stick marker technique is a poor protocol for measuring vertebral inclination of the lumbar spine. During trunk flexion, the upper vertebrae incline linearly and the lower vertebrae incline exponentially. This is verified by the finding that the best-fit equations selected by regression techniques were linear at the upper vertebrae (L1, L2 and L3) and non-linear at the lower ones (L4, L5 and S1), with a mean R2 value of 0.964. The inherent difference in motion pattern between the vertebrae of the lumbar spine during trunk flexion is discussed for clinical and ergonomic purposes.

Metabolic and cardiorespiratory responses to continuous box lifting and lowering in nonimpaired subjects

STUDY DESIGN

A within-subject experimental design.

OBJECTIVES

To compare the magnitude of metabolic and cardiorespiratory changes produced during box lifting and lowering among combinations of lift technique (leg lift and leg-torso lift) and lift weight (10.8 and 15.4 kg).

BACKGROUND

Continuous box lifting and lowering can be used as an exercise in a low-back rehabilitation program. Awareness of the possible cardiovascular stress of this activity is important to the clinician because some patients may have existing cardiovascular pathologies or possess unknown risk factors for cardiovascular disease.

METHODS AND MEASURES

A group of 17 nonimpaired men 26 +/- 8 years of age (mean +/- SD) performed the 4 experimental trials on different days in a counterbalanced order determined by a Latin Square design. Lifting and lowering was performed for 6 continuous minutes at a rate of 12 cycles per minute. Physiologic variables were oxygen uptake, minute ventilation, heart rate, systolic blood pressure, diastolic blood pressure, metabolic equivalent, and rate-pressure product.

RESULTS

There were stepwise increases in the values for oxygen uptake, minute ventilation, heart rate, metabolic equivalent, and rate-pressure product from the leg-torso lift to the leg lift and from 10.8 to 15.4 kg of weight within each lift technique (with the exception that minute ventilation and heart rate did not differ between the leg-torso lift at 15.4 kg and the leg lift at 10.8 kg). For the 4 lifts, values (mean +/- SD) varied from 20.3 +/- 5.4 to 28.8 +/- 5.8 mL x kg x min(-1) for oxygen uptake, 42.2 +/- 11.1 to 66.4 +/- 15.2 L x min(-2) for minute ventilation,129 +/- 20.6 to 156 +/- 16.5 beats x min(-1) for heart rate, 5.8 +/- 1.6 to 8.2 +/- 1.6 for metabolic equivalent, and 197 +/- 49.4 to 245 +/- 41.2 for rate-pressure product (x10(-2)).

CONCLUSION

The leg lift with the 15.4-kg weight produced the greatest physiologic stress. Because of the magnitude of the increase in the variables measured for all 4 types of lifts, clinicians should closely monitor patients' response to this type of exercise.

Relationship between lifting capacity and anthropometric measures

STUDY DESIGN

Prospective analysis of relationship between lifting capacity and multiple anthropometric variables.

OBJECTIVES

To determine the relationship between lifting capacity and anthropometric variables and to model this relationship quantitatively.

BACKGROUND

Low-back injuries commonly occur in individuals who perform lifting tasks. Objective data are needed to determine preinjury lifting capacity that, in turn, might be used to guide decisions during rehabilitation of these injuries.

METHODS AND MEASURES

We recorded age and sex and measured the following variables for 35 men and 23 women between the ages of 22 and 40: height, weight, percentage of body fat, torso height, pelvic width, pelvic girth, arm length, thigh girth, and calf girth. Variables were selected for the study on the basis of theoretical modeling or previous research regarding the relationship between study variables and lifting capacity. Subjects also were tested to determine their maximum lifting capacity by using a lordotic lumbar spine lifting technique.

RESULTS

Stepwise regression analysis indicated that the combination of sex, age, thigh girth, pelvic girth, and percentage body fat was significantly related to maximum lift capacity (multiple R2 = 0.76). The mean absolute difference (+/- SD) between lifted amount predicted by the regression model and the actual amount lifted was 118.6 +/- 86 N (26 +/- 19.3 lb), which corresponded to an average absolute error of 16% (SD = 14%) of the actual weight lifted.

CONCLUSION

The results may be useful in estimating 1 aspect of preinjury lifting capacity. Similar studies are needed to model the requirements of frequency of lift, duration of lifting efforts, variety of hand-object coupling, and combined lifting and reaching.

A comparison of trunk extensor strength and squat lifting ability

Back testing devices are frequently utilized in the clinic to assess function and return to work readiness in place of the job task, yet little research on their validity has been reported. This study was conducted to determine if correlations exist between squat lifting and isoinertial and isometric trunk extensor strength, torso length and isoinertial and isometric trunk extensor strength, and body weight and isoinertial and isometric trunk extensor strength. Twenty-eight subjects participated in two sessions involving B200 testing and 30.5 cm to knuckle lifting ability. Regression and correlations were performed. The results indicate that body weight and torso length do not demonstrate a relationship with trunk extensor strength, and isometric and isoinertial trunk extensor strength cannot be used accurately to estimate one's 30.5 cm to knuckle lifting ability. In conclusion, other anthropometric measures should be investigated if anthropometrics are used to estimate strength, and functional testing should be used to evaluate function.

Soft system stabilization of the lumbar spine as an alternative surgical modality to lumbar arthrodesis in the facet syndrome. Preliminary results

The authors present preliminary results in a series of 27 patients with a lumbar and/or lumbosacral facet syndrome operated on by use of the soft-system-Stabilization (SSS) according to Graf. Attention is paid to the correct selection of patients for this surgical technique. Excellent, good, satisfactory, moderate, and poor results were obtained in 19 (70%), 2 (7.5%), 5 (18.5%), 1 (3.5%), and 0 instances, respectively. The authors think that a Graf-procedure may be indicated in young to middle-aged patients with a lumbar and/or lumbosacral facet syndrome with 1.) no arthrotic changes of the facet joints, 2.) a still intact disc and/or only mild loss of intervertebral distance, 3.) well trained low-back muscles, and 4.) a clear-cut pain relief on test-anaesthesia of articular nerves and trial immobilization in a plastic jacket.

Flexion relaxation during lifting: implications for torque production by muscle activity and tissue strain at the lumbo-sacral joint

During the full flexion phase of the back lift movement the lumbar part of the erector spinae muscle exhibits a reduced activity level (flexion relaxation). This study addresses the question how the required extension torque in the lumbo-sacral joint (L5/S1 joint) is balanced during the period in which apparently the lumbar erector spinae ceases to take its share. Six subjects participated in the experiment in which they performed seven lifting tasks. The load, the range of movement, and the phase in which the load was handled (lifting or lowering) were varied. A dynamic linked segment model was applied to determine the momentary torques acting at the L5/S1 joint, while the EMGs of the lumbar and thoracic part of the erector spinae muscle were measured. Furthermore, the lengths between markers on the lumbar and thoracic part of the trunk were determined to reveal changes in length during the movement. The dynamic EMGs were normalized to trunk angle-dependent maximal levels. The L5/S1 joint torques were analysed and combined with the normalized EMG data and the kinematics of the trunk, which are assumed to indicate the elongation of passive tissues. Although in the normalization procedure the change of the length-force relationship of the erector spinae was taken into account, the dynamic lumbar EMG activity decreased to a low-activity level (the phenomenon of flexion relaxation). This coincided with a 25% increase in lumbar length suggesting that passive tissue strain provided part of the required extension torque. In the tasks where a barbell was handled a significant increase in EMG level of the thoracic part of the erector spinae occurred just before the flexion relaxation at the lumbar level. Apparently, the extensor function of the lumbar part is then taken over by the thoracic part of the erector spinae muscle. This suggests that an intricate coordinating mechanism is operative that apportions the load to be balanced over active--(lumbar and thoracic part of the erector spinae) and passive structures (post vertebral ligaments).

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.