Anterior-posterior Shear Forces Research Articles

Kinetics of Badminton Lunges in Four Directions

The lunge is the most fundamental skill in badminton competitions. Fifteen university-level male badminton players performed lunge maneuvers in four directions, namely, right-forward, left-forward, right-backward, and left-backward, while wearing two different brands of badminton shoes. The test compared the kinetics of badminton shoes in performing typical lunge maneuvers. A force plate and an insole measurement system measured the ground reaction forces and plantar pressures. These measurements were compared across all lunge maneuvers. The left-forward lunge generated significantly higher first vertical impact force (2.34 ± 0.52 BW) than that of the right-backward (2.06 ± 0.60 BW) and left-backward lunges (1.78 ± 0.44 BW); higher second vertical impact force (2.44 ± 0.51 BW) than that of the left-backward lunge (2.07 ± 0.38 BW); and higher maximum anterior-posterior shear force (1.48 ± 0.36 BW) than that of the left-backward lunge (1.18 ± 0.38 BW). Compared with other lunge directions, the left-forward lunge showed higher mean maximum vertical impact anterior-posterior shear forces and their respective maximum loading rates, and the plantar pressure at the total foot and heel regions. Therefore, the left-forward lunge is a critical maneuver for badminton biomechanics and related footwear research because of the high loading magnitude generated during heel impact.

Relative performances of artificial neural network and regression mapping tools in evaluation of spinal loads and muscle forces during static lifting

Two artificial neural networks (ANNs) are constructed, trained, and tested to map inputs of a complex trunk finite element (FE) model to its outputs for spinal loads and muscle forces. Five input variables (thorax flexion angle, load magnitude, its anterior and lateral positions, load handling technique, i.e., one- or two-handed static lifting) and four model outputs (L4–L5 and L5–S1 disc compression and anterior–posterior shear forces) for spinal loads and 76 model outputs (forces in individual trunk muscles) are considered. Moreover, full quadratic regression equations mapping input–outputs of the model developed here for muscle forces and previously for spine loads are used to compare the relative accuracy of these two mapping tools (ANN and regression equations). Results indicate that the ANNs are more accurate in mapping input–output relationships of the FE model (RMSE= 20.7N for spinal loads and RMSE= 4.7N for muscle forces) as compared to regression equations (RMSE= 120.4N for spinal loads and RMSE=43.2N for muscle forces). Quadratic regression equations map up to second order variations of outputs with inputs while ANNs capture higher order variations too. Despite satisfactory achievement in estimating overall muscle forces by the ANN, some inadequacies are noted including assigning force to antagonistic muscles with no activity in the optimization algorithm of the FE model or predicting slightly different forces in bilateral pair muscles in symmetric lifting activities. Using these user-friendly tools spine loads and trunk muscle forces during symmetric and asymmetric static lifts can be easily estimated.

Lumbo-pelvic loading during fast bowling in adolescent cricketers: The influence of bowling speed and technique

This study aimed to assess changes in bowling technique and lumbar load over the course of a bowling spell in adolescent fast bowlers, and to investigate the relationship between lumbar loads during fast bowling and kinematic factors which have previously been associated with low back injury. Three-dimensional motion analysis was carried out on forty participants who performed an 8-over bowling spell. There were no significant changes in bowling technique or lumbar loads over the course of the spell. Bowling with a more extended front knee, faster ball release speed and increased shoulder counter-rotation were related to increased lumbo-pelvic loading – in particular peak transverse plane rotation moments and anterior-posterior shear forces. These lumbar loads may be a factor in low back injury aetiology and future studies should investigate the relationship between lumbar loading, injury incidence and other risk factors.

A Musculoskeletal Modeling Approach for Estimating Anterior Cruciate Ligament Strains and Knee Anterior–Posterior Shear Forces in Stop-Jumps Performed by Young Recreational Female Athletes

The central goal of this study was to contribute to the advancements being made in determining the underlying causes of anterior cruciate ligament (ACL) injuries. ACL injuries are frequently incurred by recreational and professional young female athletes during non-contact impact activities in sports like volleyball and basketball. This musculoskeletal-neuromuscular study investigated stop-jumps and factors related to ACL injury like knee valgus and internal-external moment loads, knee anterior-posterior (AP) shear forces, ACL strains and internal forces. Motion capture data was obtained from the landing phase of stop-jumps performed by eleven young recreational female athletes and electromyography (EMG) data collected from quadriceps, hamstring and gastrocnimius muscles which were then compared to numerically estimated activations. Numerical simulation tools used were Inverse Kinematics, Computed Muscle Control and Forward Dynamics and the knee modeled as a six degree of freedom joint. Results showed averaged peak strains of 12.2±4.1% in the right and 11.9±3.0% in the left ACL. Averaged peak knee AP shear forces were 482.3±65.7N for the right and 430.0±52.4N for the left knees, approximately equal to 0.7-0.8 times body weight across both knees. A lack of symmetry was observed between the knees for valgus angles (p<0.04), valgus moments (p<0.001) and muscle activations (p<0.001), all of which can be detrimental to ACL stability during impact activities. Comparisons between recorded EMG data and estimated muscle activations show the relation between electrical signal and muscle depolarization. In summary, this study outlines a musculoskeletal simulation approach that provides numerical estimations for a number of variables associated with ACL injuries in female athletes performing stop-jumps.

Design and biomechanical evaluation of a rodent spinal fixation device

Structured Study DesignAn in vitro and in vivo study in rats.ObjectivesTo design a novel rat spinal fixation device and investigate its biomechanical effectiveness in stabilizing the spine up to eight weeks post injury.MethodsA fixation device made of polyetheretherketone was designed to stabilize the spine via bilateral clamping pieces. The device effectiveness was assessed in a Sprague-Dawley rat model after it was applied to a spine with a fracture-dislocation injury produced at C5–C6. Animals were euthanized either immediately (n=6) or eight weeks (n=9) post-injury and the C3-T1 segment of the cervical spine was removed for biomechanical evaluation. Segments of intact spinal columns (C3-T1) (n=6) served as uninjured controls. In these tests, anterior-posterior shear forces were applied to the C3 vertebra to produce flexion and extension bending moments at the injury site (peak 12.8Nmm). The resultant two-dimensional motions at the injury site (i.e. C5–C6) were measured using digital imaging and reported as ranges of motion (ROM) or neutral zones (NZ).ResultsFlexion/extension ROMs (average ± S.D.) were 18.1 ± 3.3°, 19.9 ± 7.5°, and 1.5 ± 0.7°, respectively for the intact, injured/fixed, and injured/8-week groups, with the differences being highly significant for the injured/8-week group (p=0.0002). Flexion/extension NZs were 3.4 ± 2.8°, 5.0 ± 2.4°, and 0.7 ± 0.5°, respectively for the intact, injured/fixed, and injured/8-week groups, with the differences being significant for the injured/8-week group (p =0.04).ConclusionThe device acutely stabilizes the spine and promotes fusion at the site of injury.

Vertical torque responses to vestibular stimulation in standing humans

The effects of electrical vestibular stimulation upon movement and perception suggest two evoked sensations: head roll and inter-aural linear acceleration. The head roll vector causes walking subjects to turn in a direction dependent on head pitch, requiring generation of torque around a vertical axis. Here the effect of vestibular stimulation upon vertical torque (T(z)) was investigated during quiet stance. With the head tilted forward, square-wave stimuli applied to the mastoid processes evoked a polarity-specific T(z) response accompanied by trunk yaw. Stochastic vestibular stimulation (SVS) was used to investigate the effect of head pitch with greater precision; the SVS–T(z) cross-correlation displayed a modulation pattern consistent with the head roll vector and this was also reflected by changes in coherence at 2–3 Hz. However, a separate response at 7–8 Hz was unaffected by head pitch. Head translation (rather than rotation) had no effect upon this high frequency response either, suggesting it is not caused by a sense of body rotation induced by an inter-aural acceleration vector offset from the body. Instead, high coherence between medio-lateral shear force and T(z) at the same frequency range suggests it is caused by mechanical coupling to evoked medio-lateral sway. Consistent with this explanation, the 7–8 Hz response was attenuated by 90 deg head roll or yaw, both of which uncouple the inter-aural axis from the medio-lateral sway axis. These results demonstrate two vertical torque responses to electrical vestibular stimulation in standing subjects. The high frequency response can be attributed to mechanical coupling to evoked medio-lateral sway. The low frequency response is consistent with a reaction to a sensation of head roll, and provides a novel method for investigating proprioceptive-vestibular interactions during stance.

Derivation of Clinically Relevant Boundary Conditions Suitable for Evaluation of Chronic Impingement of Lumbar Total Disk Replacement: Application to Standard Development

Abstract Currently available standardized methods for evaluating the long-term wear of total disk replacements do not incorporate the effects of potential device impingement. Creation of a standard that incorporates device impingement is difficult without a thorough understanding of the associated biomechanical environment. Arbitrary modification of the currently available wear-test protocols to account for device impingement may add unnecessary cost, and potentially inaccurate, unrealistic results. Finite element models provide the ability to control variation and test for a wide range of parameters without the excessive time and monetary costs associated with cadaveric testing or wear simulations. However, careful validation and verification of these models is required in order to ensure predictability. Retrieved implants can be used to validate the clinical predictability of finite element models (FEMs). The objective of the current study was to quantify the ability of a previously developed FEM of the lumbar spine to predict polyethylene damage modes and impingement in actual clinical scenarios, and extract the loading and boundary conditions for implementation into a new lumbar TDR wear simulation standard. In order to achieve this objective, actual clinical scenarios, associated with retrieved implants, were modeled and simulated. We hypothesized that clinical damage modes, including both impingement and non-impingement scenarios, can be predicted using a FEM that incorporates case-specific clinical factors, anterior-posterior shear forces, coupled translations, and facet contact.

Predictive equations to estimate spinal loads in symmetric lifting tasks

Response surface methodology is used to establish robust and user-friendly predictive equations that relate responses of a complex detailed trunk finite element biomechanical model to its input variables during sagittal symmetric static lifting activities. Four input variables (thorax flexion angle, lumbar/pelvis ratio, load magnitude, and load position) and four model responses (L4–L5 and L5–S1 disc compression and anterior–posterior shear forces) are considered. Full factorial design of experiments accounting for all combinations of input levels is employed. Quadratic predictive equations for the spinal loads at the L4–S1 disc mid-heights are obtained by regression analysis with adequate goodness-of-fit ( R 2>98%, p<0.05, and low root-mean-squared-error values compared with the range of predicted spine loads). Results indicate that intradiscal pressure values at the L4–L5 disc estimated based on the predictive equations are in close agreement with available in vivo data measured under similar loadings and postures. Combinations of input (posture and loading) variable levels that yield spine loads beyond the tolerance compression limit of 3400 N are identified using contour plots. Ergonomists and bioengineers, faced with the dilemma of using either complex but more accurate models on one hand or less accurate but simple models on the other hand, have thereby easy-to-use predictive equations that quantifies spinal loads and risk of injury under different occupational tasks of interest.

Pure moment testing for spinal biomechanics applications: Fixed versus sliding ring cable-driven test designs

In vitro multi-axial bending testing using pure moment loading conditions has become the standard in evaluating the effects of different types of surgical intervention on spinal kinematics. Simple, cable-driven experimental set-ups have been widely adopted because they require little infrastructure. Traditionally, “fixed ring” cable-driven experimental designs have been used; however, there have been concerns with the validity of this set-up in applying pure moment loading. This study involved directly comparing the loading state induced by a traditional “fixed ring” apparatus versus a novel “sliding ring” approach. Flexion-extension bending was performed on an artificial spine model and a single cadaveric test specimen, and the applied loading conditions to the specimen were measured with an in-line multiaxial load cell. The results showed that the fixed ring system applies flexion-extension moments that are 50–60% less than the intended values. This design also imposes non-trivial anterior–posterior shear forces, and non-uniform loading conditions were induced along the length of the specimen. The results of this study indicate that fixed ring systems have the potential to deviate from a pure moment loading state and that our novel sliding ring modification corrects this error in the original test design. This suggests that the proposed sliding ring design should be used for future in vitro spine biomechanics studies involving a cable-driven pure moment apparatus.

Development of a piezoelectric polymer film sensor for plantar normal and shear stress measurements

We have developed a new sensor prototype for plantar pressure measurements during gait. The mechanical stress at the plantar surface has two components, pressure acting normal to the surface and shear stress acting tangential to the surface. The shear stress can be further divided into anterior–posterior (AP) and medial–lateral (ML) components. The developed sensor simultaneously measures both normal and shear stresses. It utilizes commercial polyvinylidenefluoride (PVDF) material and consists of four separate sensor elements. This paper presents the sensor development and calibration for each force components. A shaker providing dynamic excitation force was used in the calibration. Average sensitivities computed from the results were (12.6 ± 0.8) mV/N for the normal force, (223.9 ± 20.3) mV/N for the AP shear force and (55.2 ± 11.9) mV/N for the ML shear force. A preliminary plantar pressure measurement was also done. The results obtained were promising. However, the sensor developed here is the first prototype. In future, a matrix sensor based on this principle is planned to be constructed.

Effect of lifting height and load mass on low back loading

The objective of this study was to quantify the effect of lifting height and mass lifted on the peak low back load in terms of net moments, compression forces and anterior–posterior shear forces. Ten participants had to lift a box using four handle heights. Low back loading was quantified using a dynamic 3-D linked segment model and a detailed electromyographic driven model of the trunk musculature. The effects of lifting height and lifting mass were quantified using a regression technique (GEE) for correlated data. Results indicate that an increase in lifting height and a decrease in lifting mass were related to a decrease in low back load. It is argued that trunk flexion is a major contributor to low back load. For ergonomic interventions it can be advised to prioritise optimisation of the vertical location of the load to be lifted rather than decreasing the mass of the load for handle heights between 32 cm and 155 cm, and for load masses between 7.5 and 15 kg. Lifting height and load mass are important determinants of low back load during manual materials handling. This paper provides the quantitative effect of lifting height and mass lifted, the results of which can be used by ergonomists at the workplace to evaluate interventions regarding lifting height and load mass.

Landing Mechanics Between Non-injured Women and Women with ACL Reconstruction During a 40-cm Drop Jump

Women with ACL reconstruction present with neuromuscular deficits that could predispose them to further injuries during sports participation. PURPOSE: To compare landing mechanics during a 40-cm drop jump and a 20-cm up-down hop tasks between ACL reconstructed and non-injured women. METHODS: Fourteen women with ACL reconstruction (25.4 ± 3.1) and fifteen non-injured women (24.6 ± 2.6) participated in this study. Each participant had 12 retro-reflective markers attached over bony prominences on one lower extremity and surface EMG electrodes in the gluteus maximus, quadriceps, and hamstrings. Each participant performed five drop jump task trials and 2 trials of the up-down hop task after a warm-up protocol. The drop jump consisted of standing on a 40-cm platform and performing a maximal vertical jump after landing onto a force plate. The up-down consisted of jumping single-legged ten times up-to and down-from a 20-cm step. Peak kinematics, kinetics, normalized rectified electromyography measures and quadriceps/hamstrings co-contraction ratio were analyzed after normality assumptions and outliers screening procedures. Multivariate analyses of variance, with follow-up ANOVA's, were used for analyses. RESULTS: During the drop jump, no statistically significant differences between groups were found for peak hip and knee joint angles. However, significant differences between groups were found for kinetic and EMG variables. Follow-up ANOVA's on kinetic and EMG variables showed lower peak anterior-posterior shear forces, greater joint moments, greater quadriceps/hamstrings co-contraction ratios, greater gluteus maximus EMG and greater rectus femoris EMG in the group with ACL reconstruction. During the up-down, no statistically significant differences were found for any of the variables measured. CONCLUSIONS: Landing mechanics were similar between healthy, non-injured women and women more than one year after ACL reconstruction. During the drop jump, electromyographic measures suggested neuromuscular compensation strategies in women with ACL reconstruction that could explain the similarities in landing kinematics. However, differences for kinetic measures suggested differences in landing strategies that could predispose women with ACL reconstruction to further injury.

Dynamic loading performance of fasciocutaneous flaps and implications for gait

Recent advancements in microsurgery allow the free tissue transfer for reconstruction of soft-tissue defects on the plantar surface of the foot. Fasciocutaneous flaps are one available option to the reconstructive surgeon. However, their functional weight-bearing capabilities have never been adequately evaluated. This study investigated the dynamic loading performance of selected fasciocutaneous flaps during walking using instrumented gait analysis. We investigated 6 feet with reconstructed heels along with their contralateral normal feet. A control group of normals was included also. Time-distance, ground reaction force parameters and plantar foot pressure distribution were evaluated. Data were normalized to account for anthropometric variations. A series of t-tests were used to investigate contrasts. Walking velocity of injured subjects was decreased (P<0.0001). Step length and single limb support were the shortest for the involved feet (P<0.04). Double limb support and swing were the longest (P<0.0002). The reconstructed heels sustained high pressures (P<0.05) and vertical loadings underlining their functional weight-bearing capabilities. However, the walking patterns implemented by the injured subjects resulted in reduced anterior-posterior shear forces that could help maintain the integrity of the shear plane at the graft-recipient bed interface. The dynamic loading capabilities of the fasciocutaneous flaps make it an effective means for restoring functional gait. Patients implement gait patterns that result in primarily decreasing shear forces. Consequently, the fasciocutaneous flaps should be included in the surgeons' armentarium as a plausible reconstructive means for soft-tissue defects on the plantar surface of the foot.

Muskuloskeletale Belastungen im Schafshinterlauf: Mechanische Rahmenbedingungen der Heilung

Although the sheep is a standard model for the analysis of biological healing processes after surgical intervention at the knee and shank, the in vivo tibio-femoral joint contact forces and the resulting musculoskeletal loading conditions have yet to be studied in detail.The three-dimensional kinematics of three Merino-mix sheep right hind limbs were recorded using reflective markers that were attached to Schanz’ screws, firmly anchored in the bone. This motion data was used together with the simultaneously measured external loading (ground reaction forces) to calculate the muscle and joint contact forces, as well as the internal loads within the bones. Whilst the motion mainly occurred in the sagittal plane, significant out of plane motion was observed, especially at the hip and knee joint (ab/adduction hip: 13°, knee: 10°; internal/external rotation hip: 12°, knee: 14°). The axial component of the tibio-femoral contact force was 2.1 times body weight (BW). The medio-lateral and anterior-posterior shear forces amounted to only 0.7 times BW. The loading in the diaphysis of the tibia under physiological musculoskeletal conditions was mainly axial compression (0.89 BW) together with only small shear forces (0.15 BW). The results of the musculoskeletal analyses presented here add to the understanding of the mechanical loading conditions in sheep. This expanded knowledge aids in the interpretation

Comparison of Spinal Loads in Kneeling and Standing Postures during Manual Materials Handling

Kneeling in a restricted posture during manual materials handling has been associated with increased risk of low back pain. Little is known about the effect of kneeling posture on spinal loads. The purpose of this study was to compare differences in spinal loading between kneeling and standing postures for lifting tasks. Twelve subjects asymmetrically lifted luggage of three weights to three heights from floor while kneeling. Three subjects also performed the same tasks from waist height while standing. An adapted free-dynamic EMG-assisted biomechanical model was used to calculate spinal loads. Statistical analysis showed that there was no difference in compression between kneeling and standing (p=0.9605), but kneeling resulted in increased anterior-posterior and lateral shear forces on the lumbar spine (p =0.0002 and p&lt;0.0001, respectively). Spinal loading changes while kneeling in a restricted posture may increase the risk of low back injury and must be considered in ergonomic job design.

The Effect of a Variable Lumbar Erector Spinae Sagittal Plane Moment Arm on Predicted Spinal Loading

Recent research indicates that the sagittal plane moment arm of the erector spinae decreases at the L5/S1 level during torso flexion. The objective of this study was to assess the predicted L5/S1 spinal loading from a lifting task when allowing the erector spinae sagittal plane moment arm to vary during torso flexion. Nineteen male subjects lifted three loads from two origin locations to an upright neutral posture. Spinal loading was predicted from an EMG-assisted biomechanical model that allowed the erector spinae moment arm to vary during torso flexion. The predicted lateral, anterior-posterior shear and compression forces increased by 7.4%, 11.1% and 6.6%, respectively, when compared to using a biomechanical model that kept the erector spinae moment arm constant. These results suggest that models that account for the varying erector spinae moment arm predict greater spinal loads, especially for motions that involve a large degree of torso flexion.

The effect of weightbearing and external loading on anterior cruciate ligament strain

A force balance between the ligaments, articular contact, muscles and body weight maintains knee joint stability. Thus, it is important to study anterior cruciate ligament (ACL) biomechanics, in vivo, under weightbearing conditions. Our objective was to compare the ACL strain response under weightbearing and non-weightbearing conditions and in combination with three externally applied loadings: (1) anterior–posterior shear forces, (2) internal–external torques, and (3) varus–valgus moments. A strain transducer was implanted on the ACL of 11 subjects. All joint loadings were performed with the knee at 20° of flexion. A significant increase in ACL strain was observed as the knee made the transition from non-weightbearing to weightbearing. During anterior shear loading, the strain values produced during weightbearing were greater than those of the non-weightbearing knee (shear loads <40 N). At higher shear loads, the strain values became equal. During axial torsion, an internal torque of 10 Nm strained the ACL when the knee was non-weightbearing while an equivalent external torque did not. Weightbearing significantly increased ACL strain values in comparison to non-weightbearing with the application of external torques and low internal torques (<3 Nm). The strains became equal for higher internal torques. For V–V loading, the ACL was not strained in the non-weightbearing knee. However, weightbearing increased the ACL strain values over the range of moments tested. These data have important clinical ramifications in the development of rehabilitation protocols following ACL reconstruction since weightbearing has been previously thought to provide a protective mechanism to the healing graft.

Knee joint loading in forward versus backward pedaling: implications for rehabilitation strategies

Objective. To use forward dynamic simulations of forward and backward pedaling in order to determine whether backward pedaling offers theoretical advantages over forward pedaling to rehabilitate common knee disorders. Design. A comparison of knee joint loads was performed during forward and backward pedaling. Background. Pedaling has been shown to be an effective rehabilitation exercise for a variety of knee disorders. Recently, backward gait has been shown to produce greater knee extensor moments and reduced patellofemoral joint loads compared to forward gait. But to date, no study has examined the efficacy of backward pedaling as a safe alternative to forward pedaling in rehabilitation programs. Methods. A musculoskeletal model and optimization framework was used to generate simulations of forward and backward pedaling. Tibiofemoral and patellofemoral joint reaction forces were quantified. Results. Lower tibiofemoral compressive loads, but higher patellofemoral compressive loads, were observed in backward pedaling. Lower protective anterior–posterior shear force was observed in backward pedaling near peak extension. Conclusions. Backward pedaling offers reduced tibiofemoral compressive loads for those patients with knee disorders such as menisci damage and osteoarthritis, but higher patellofemoral compressive loads. Therefore, backward pedaling is not recommended for patients experiencing patellofemoral pain. Further, backward pedaling should not be recommended after anterior cruciate ligament injury or reconstruction. Relevance The results of this study indicate that the design of rehabilitation programs including pedaling exercises should be injury specific with particular attention paid to the mechanics of the task.

Biomechanical analysis of materials handling manipulators in short distance transfers of moderate mass objects: joint strength, spine forces and muscular antagonism

Although often suggested as a control measure to alleviate musculoskeletal stresses, the use of mechanical assistance devices (i.e. manipulators) in load transfers has not been extensively studied. Without data describing the biomechanical effects of such devices, justification for decisions regarding implementation of such tools is difficult. An experimental study of two types of mechanical manipulators (articulated arm and overhead hoist) was conducted to determine whether biomechanical stresses, and hence injury risk, would be alleviated. Short distance transfers of loads with moderate mass were performed both manually and with manipulator assistance under a variety of task conditions. Using analysis and output from new dynamic torso models, strength demands at the shoulders and low back, lumbar spine forces, and lumbar muscle antagonism were determined. Strength requirements decreased significantly at both the shoulders and low back when using either manipulator in comparison with similar transfers performed manually. Peak spine compression and anteriorposterior (a-p) shear forces were reduced by about 40% on average, and these reductions were shown to be primarily caused by decreases in hand forces and resultant spinal moments. Two metrics of muscular antagonism were defined, and analysis showed that torso muscle antagonism was largest overall when using the hoist. The results overall suggest that hoist-assisted transfers, although better in reducing spine compression forces, may impose relatively higher demands on coordination and/or stability at extreme heights or with torso twisting motions. The relatively higher strength requirements and spine compression associated with the articulated arm may be a result of the high inertia of the system. Potential benefits of practice and training are discussed, and conclusions regarding implementation of mechanical manipulators are given.

Evaluation of spinal loading during lowering and lifting

Objective. To estimate the three-dimensional spinal loads during various lifting and lowering tasks. Design. The in vivo measurements of the trunk dynamics, moments, and myoelectric activity were used as inputs into an electromyographic-assisted model used to predict the three-dimensional spinal loads. Background. Previous studies of eccentric motions have investigated muscle activity, trunk strength, and trunk moments. A void in the body of knowledge exists in that none of these studies investigated spinal loading. Methods. Ten subjects lifted (40 ° of flexion to 0 °) and lowered (0 ° of flexion to 40 °) boxes while positioned in a structure that restrained the pelvis and hips. The tasks were performed under isokinetic trunk velocities of 5, 10, 20, 40, and 80 deg s −1 while holding a box with weights of 9.1, 18.2, and 27.3 kg. Results. Lowering strength was found to be 56% greater than lifting strength. The lowering tasks produced significantly higher compression forces but lower anterior-posterior shear forces than the lifting tasks. The differences in the spinal loads produced by the two lifting tasks were attributed to differences in coactivity and unequal lifting moments (i.e. holding the box farther away from the body). Conclusions. The nature of the spinal loads that occur during lowering and lifting were significantly different. The difference in spinal loads may be explained by different lifting styles.