Acceptable weights and physiological costs of performing combined manual handling tasks in restricted postures

Eight healthy, male underground coal miners (mean age = 36.9 yrs +/- 4.5 SD) participated in a study examining psychophysically acceptable weights and physiological costs of performing combined lifting and lowering tasks in restricted head-room conditions. Independent variables included posture (stooping or kneeling on two knees), task symmetry (symmetric or asymmetric), and vertical lift distance (35 cm or 60 cm). All tasks were 10 min in duration and were performed under a 1.22 m ceiling to restrict the subject's posture. Subjects were required to raise and lower a lifting box every 10s, and asked to adjust the box weight to the maximum amount they could handle without undue strain or fatigue. During the final 5 min of each test, data were collected to determine the energy expenditure requirements of the task. Results of this study demonstrated that psychophysical lifting capacity averaged 11.3% lower when kneeling as compared to stooping. Subjects selected 3.5% more weight in asymmetric tasks, and lifted 5.0% less weight to the 60 cm shelf compared to the 35 cm shelf. Heart rate was not significantly affected by posture, but was increased an average of 4 beats/min in asymmetric conditions, and by 3.5 beats/min while lifting/lowering to/from the high shelf. Oxygen uptake was increased by 9% when stooped, by 10% when lifting/lowering asymmetrically, and by 8.2% when performing the task to the high shelf. Results of this study indicate that, wherever possible, materials that must be lifted manually in low-seam coal mines be designed in accordance with the decreased lifting capacity exhibited in the kneeling posture.     

Acceptable weights and physiological costs of performing combined manual handling tasks in restricted postures

Eight healthy, male underground coal miners (mean age=36·9 yrs±4·5 SD) participated in a study examining psychophysical acceptable weights and physiological costs of performing combined lifting and lowering tasks in restricted headroom conditions. Independent variables included posture (stooping or kneeling on two knees), task symmetry (symmetric or asymmetric), and vertical lift distance (35 cm or 60cm). All tasks were 10min in duration and were performed under a 1·22 m ceiling to restrict the subject's posture. Subjects were required to raise and lower a lifting box every 10 s, and asked to adjust the box weight to the maximum amount they could handle without undue strain or fatigue. During the final 5 min of each test, data were collected to determine the energy expenditure requirements of the task. Results of this study demonstrated that psychophysical lifting capacity averaged 11·3% lower when kneeling as compared to stooping. Subjects selected 3·5% more weight in asymmetric tasks, and lifted 5·0% less weight to the 60 cm shelf compared to the 35 cm shelf. Heart rate was not significantly affected by posture, but was increased an average of 4 beats/min in asymmetric conditions, and by 3·5 beats/min while lifting/lowering to/from the high shelf. Oxygen uptake was increased by 9% when stooped, by 10% when lifting/lowering asymmetrically, and by 8·2% when performing the task to the high shelf. Results of this study indicate that, wherever possible, materials that must be lifted manually in low-seam coal mines be designed in accordance with the decreased lifting capacity exhibited in the kneeling posture.     

Spinal loading in static and dynamic postures: EMG and intra-abdominal pressure study

Abstract

The difference in physiological stress between static posture loading and dynamic lift is poorly understood. Therefore, the quantitative pattern of gradual increase and decrease of stress as measured by EMG of erectores spinae at T₁₂ and L₃ and intraabdominal pressure (IAP) due to steady progressive loading and unloading in static stooping posture was studied and compared with that of stoop lifting of the same weight. For dynamic loading and unloading a steady flow of 25 kg of water into or out of a plastic tub held in the hand while maintaining a stooping posture was used. The subjects also performed stoop lifting weights of 15 and 25 kg. In static posture loading the mean EMG at T₁₂ was approximately 50% of the L₃ level. During unloading in that posture it was reduced to 33%. The level of electromyographic activity at T₁₂ for loading was not significantly different from unloading. At L₃ however, the magnitude increased significantly for unloading. The EMG and intraabdominal pressure responses of static posture were between 33 and 50% of the corresponding phases during stoop lifting of the same weight. An insignificant difference in IAP and heart rate between static posture loading and stoop lifting indicates a less critical role of IAP and no difference in cardiac stress in less stressful tasks.     

Combined exposures of whole-body vibration and awkward posture: a cross sectional investigation among occupational drivers by means of simultaneous field measurements

Abstract

Objective: Multifactorial workloads such as whole-body vibration (WBV), awkward posture and heavy lifting are potential predictors for low back pain (LBP). In this study, we investigate the association between LBP and these exposures among 102 professional drivers. Methods: The combined exposures of WBV and posture are measured at different workplaces. Health and personal data as well as information about lifting tasks are collected by a questionnaire. Results: The daily vibration exposure value (odds ratio 1.69) and an index for awkward posture (odds ratio 1.63) show significant association with the occurence of LBP. Awkward posture and heavy lifting appear to be more strongly associated with sick leave than WBV exposure. Furthermore, a combination of the measurement results of WBV and awkward posture into one quantity also shows significant correlation to LBP. Conclusion: The combined exposure of WBV and awkward posture can be described in terms of the daily vibration exposure and the index for awkward posture. This facilitates work place assessments and future research in this area.

Practitioner Summary: For the first time, quantitative measures combining whole-body vibration and awkward posture exposures have shown to correlate with the occurrence of low back pain significantly. This validates the proposed quantities and measurement methods, which facilitate workplace assessments and assist in the design of further studies which are necessary to establish a causal exposure–response relationship.     

Preparation of dynamic posture and occurrence of low back pain.

Improper posture is considered as one of the causes for low back pain. This study focused attention on low back pain that occurs when people adopt a dynamic posture. Low back pain in attendants was investigated as a typical example of low back pain in a dynamic posture. When multi-dimensional quantification III was applied to the results of the investigation, low back pain was found to occur in six postural patterns: bending knee posture, the posture of lifting and holding a light object, the posture of tilting the trunk, working posture to push a cart, the posture of turning or lifting a cart, and the posture of stretching. This survey found that low back pain frequently occurred when an unexpected load was imposed on the lumbar region and experiments were conducted to simulate the unexpected loading of this region. The experimental results showed that lumbar muscular activity was not fast enough to cope with the load and resulted in an increased swaying of the trunk. This swaying was considered to induce a load on the lumbar region. It is concluded that low back pain can be prevented if an appropriate preparatory set is taken.     

Preparation of dynamic posture and occurrence of low back pain

Abstract

Improper posture is considered as one of the causes for low back pain. This study focused attention on low back pain that occurs when people adopt a dynamic posture. Low back pain in attendants was investigated as a typical example of low back pain in a dynamic posture. When multi-dimensional quantification III was applied to the results of the investigation, low back pain was found to occur in six postural patterns: bending knee posture, the posture of lifting and holding a light object, the posture of tilting the trunk, working posture to push a cart, the posture of turning or lifting a cart, and the posture of stretching. This survey found that low back pain frequently occurred when an unexpected load was imposed on the lumbar region and experiments were conducted to simulate the unexpected loading of this region. The experimental results showed that lumbar muscular activity was not fast enough to cope with the load and resulted in an increased swaying of the trunk. This swaying was considered to induce a load on the lumbar region. It is concluded that low back pain can be prevented if an appropriate preparatory set is taken.     

The effects of horizontal load speed and lifting frequency on lifting technique and biomechanics

Lifting loads that have a horizontal velocity (e.g. lifting from a conveyor) is often seen in industry and it was hypothesised that the inertial characteristics of these loads may influence lifting technique and low back stress. Seventeen male participants were asked to perform lifting tasks under conditions of four horizontal load speeds (0 m/s, 0.7 m/s, 1.3 m/s and 2.4 m/s) and two lifting frequencies (10 and 20 lifts/min) while trunk motions and trunk muscle activation levels were monitored. Results revealed that increasing horizontal load speed from 0 m/s to 2.4 m/s resulted in an increase in peak sagittal angle (73° vs. 81°) but lower levels of peak sagittal plane angular acceleration (480°/s² vs. 4°/s²) and peak transverse plane angular acceleration (200°/s per s vs. 140°/s per s) and a consistent increase in trunk muscle co-activation. Participants used the inertia of the load to reduce the peak dynamics of the lifting motion at a cost of increased trunk flexion and higher muscle activity.

Statement of Relevance: Conveyors are ubiquitous in industry and understanding the effects of horizontal load speed on the lifting motions performed by workers lifting items from these conveyors may provide some insight into low back injury risk posed by these tasks.     

Effects of age and its interaction with task parameters on lifting biomechanics

This study investigated the age-related differences in lifting biomechanics. Eleven younger and 12 older participants were instructed to perform symmetric lifting tasks defined by different combinations of destination heights and load magnitudes. Lifting biomechanics was assessed. It was found that the trunk flexion in the starting posture was 32% lower and the peak trunk extension velocity was 46% lower in older participants compared with those in younger ones, indicating that older adults tended to use safer lifting strategies than did younger adults. Based on these findings, we recommend that physical exercise programmes may be a more effective ergonomic intervention for reducing the risks of low back pain (LBP) in lifting among older workers, compared with instructions of safe lifting strategies. As for younger workers, instructions of safe lifting strategies would be effective in LBP risk reduction.     

The load on the back in different handling operations

The study consisted of two parts. In part one the load on the back and muscle fatigue in bimanual symmetrical lifting from floor to table were studied in a lifting experiment of 1 hour' s duration. The following weights and lifting frequencies were used. 10% of max. lifting capacity (MLC) 6 and 15 times per min, 25% MLC 5 and 10 times per min and 50% MLC 3 and 6 times per min. The EMG mean amplitude from the back muscles (L3) showed that even light burdens (10 kg) cause considerable back-toads equivalent to 40–50% MVC. When lifting 50 kg burdens short lasting backloads near the MVC were present. Mean amplitudes and mean spectral frequencies of the EMG were in general increasing, respectively decreasing, as the lifting experiment progressed. Such changes in the EMG are normally interpreted as muscle fatigue caused by changes in the concentration of the chemical substances from the muscle. The EMG changes are most pronounced when lifting 50% MLC (6 times per min) and 10% MLC (15 times per min) and are to a higher extent dependent on the lifting frequency than on the weight or on the mechanical work performed on the burden. Further the RPE values from the back show the same pattern as the EMG. The V˙O₂ and HR, however, do not seem to discriminate as clearly between the different lifting tasks. In part two of the study the load on the back is studied by EMG during a number of manual handling operations applied when handling logs in the forest, i.e. frontal carrying, frontal carrying with a hook, frontal carrying with a pair of tongs, shoulder carrying and dragging with a pair of tongs. Three types of logs were used 1 m (30 kg), 3 m (30 kg), and 3 m (50 kg). All experiments were performed in the forest on two 5×3 m horizontal tracks standardized for the experiment, an easy and a difficult one. It was found that: normal manual handling operations in forestry work cause average backloads in young trained workers varying from 25% to 50% MVC, i.e. equivalent to 1400–2800 N extensor muscle tension of the back, assuming a 5 cm muscle lever arm. Backload levels equivalent to 75–100% MVC are present from a few per cent to 25% of the handling time in all the tasks studied. Asymmetrical loading of the back muscles is frequently seen most markedly in the lifting phases of the handling operations. Conclusion: the dragging method exposes the back to the smallest load on level smooth surface. Under difficult surface conditions, however, frontal carrying with hook and shoulder carrying seem to cause the smallest strain on the back. The backload measures obtained when lifting logs are considerably larger than the measures when lifting boxes of the same weight. Therefore, backload measures obtained in laboratory studies must be used with care when applied in actual working environments     

An electromyographic analysis of seated and standing lifting tasks.

The objective of this project was to compare the muscular effort exerted during manual lifting tasks performed in standing versus seated posture. Six male undergraduate and graduate students performed 12 different static and dynamic lifts in both sitting and standing positions. During each effort electromyographic (EMG) data were collected on four muscles groups (low back, upper back, shoulder, and abdominals). Four contractions were designed to elicit maximum muscular effort in the four groups being monitored. The remaining data were then expressed as a percentage of maximum EMG. Each subject performed the following: maximum static lift when sitting; maximum static lift when standing; sitting, static lift with 15.9 kg; standing, static lift with 15.9 kg; dynamic sit-forward lift with 15.9 kg, dynamic stand-forward lift with 15.9 kg, dynamic sit-twist with 15.9 kg, dynamic stand-vertical lift with 15.9 kg. Each of the lifts was performed with a wooden tray with slotted handles. Root mean square (RMS) values of the EMG data were calculated for three second periods. EMG activity in the low back, upper back, and shoulder was greater during sitting lifting than during standing lifting. The sit-twist lift resulted in the highest EMG in the abdominal muscles. Dynamic lifts resulted in more muscle activity than did static lifts. From these data it was concluded that sitting-lifting results in greater stress in the low back, upper back, and shoulders than does lifting while standing.     

Effect of a splint on measures of sustained grip exertion under different forearm and wrist postures

Despite the facts that gripping tasks have been found to be highly correlated with CTS and that splints are gaining popularity as personal protective equipment, the influence of splints on grip performance has not been determined adequately. The present study intends to investigate the influence of splints without the volar parts as well as of forearm and wrist postures on grip performances including maximal volitional contraction (MVC), maximum acceptable sustained time (MAST), cumulated exertion output (CEO), and normalized exertion level (NEL). Twenty college-student volunteers, 10 males and 10 females, were recruited. The factors of interest were gender, forearm position, wrist deviation, and splint (with and without). The forearm positions were set at 30 degrees internal shoulder rotation, 0 degrees internal shoulder rotation, and 30 degrees external shoulder rotation, the angles being measured between the sagittal plane and the long axis of dominant forearm. The wrist deviations were extension 30 degrees , neutral, and flexion 30 degrees , the angles being measured between the sagittal plane and the long axis of the grip gauge. The results indicate that the gender effect is the most dominantly significant on all evaluated response variables. Males have more MVC (220 vs. 337N), longer MAST (20.2 vs. 10.5s), and greater CEO (4306 vs. 1638Ns), but less NEL (66.6 vs. 73.9%MVC). The forearm posture is shown to be significant only on MVC. In addition, the effect of wrist posture cannot shift all responses, nor can the effect of splints. In general, a splint without volar part seems to be recommended while performing infrequent and forceful gripping tasks under the consideration of prevention, but there should be more information about the application of a splint without volar part while performing a repetitively gripping task.     

An electromyographic analysis of seated and standing lifting tasks

The objective of this project was to compare the muscular effort exerted during manual lifting tasks performed in standing versus seated posture. Six male undergraduate and graduate students performed 12 different static and dynamic lifts in both sitting and standing positions. During each effort electromyographic (EMG) data were collected on four muscles groups (low back, upper back, shoulder, and abdominals). Four contractions were designed to elicit maximum muscular effort in the four groups being monitored. The remaining data were then expressed as a percentage of maximum EMG. Each subject performed the following: maximum static lift when sitting; maximum static lift when standing; sitting, static lift with 15·9 kg; standing, static lift with 15·9 kg; dynamic sit-forward lift with 15·9 kg, dynamic stand-forward lift with 15·9 kg, dynamic sit-twist with 15·9 kg, dynamic stand-vertical lift with 15·9 kg. Each of the lifts was performed with a wooden tray with slotted handles. Root mean square (RMS) values of the EMG data were calculated for three second periods. EMG activity in the low back, upper back, and shoulder was greater during sitting lifting than during standing lifting. The sit-twist lift resulted in the highest EMG in the abdominal muscles. Dynamic lifts resulted in more muscle activity than did static lifts. From these data it was concluded that sitting-lifting results in greater stress in the low back, upper back, and shoulders than does lifting while standing.     

Lifting in four restricted lifting conditions: psychophysical, physiological and biomechanical effects of lifting in stooped and kneeling postures

Many underground coal mines are less than 1.2 m in height, and require that manual lifting tasks be performed in restricted postures (usually stooped or kneeling). Unfortunately, little is known about how these postures affect the underground coal miner's capabilities to perform such work. A previous Bureau of Mines study indicated that lifting capacity is greater when stooped than kneeling when lifting under a 1.2 m roof height (Gallagher et al, 1988). However, many low-seam coal mines present even more restricted headroom than 1.2 m. Therefore, a study was conducted to: (1) examine the psychophysical lifting capacity of low-seam coal miners under four restricted lifting conditions, (2) investigate the associated metabolic costs, and (3) analyse the electromyography (EMG) of trunk muscles when lifting in these restricted positions. Subjects were 12 coal miners accustomed to handling materials in restricted postures (mean age = 35.9 yrs +/- 6.4 SD). Results of this study indicated that lifting capacity was greater when the subjects could assume a stooped posture than when kneeling (p < 0.01). Furthermore, the metabolic cost was greater in the kneeling posture for heart rate (p < 0.001), oxygen consumption (p < 0.001), minute ventilation (p < 0.05] ), and respiratory exchange ratio (p < 0.05), despite the fact that miners lifted less weight in this posture. Analysis of the EMG data indicated increased activity of the electores spinae when kneeling (p < 0.001), but higher latissimus dorsi activity when stopped (p < 0.001). The findings of this study indicate that the weight of supply items should be reduced approximately 14-18% when the kneeling posture must be used for lifting.     

A comparison of different postures for scaffold end-frame disassembly

Overexertion and fall injuries comprise the largest category of nonfatal injuries among scaffold workers. This study was conducted to identify the most favourable scaffold end-frame disassembly techniques and evaluate the associated slip potential by measuring whole-body isometric strength capability and required coefficient of friction (RCOF) to reduce the incidence of injury. Forty-six male construction workers were used to study seven typical postures associated with scaffold end-frame disassembly. An analysis of variance (ANOVA) showed that the isometric forces (334.4-676.3 N) resulting from the seven postures were significantly different (p < 0.05). Three of the disassembly postures resulted in considerable biomechanical stress to workers. The symmetric front-lift method with hand locations at knuckle height would be the most favourable posture; at least 93% of the male construction worker population could handle the end frame with minimum overexertion risk. The static RCOF value resulting from this posture during the disassembly phase was less than 0.2, thus the likelihood of a slip should be low.     

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.     

An evaluation of the effect of a training program on worker lifting postures

Though worker training is often chosen as a means to reduce the risk of low back pain if involved in lifting activities, the effect on a worker's lifting posture is rarely reported. This paper describes a video analysis method of recording lifting postures and the results of one evaluation of a training program specifically designed to modify lifting postures. It is concluded that a four-hour training program had beneficial but minor effects on the lifting techniques used by healthy workers in a warehouse when handling relatively light to moderate loads (i.e., 85% of loads lifted were below 30 pounds).     

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.     

Changes in lifting dynamics after localized arm fatigue

The purposes of this study were (1) to compare the lifting strategies during arm fatigue and non-fatigue conditions and (2) to evaluate the effects of localized arm fatigue on L5/S1 compressive forces during lifting. The hypothesis was that isometrically induced arm fatigue can alter the lifting strategy selection resulting in an increase in the initial acceleration and leading to an increase in lower back stress. Biomechanical analyses of lifting were done before and after the performance of holding activity to induce arm muscle fatigue. Differences in the lifting strategies used including the accelerated effect, pre-lifting technique, and stiffening of the arms were monitored to determine their influence on L5/S1 compressive forces under various load and range conditions. The results show that lifting strategy changed significantly after arm fatigue, especially when the load was less than 20 kg. These changes included the use of increasingly stooped and accelerated techniques adopted at the beginning of the lift and stiffening of the arms at the end of the lift. Arm fatigue resulted in increased compressive forces at the L5/S1 disc due to the use of accelerated techniques and the inherent disadvantage of these techniques in the pre-lifting posture. In this study, lifting strategies changed as a function of arm fatigue, resulting in increased lower back loading. These findings suggest that whole-body lifting should be avoided after localized arm fatigue in order to decrease the risk of injury to the lower back.

Relevance to industry

Some industrial activities rely on the lifting of objects after arm holding or carrying tasks. Such tasks may lead to localized arm fatigue and become a dominant factor in workers choice of a lifting strategy. This study investigated the strategies adopted in response to changes in arm fatigue and their effects on the L5/S1 compressive forces during lifting. The results may have implications for lifting job design and provide useful information for further study in the prevention of low-back injuries.     

Dependence of safety margins in grip force on isometric push force levels in lateral pinch

This study examined the relationship between safety margin and force level during an isometric push task in a lateral pinch posture. Ten participants grasped an object with an aluminium- or rubber-finished grip surface using a lateral pinch posture and exerted 20%, 40%, 60%, 80% and 100% of maximum push force while voluntary grip force was recorded. Then minimum required grip force was measured for each push force level. Mean safety margin, the difference between voluntary and minimum required grip forces, was 25% maximum voluntary contraction (MVC) when averaged for all push levels. Safety margin significantly increased with increasing push force for both grip surfaces. Grip force used during maximum push exertion was only 74% lateral pinch grip MVC. Possible underlying mechanisms for increasing safety margin with increasing push force are discussed as well as the implication of this finding for ergonomic analysis. This study demonstrates that ergonomic analyses of push tasks that involve friction force should account for safety margin and reduced grip strength during the push. Failure to consider these can result in overestimation of people's push capability.     

The effect of fatigue on trunk muscle activation patterns and spine postures during simulated firefighting tasks

The purpose of this study was to determine the effect of a fatiguing task (3 min intense stair climbing) on the adopted spinal postures and trunk muscular activation patterns during three highly physically demanding simulated firefighting tasks. Following the fatigue protocol, it was observed that individuals adopted significantly greater spinal flexion (16.3° maximum prior to fatigue as compared to 20.1° post fatigue) and displayed reduced abdominal muscle activation as compared to before the fatigue protocol (mean ranging from 16.6% maximum voluntary contraction (MVC) to 30.6% MVC prior to fatigue as compared to ranging from 14.6% MVC to 25.2% MVC post fatigue). The reduced abdominal activation may be due to a reduction in co-contraction during these tasks, which may compromise spinal stability. Reduced co-contraction combined with the increased spinal flexion may increase the risk of sustaining an injury to the low back.