Maximum isometric trunk muscle strength and activity at trunk axial rotation during sitting

This study was performed to provide information relating to the twisted posture being characteristic of the driver of an agricultural tractor working in the field. The relationship of trunk axial strength and muscle activity to trunk twisting angle of prerotation was determined and quantified. Differences between tractor drivers and office workers, and between the two directions of twisting action were also studied. Nine male tractor drivers and nine male office workers performed isometric maximum efforts at about −40, −20, 0, 20 and 40° of pre-set trunk twisting angles in both the clockwise and counterclockwise directions. Exerted torque, true angle of prerotation and muscle activity from left and right side of each of obliquus externus, rectus abdominis and erector spinae were measured simultaneously. The results showed that the subjects could exert the greatest torques when being prerotated in the opposite direction and the lowest torques when being prerotated in the same direction to the direction of exertion. The exerted torques were within the range of 65 – 145 Nm. There were large differences in obliquus externus and erector spinae activity due to the twisting direction. There were also changes in muscle activity from obliquus externus and rectus abdominis due to prerotation angle. The results raised questions concerning the involvement of the passive tissues and the use of deeper muscles during trunk axial rotation, which should be further investigated.     

Trunk muscle activation and cocontraction while resisting applied moments in a twisted posture

Abstract

Previous studies of twisting have revealed substantial cocontraction of agonist and antagonist muscles within the torso when torsional moments are generated. The objective of the current study was to quantify the activations and cocontraction of eight trunk muscles as subjects maintained an axially rotated trunk posture and resisted external applied bending moments. Ten subjects twisted their torsos 25° to the right (clockwise) and resisted 20 and 40 Nm bending moments from 12 directions. The moment directions were in a transverse plane and labelled clockwise as viewed from above, ranging from 0° (mid-saggital, anterior) to 330°, in 30° increments. RMS EMG amplitude data were collected using surface electrodes and normalized to maximal voluntary contractions. Significant changes were observed in the muscle responses due to the interaction of the moment direction and moment magnitude for six of the eight muscles tested. Comparison of the present data with that collected previously in neutral postures indicated: (1) a large increase in the activation levels of the right erector spinae and the left external oblique muscles; and (2) a counter-clockwise shift in the moment direction at which the peak activation of these same muscles occurs. Analysis of the relative activation levels (RALs), constructed from the NEMG data to quantify the cocontraction, indicated that the changes in cocontraction were more robust in response to changes in the bending moment's direction as opposed to changes in bending moment's magnitude.     

A novel optimization model for predicting trunk muscle forces during asymmetric lifting tasks

Low back pain (LBP) is a social and economic problem throughout industry. Repetitive asymmetric postures frequently occur in manual materials handling tasks and such asymmetric lifting has been epidemiologically linked to LBP. Therefore, biomechanical lifting models must be developed to predict muscle forces during asymmetric lifting tasks. This paper proposes an optimization model that was revised to take into account the activities of trunk muscles during asymmetric lifting tasks. Also, three optimization models (minimize maximum muscle intensity: MIN_I_MAX, minimize sum of magnitudes of the muscle forces raised to power 3: MIN_F³, and minimize sum of the muscle intensities raised to power 3: MIN_I³) are compared under various asymmetric lifting conditions. The revised model not only reflects the twisting effect of muscle force vectors for eight primary trunk muscles when trunk rotation is involved, but also accurately predicts the forces of left erector spinae, left latissimus dorsi and left external oblique muscles when compared with EMG signals obtained from experiments. Furthermore, MIN_I_MAX exhibits the best prediction capability among the three optimization models.Relevance to industryA novel optimization model proposed herein considers the twisting effect of muscle force vectors for eight trunk muscles when trunk rotation is involved. An accurate biomechanical model which reflects the asymmetric lifting conditions would significantly facilitate the evaluation of job and workplace design as well as provide a practical clinical evaluation technique.     

An electromyographic investigation of asymmetric lifting and moving of a load: II. Effects of load lift from knuckle to target shelves

The range of normalized electromyography (EMG) values when lifting and moving a 5.84 kg box was between 0.08 and 0.63. The right iliocostalis and the left erector spinae showed decreased muscle activity with increasing asymmetry. The right erector spinae and the left and the right external obliques showed significant increases in muscle activity at 90° asymmetry. The left and the right iliocostalis, the left erector spinae, and the right external oblique showed significant reductions in muscle activity for the sternum height when compared to the knuckle height. The right erector spinae exhibited a significant increase at reach height when compared to the knuckle height. The muscle activity for the knuckle lift was significantly lower than the floor lift. The average decrease in muscle activity was approximately 68%. Consequently, asymmetric lifting and moving tasks should be performed from a knuckle height to sternum height. © 2009 Wiley Periodicals, Inc.     

Characterisation of trunk muscle activation amplitude patterns during a simulated checkstand operation with continuously changing flexor and lateral moment demands

While the typical physical exposure to modern-day workers has changed from heavy to low level repetitive demands, there is limited research that examines light occupations. This study examined trunk muscle recruitment strategies in response to a simulated checkout operation. Surface electromyography and kinematic variables were recorded from 29 healthy subjects. Four principal patterns accounted for 95.3% of the variation. Significant differences in scores captured different strategies in response to reach conditions and external moment directions. Synergistic co-activation of ipsilateral back sites and differential activation among external oblique and erector spinae sites suggests that the central nervous system may control different regions of the trunk musculature to optimally account for asymmetrical demands. The strategy between the internal oblique and back extensor sites suggests that a specific co-activation strategy may be needed during lighter work. During low-load occupational tasks, several recruitment strategies were required to maintain spinal stability and account for changing external moments.

Statement of Relevance: Different recruitment strategies found in response to changing external moments offer new insights into neuromuscular control for lighter work. Specifically, multiple trunk muscle sites interact in a complex manner, taking into account task specificity and individual variation that are valuable in workstation design, evaluating injury risk and estimating spinal loads.     

Are hybrid sit–stand postures a good compromise between sitting and standing?

Potential alternatives for conventional sitting and standing postures are hybrid sit-stand postures (i.e. perching). The purposes of this study were (i) to identify where lumbopelvic and pelvic angles deviate from sitting and standing and (ii) to use these breakpoints to define three distinct postural phases: sitting, perching, and standing, in order to examine differences in muscle activations and ground reaction forces between phases. Twenty-four participants completed 19 1-min static trials, from sitting (90°) to standing (180°), sequentially in 5°trunk–thigh angle increments. The perching phase was determined to be 145–175° for males and 160–175° for females. For both sexes, knee extensor activity was lower in standing compared to perching or sitting (p < .01). Anterior–posterior forces were the highest in perching (p < .001), requiring ～15% of body-weight. Chair designs aimed at reducing the lower limb demands within 115–170° trunk–thigh angle may improve the feasibility of sustaining the perched posture.

Practitioner summary: Individuals who develop low back pain in sitting or standing may benefit from hybrid sit-stand postures (perching), yet kinematic and kinetic changes associated with these postures have not been investigated. Perching can improve lumbar posture at a cost of increased lower limb demands, suggesting potential avenues for chair design improvement.

Abbreviations: A/P: anterior-posterior; M/L: medial-lateral; LBP: low back pain; EMG: electromyography; TES: thoracic erector spinae; LES: lumbar erector spinae; VMO: vastus medialis obliquus; MVC: maximum voluntary contraction; ASIS: anterior superior iliac spine; PSIS: posterior superior iliac spine; BW: body weight; RMSE: root mean square error; SD: standard deviation; ROM: range of motion     

Comparison of three strategies of trunk support during asymmetric two-handed reach in standing

No trunk support (NTS) was compared to a lower trunk support (LTS) of leaning against a worktable and a dynamic upper trunk support (UTS) using postural kinematics, trunk extensor muscle activity and subjective rating of both comfort and effort. Ten females completed 3 repetitions where they lifted 0 and 5 kg load from a symmetrical position at hip-height to a 45° asymmetric position at: i) hip-height and ii) shoulder-height. Human motion capture showed trunk flexion decreased by 12° ± 10 with trunk support with hip-height reach. The table blocked axial rotation of the pelvis which was compensated by an additional 8° ± 6 rotation of the thoracic segment. Surface EMG of the lumbar erector spinae, contralateral to reach, showed the UTS to be almost twice as effective as the LTS with shoulder-height reach with a 30% ± 18 reduction. With hip-height reach, UTS resulted in a smaller reduction equal to 23% ± 27 while the LTS had no effect. Further investigation is needed to determine optimal performance parameters for trunk support with complex, dynamic trunk postures and whether altered kinematics arising from LTS have higher risk of upper back discomfort.     

Study on the variation of peak isometric strength and EMG activity in static field-simulated lifting postures

Peak isometric strength was measured from 10 adult Indian construction workers in eight different field-simulated (FS) postures. This peak-strength data in these FS postures were compared with symmetric postures. In symmetric postures, the vertical load positions were kept the same as FS postures and the points of force exertion were fixed at 40 cm distance in front of the subject. From both symmetric and FS static strength data, it was shown that the maximum peak strength occurred at medium vertical height level and decreased with both increase and decrease of the vertical height level. The maximum and minimum peak strengths were obtained in different FS postures as 222.85±61.15 N and 85.65±19.89 N, respectively. It was observed that the lifted weight in the field was 12.0 kg, which corresponds to 54.54% and 137.3% (i.e. >100%) of these maximum and minimum peak-strength values. This result indicated the prevalence of high risk factors in the field. During this study, surface EMGs from four different muscles (i.e. trapezius, external oblique, rectus abdominis and erector spinae) were collected while exerting the peak isometric strength. From ANOVA analysis, it was shown that the erector spinae and trapezius activities were significantly (p⩽0.05) related to the peak-strength value, whereas external oblique and rectus abdominis activities were not. It was also observed that RMS of erector spinae activity increases with ipsi-lateral increase of asymmetry angle along with the decrease in maximum static peak-strength level in FS postures.Relevance to industryThe peak static strength and EMG activities were measured in FS postures to highlight the potential risk factors in building construction industry. This study was conducted on adult female building construction workers, where the female construction workers were not well represented in the literature. Moreover, from this study, it is very clear that the actual field postures are of more complex in nature than the simulation studies, as mentioned in earlier studies.     

An evaluation of backpack harness systems in non-neutral torso postures

Much of the research on backpack design has been focused on spinal loading/biomechanics while the wearer is in a neutral/upright trunk posture, such as those employed by outdoor enthusiasts and schoolchildren. This research has led to some important harness design improvements that reduce trunk muscle exertions, fatigue and improve overall comfort. There are number of occupations, however, wherein workers wear back-mounted packs/devices (e.g. air tanks) while working in non-neutral trunk postures. The objective of the current study was to evaluate the effects of these non-neutral postures on biomechanical loading and then reconsider the backpack system design recommendations. Fifteen participants were asked to support a 18.2 kg load on their back while assuming static forward flexed postures of the torso (15 degrees , 30 degrees , 45 degrees , and 60 degrees of sagittal bend). The mass on the back was attached to the participant through two different harness mechanisms: a basic harness design (as seen on college student backpacks) and a more advanced design containing lateral stiffness rods and a weight-bearing hip belt (as seen on backpacks for hikers). While performing these static, posture maintenance tasks, the activation levels of the bilateral trapezius, erector spinae, and rectus abdominis were collected. Participants also provided subjective ratings of comfort. The results showed that there was a significant interaction between harness type and forward flexion angle for the trapezius and the erector spinae muscles. The normalized EMG for the trapezius muscles showed a 14% and 11% reduction in muscle activity at 15 degrees and 30 degrees , respectively, with the advanced design but these positive effects of the advanced design were not found at the greater flexion angles. Likewise the erector spinae muscles showed a 24% and 14% reduction in muscle activity at 15 degrees and 30 degrees , respectively, with the advanced design harness but these effects of the advanced design were not found at the greater forward flexion angles. The level of forward flexion angle affected the rectus abdominis muscle activity, but neither the harness type main effect nor the interaction of harness type and forward flexion angle was significant. The subjective survey results agreed with the EMG results and showed the advanced design harness was generally more comfortable with respect to the shoulder and low back areas. Collectively, the subjective and objective results show a significant improvement with the advanced harness system but also note an interesting interaction with degree of sagittal flexion, indicating a diminished effectiveness of the design improvements at forward flexed postures. Design criteria for harness systems in these forward flexed postures are discussed.     

Postural and trunk muscle response to sudden release during stoop lifting tasks before and after fatigue of the trunk erector muscles

The effect of fatigue on the muscular and postural response to sudden release of different stoop lifting loads was studied. Ten male volunteers performed a series of stoop lifting trials before and after fatigue of the erector spinae. Trials were performed using loads of 20, 40, 60, and 80 N, and sudden release of load was triggered randomly on one of the repetitions using an electromagnetic release. The onset of release was registered by an accelerometer, centre of pressure (COP) motion was recorded via a forceplate, and EMG activities of the latissimus dorsi (LD), erector spinae (ES), rectus abdominus (RA), external oblique (EO) and internal oblique (IO) muscles were recorded. A slightly reduced lifting speed was seen after fatigue, particularly at the higher loads, but this had little effect on the perturbing force at release, which was dominated by the release load. A significant effect of fatigue was seen on the antero-posterior COP motion, with the postural disturbance being decreased after fatigue. Fatigue resulted in a significant increase in ES (p = 0.029) and LD (p = 0.015) relaxation times and, while the response patterns (relaxation, contraction or no response) of the anterior trunk muscles (RA, EO, IO) were not always consistent, the proportion of response by relaxation was greater after fatigue. This resulted in a lower incidence but longer duration of co-contraction of the ES-RA, ES-EO and ES-EO muscle groups following fatigue, such that the mean co-contraction duration of these groups showed no significant differences before and after fatigue. The response to sudden release is a balance between maintaining postural stability and at the same time preventing the trunk musculature from overloading the spine and risking tissue injury. While fatigue of the trunk extensors does not appear to increase either the risk of fall or stumble or the incidence of co-contraction following sudden release of stoop lifting tasks, the duration of co-contraction appears to increase following fatigue. Further study is required to quantify the loading on the spine during sudden release of different lifting tasks before and after more realistic fatigue conditions.     

Physiological responses to weight lifting in different planes

A weight of 10 kg was lifted by 11 normal male volunteers (mean age 34·2 years) from ground to knee, hip, and shoulder levels in the sagittal, lateral and oblique planes. During these lifting manoeuvres intra-abdominal pressure was measured by telemetry and the activity of erector spinae and external oblique were recorded by electromyography. The values obtained for peak and sustained intra-abdominal pressure and the averaged electromyographic activities of erectores spinae and external obliques were subjected to analysis of variance and correlation analysis. A significant difference between the responses in these three planes was found: the sagittal plane activities evoke least response. Intra-abdominal pressures, erector spinae activity and external oblique activity were highly significantly correlated in each of the three planes.     

Bowing with a trunk flexion of 90°: Perspectives on consumers and service personnel

In this study, we analyzed 100 questionnaire responses to determine consumer conceptions of service personnel bowing as a gesture of politeness. In addition, 12 female participants demonstrate five distinct degrees of bowing by bending their trunk 30°, 45°, 60°, and 90° from an upright position; their spinal curvature and trunk muscle activations were measured. The results showed that most respondents believed that bowing at 30° was the most satisfactory angle, followed by 45°. Bowing at 45° or 60° caused the survey respondents to feel honored, whereas bowing at 90° induced feelings of surprise and novelty; however, this angle produced the lowest proportion level of agreements on the items at ease, necessary, and appropriate among the 100 respondents. When the 12 participants bowed at an angle ≤60°, their spinal posture became increasingly kyphotic, and their muscle activations became more pronounced. Myoelectric silencing of the erector spinae was observed when the participants bowed at 90°, which can increase the risk of low back injury. These findings provide service industries with a reference for the design of service encounters.Relevance to industryBowing has traditionally signified politeness and respect in many countries. However, whether bowing at a greater trunk flexion actually satisfies customers remains unclear. Findings from this study clarify the customer perceptions and body loads of service personnel when bowing at various trunk positions. The extreme bowing postures (e.g., 90° trunk flexion) should be avoided.     

Effects of dynamic office chairs on trunk kinematics,trunk extensor EMG and spinal shrinkage

Seated work has been shown to constitute a risk factor for low-back pain. This is attributed to the prolonged and monotonous low-level mechanical load imposed by a seated posture. To evaluate the potential health effects with respect to the low back of office chairs with a movable seat and back rest, trunk kinematics, erector spinae EMG, spinal shrinkage and local discomfort were assessed in 10 subjects performing simulated office work. On three separate occasions subjects performed a 3 h task consisting of word processing, computer-aided design and reading. Three chairs were used, one with a fixed seat and back rest and two dynamic chairs, one with a seat and back rest movable in a fixed ratio with respect to each other, and one with a freely movable seat and back rest. Spinal shrinkage measurements showed a larger stature gain when working on the two dynamic chairs as compared with working on the chair with fixed seat and back rest. Trunk kinematics and erector spinae EMG were strongly affected by the task performed but not by the chair type. The results imply that dynamic office chairs offer a potential advantage over fixed chairs, but the effects of the task on the indicators of trunk load investigated were more pronounced than the effects of the chair.     

Effects of dynamic office chairs on trunk kinematics, trunk extensor EMG and spinal shrinkage.

Seated work has been shown to constitute a risk factor for low-back pain. This is attributed to the prolonged and monotonous low-level mechanical load imposed by a seated posture. To evaluate the potential health effects with respect to the low back of office chairs with a movable seat and back rest, trunk kinematics, erector spinae EMG, spinal shrinkage and local discomfort were assessed in 10 subjects performing simulated office work. On three separate occasions subjects performed a 3 h task consisting of word processing, computer-aided design and reading. Three chairs were used, one with a fixed seat and back rest and two dynamic chairs, one with a seat and back rest movable in a fixed ratio with respect to each other, and one with a freely movable seat and back rest. Spinal shrinkage measurements showed a larger stature gain when working on the two dynamic chairs as compared with working on the chair with fixed seat and back rest. Trunk kinematics and erector spinae EMG were strongly affected by the task performed but not by the chair type. The results imply that dynamic office chairs offer a potential advantage over fixed chairs, but the effects of the task on the indicators of trunk load investigated were more pronounced than the effects of the chair.     

Effect of wearing jeans on the back muscle flexion-relaxation phenomenon

The flexion–relaxation phenomenon (FRP) in back muscles is related to the lower back load. Although the FRP has been widely discussed, the effect of wearing jeans—a common attire in workplaces—on the FRP is unexplored. This study recruited 20 male participants with high and low flexibilities (10 each) and measured the related muscle activity and lumbopelvic movement at five trunk flexion angles (0°–90°) when wearing two types of bottom wears (swim trunks and fit jeans). Results revealed that the bottom wear type and trunk angle significantly affected all responses, whereas flexibility affected only erector spinae and hamstring activities. Participants with high flexibility and wearing swim trunks exhibited greater erector spinae activity than did those with low flexibility and wearing jeans. Thus, those who have low flexibility or are wearing jeans are likely to experience more activity reductions in erector spinae. However, the result with hamstring activity was the opposite. Wearing jeans limited participants’ pelvic rotation, forcing them to bend their lumbar spine further to complete trunk flexion, thus reducing erector spinae activity. A looser attire should be chosen to avoid constraining the pelvic rotation when work involves a deep trunk flexion.Relevance to industryPeople wearing jeans have limited pelvic movement and decreased erector spinae activity during deep trunk flexion, and this may further strain their interspinous ligaments. Thus, people should not wear fit jeans when in workplaces where their work involves stooping or trunk flexion exceeding 45° to minimize the load on their lower back.     

Using sitting as a component of job rotation strategies: Are lifting/lowering kinetics and kinematics altered following prolonged sitting

Workers are often required to perform manual materials handling tasks immediately following periods of prolonged sitting either as a secondary job component of as different tasks in a job rotation strategy. The goal of this investigation was to determine if changes to low-back kinetics and/or kinematics occurred during repetitive lifting/lowering exertions following extended seated exposures. Upper body kinematics, lumbar spine flexion angle, pelvic orientation and bilateral muscle activity from the external abdominal obliques and lumbar erector spinae were recorded for 8 males and 8 females while they alternated between sessions of repetitive lifting/lowering and prolonged sitting. Upper body kinematics were used as inputs to a linked segment model to compute low-back flexion/extension moments, compression, and shear. Peak lumbar flexion was reduced by 1.8° during the lifting/lowering exertions following the first hour of sitting which consequently led to a reduction of approximately 50 N in the reaction anteroposterior shear forces. Sitting postures were consistent with previously reported data. The reduced shear loads during repetitive lift/lower exertions following prolonged sitting may be a consequence of alterations in passive tissue properties which could alter the risk of low-back injury, although future research is required to examine the biomechanical significance of this finding. Changes to both kinematics and kinetics were minimal suggesting that using prolonged sitting as a component of a task series in job rotation does not alter the risk present when combined with repetitive lifting tasks.     

Postural and trunk muscle response to sudden release during stoop lifting tasks before and after fatigue of the trunk erector muscles

The effect of fatigue on the muscular and postural response to sudden release of different stoop lifting loads was studied. Ten male volunteers performed a series of stoop lifting trials before and after fatigue of the erector spinae. Trials were performed using loads of 20, 40, 60, and 80N, and sudden release of load was triggered randomly on one of the repetitions using an electromagnetic release. The onset of release was registered by an accelerometer, centre of pressure (COP) motion was recorded via a forceplate, and EMG activities of the latissimus dorsi (LD), erector spinae (ES), rectus abdominus (RA), external oblique (EO) and internal oblique (IO) muscles were recorded. A slightly reduced lifting speed was seen after fatigue, particularly at the higher loads, but this had little effect on the perturbing force at release, which was dominated by the release load. A significant effect of fatigue was seen on the antero-posterior COP motion, with the postural disturbance being decreased after fatigue. Fatigue resulted in a significant increase in ES (p = 0.029) and LD (p = 0.015) relaxation times and, while the response patterns (relaxation, contraction or no response) of the anterior trunk muscles (RA, EO, IO) were not always consistent, the proportion of response by relaxation was greater after fatigue. This resulted in a lower incidence but longer duration of co-contraction of the ES-RA, ES-EO and ES-EO muscle groups following fatigue, such that the mean co-contraction duration of these groups showed no significant differences before and after fatigue. The response to sudden release is a balance between maintaining postural stability and at the same time preventing the trunk musculature from overloading the spine and risking tissue injury. While fatigue of the trunk extensors does not appear to increase either the risk of fall or stumble or the incidence of co-contraction following sudden release of stoop lifting tasks, the duration of co-contraction appears to increase following fatigue. Further study is required to quantify the loading on the spine during sudden release of different lifting tasks before and after more realistic fatigue conditions.     

A biomechanical analysis of anterior load carriage

Front load carriage is a common occupational task in some industries (e.g. agriculture, construction), but, as compared to lifting tasks, relatively little research has been conducted on the biomechanical loading during these activities. The focus of this study was to explore the low back biomechanics during these activities and, specifically, to examine the effects of load height and walking speed on trunk muscle activity and trunk posture. Eleven male participants participated in two separate front load-carriage experiments. The first experiment called for carrying a barbell (with weight corresponding to 20% of elbow flexion strength) at three heights (knuckle height, elbow height and shoulder height) at a constant horizontal distance from the spine. The second experiment called for participants to carry a bucket of potatoes weighing 14 kg at the same three heights, but with no further restrictions in technique. In both experiments, the participants performed this task while either standing still or walking at a self-selected speed. As they performed these tasks, the activity levels of the right-side muscle of the rectus abdominis, external oblique, biceps brachii, anterior deltoid and three levels (T9, T12 and L3) of the erector spinae were sampled. Mid-sagittal plane trunk posture was also quantified using three magnetic field-based motion sensors at T9, T12 and L3. The results showed a significant effect of both walking speed and load height on trunk posture and trunk muscle activity levels in both the barbell and bucket experiments. In the barbell experiment, the walking trials generated 43% more trunk muscle activity than the standing trials. Trials at shoulder height produced 11% more muscle activity than trials at elbow height in the T9 erector spinae muscles and 71% more muscle activity in the anterior deltoid. In the bucket experiment, trunk muscle activity responded in a similar fashion, but the key result here was the quantification of the natural hyperextension posture of the spine used to balance the bucket of potatoes. These results provide insight into muscle activation patterns in dynamic settings, especially (load) carrying biomechanics, and have implications in industrial settings that require workers to carry loads in front of their bodies.     

Effects of restrictive clothing on lumbar range of motion and trunk muscle activity in young adult worker manual material handling

The objective of this study was to examine the effect of wearing restrictive trousers on lumbar spine movement, trunk muscle activity and low back discomfort (LBD) in simulations of manual material handling (MMH) tasks. Twenty-eight young adults participated in the study performing box lifting, liquid container handling while squatting, and forward reaching while sitting on a task chair when wearing tight pants (sizes too small for the wearer) vs. fit pants (correct size according to anthropometry). Each task was repeated three times and video recordings were used as a basis for measuring lumbar range of motion (LRoM). The response was normalized in terms on baseline hip mobility. Trunk muscle activity of rectus abdominis (RA) and erector spinae (ES) muscles were also measured in each trial and normalized. At the close of each trial, participants rated LBD using a visual analog scale. Results revealed significant effects of both pants and task types on the normalized LRoM, trunk muscle activity and subjective ratings of LBD. The LRoM was higher and trunk muscle (ES) activity was lower for participants when wearing tight pants, as compared to fit pants. Discomfort ratings were significantly higher for tight pants than fit. These results provide guidance for recommendations on work clothing fit in specific types of MMH activities in order to reduce the potential of low-back pain among younger workers in industrial companies.