@article{shin_nance_mirka_2006, title={Differences in trunk kinematics and ground reaction forces between older and younger adults during lifting}, volume={36}, ISSN={["0169-8141"]}, DOI={10.1016/j.ergon.2006.05.008}, abstractNote={Age-related changes in trunk kinematics in lifting have received little attention despite a documented increased risk of musculoskeletal injury with age. This study examined the responses in trunk kinematics and ground reaction forces of older and younger subjects during lifting. Ten older (55–63 years) and ten younger (19–29 years) adults performed lifting tasks in six different conditions. A lumbar motion monitor was used to measure the subjects’ trunk kinematics and a force platform was used to measure the ground reaction forces during the lifting motion. The results of this study showed that age had a significant (p<0.05) effect on the transverse plane (axial twisting) trunk kinematics variables (peak velocity and peak acceleration) but did not affect ground reaction forces or other trunk kinematics variables. The peak transverse velocity was 40% lower and peak transverse acceleration was 30% lower in the older subjects as compared to the younger subjects. This study presents the postural adaptation of older subjects to dynamic lifting tasks. Results can be used to understand the risks of older work population in manual material handling tasks.}, number={9}, journal={INTERNATIONAL JOURNAL OF INDUSTRIAL ERGONOMICS}, author={Shin, Gwanseob and Nance, Mack L. and Mirka, Gary A.}, year={2006}, month={Sep}, pages={767–772} }
 @article{jiang_shin_freeman_reid_mirka_2005, title={A study of lifting tasks performed on laterally slanted ground surfaces}, volume={48}, ISSN={["0014-0139"]}, DOI={10.1080/00140130500123761}, abstractNote={Lifting in most industrial environments is performed on a smooth, level ground surface. There are, however, many outdoor work environments (e.g. agriculture and construction) that require manual material handling activities on variable grade ground surfaces. Quantifying the biomechanical response while lifting under these conditions may provide insight into the aetiology of lifting-related injury. The aim of the current study was to quantify the effect of laterally slanted ground surfaces on the biomechanical response. Ten subjects performed both isometric weight-holding tasks and dynamic lifting exertions (both using a 40% of max load) while standing on a platform that was laterally tilted at 0, 10, 20 and 30° from horizontal. As the subject performed the isometric exertions, the electromyographic (EMG) activity of trunk extensors and knee extensors were collected and during the dynamic lifting tasks the whole body kinematics were collected. The whole body kinematics data were used in a dynamic biomechanical model to calculate the time-dependent moment about L5/S1 and the time-dependent lateral forces acting on the body segments. The results of the isometric weight-holding task show a significant (p < 0.05) effect of slant angle on the normalized integrated EMG values in both the left (increase by 26%) and right (increase by 70%) trunk extensors, indicating a significant increase in the protective co-contraction response. The results of the dynamic lifting tasks revealed a consistent reduction in the peak dynamic L5/S1 moment (decreased by 9%) and an increase in the instability producing lateral forces (increased by 111%) with increasing slant angle. These results provide quantitative insight into the response of the human lifter under these adverse lifting conditions.}, number={7}, journal={ERGONOMICS}, author={Jiang, ZL and Shin, G and Freeman, J and Reid, S and Mirka, GA}, year={2005}, month={Jun}, pages={782–795} }
 @article{shu_drum_southard_shin_mirka_2005, title={The effect of a repetitive, fatiguing lifting task on horizontal ground reaction forces}, volume={21}, ISSN={["1065-8483"]}, DOI={10.1123/jab.21.3.260}, abstractNote={There are many outdoor work environments that involve the combination of repetitive, fatiguing lifting tasks and less-than-optimal footing (muddy/slippery ground surfaces). The focus of the current research was to evaluate the effects of lifting-induced fatigue of the low back extensors on lifting kinematics and ground reaction forces. Ten participants performed a repetitive lifting task over a period of 8 minutes. As they performed this task, the ground reaction forces and whole body kinematics were captured using a force platform and magnetic motion tracking system, respectively. Fatigue was verified in this experiment by documenting a decrease in the median frequency of the bilateral erector spinae muscles (pretest-posttest). Results indicate significant (p < 0.05) increases in the magnitude of the peak anterior/posterior (increased by an average of 18.3%) and peak lateral shear forces (increased by an average of 24.3%) with increasing time into the lifting bout. These results have implications for work environments such as agriculture and construction, where poor footing conditions and requirements for considerable manual materials handling may interact to create an occupational scenario with an exceptionally high risk of a slip and fall.}, number={3}, journal={JOURNAL OF APPLIED BIOMECHANICS}, author={Shu, Y and Drum, J and Southard, S and Shin, G and Mirka, GA}, year={2005}, month={Aug}, pages={260–270} }
 @article{mirka_shin_kucera_loomis_2005, title={Use of the CABS methodology to assess biomechanical stress in commercial crab fishermen}, volume={36}, ISSN={["1872-9126"]}, DOI={10.1016/j.apergo.2004.08.001}, abstractNote={Commercial fishing is a job characterized by long hours in an unpredictable, dynamic natural environment and variable demands placed on the musculoskeletal system, requiring strength, coordination, and endurance. The focus of this project was in the quantification of the biomechanical stresses placed on the lumbar spine during the work activities of commercial crab fishermen. The continuous assessment of back stress (CABS) methodology was used to develop distributions describing the amount of time that each of the crew members on a two- or three-man crabbing crew spend at various levels of low back stress. The results of this analysis, expressed in terms of time-weighted histograms, show significant inter and intra-crewmember variability in the stress measures during regular daily work activities. For the three man crew, the captain has relatively low stress levels throughout the work day, while the mate performs high force (up to 30 kg), dynamic exertions while pulling the crab pots from the water up into the boat and high loads (20-40 kg) during the loading and unloading of the boat in the morning and evening, respectively. The third man of the crew experiences static awkward postures (forward flexed postures held for up to 5 min at a time) as he sorts and packs the crabs. For the two-man crew, the results show a more even distribution of the high stress activities between the crewmembers. The application of the results of this analysis for prioritization of work tasks for ergonomic intervention is discussed.}, number={1}, journal={APPLIED ERGONOMICS}, author={Mirka, GA and Shin, G and Kucera, K and Loomis, D}, year={2005}, month={Jan}, pages={61–70} }
 @article{shin_shu_li_jiang_mirka_2004, title={Influence of knee angle and individual flexibility on the flexion-relaxation response of the low back musculature}, volume={14}, ISSN={["1050-6411"]}, DOI={10.1016/j.jelekin.2003.12.001}, abstractNote={In many occupational settings (e.g. agriculture and construction) workers are asked to maintain static flexed postures of the low back for extended periods of time. Recent research indicates that the resulting strain in the viscoelastic, ligamentous tissues may have a deleterious effect on the stability of the spine and the normal reflex response of spinal tissues. The purpose of this study was to evaluate the previously described flexion–relaxation response in terms of the interactive effect of trunk flexion angle (30°, 50°, 70°, 90°), knee flexion angle (0° (straight knees), 20°, 40°) and individual flexibiliteky (low, medium, and high). These conditions were tested under two levels of loading: no load (just supporting the weight of the torso) and trunk extension moment equal to 50% of the subject’s posture-specific maximum voluntary trunk extension capacity. Surface electromyographic (EMG) data were collected from the multifidus, the longissimus, the iliocostalis, the vastus medialis, the rectus femoris, the vastus lateralis, the biceps femoris, and the gastrocnemius-soleus group from a sample of eight male participants as they performed isometric weight holding tasks in the postures defined by the combinations of trunk angle and knee angle. The results of this study showed that knee angle did have a significant effect on the lumbar extensor muscle activity but only consistently at the 90° trunk angle. Participant flexibility showed a consistent trend of decreasing lumbar extensor muscle activity with decreased flexibility across all trunk angle values. Most interesting was the interactive response of flexibility and knee angle, wherein the flexibility of the participant influenced the trunk angles at which the knee flexion angle affected the flexion–relaxation response. Highly flexible subjects showed an effect of knee angle on the flexion–relaxation response only at the 90° trunk angle; subjects in the medium flexibility category showed a similar response in both the 70° and 90° trunk angles; subject in the low flexibility group showed no knee angle effect on the flexion–relaxation response. Overall the results confirm previous results with regard to the contribution of the passive tissues to the overall trunk extension moment but also show that the tension in the bi-articular biceps femoris, which was influenced by knee flexion angle and flexibility, affects the ratio of active extensor moment contributions of the lumbar extensor musculature to passive extensor moment contributions from the muscular and ligamentous tissues. The results of this study provide empirical data describing this complicated, interactive response.}, number={4}, journal={JOURNAL OF ELECTROMYOGRAPHY AND KINESIOLOGY}, author={Shin, G and Shu, Y and Li, Z and Jiang, ZL and Mirka, G}, year={2004}, month={Aug}, pages={485–494} }
 @article{shin_mirka_2004, title={The effects of a sloped ground surface on trunk kinematics and L5/S1 moment during lifting}, volume={47}, ISSN={["1366-5847"]}, DOI={10.1080/00140130310001653066}, abstractNote={There are many work environments that require workers to perform manual materials handling tasks on ground surfaces that are not perfectly flat (e.g. in agriculture, construction, and maritime workplaces). These sloped ground surfaces may have an impact on the lifting strategy/technique employed by the lifter, which may, in turn, alter the biomechanical loading of the spine. Describing the changes in kinematics and kinetics of the torso is the first step in assessing the impact of these changes and is the focus of the current research. Subjects' whole-body motions were recorded as they lifted a 10 kg box while standing on two inclined surfaces (facing an upward slope: 10° and 20°), two declined surfaces (facing a downward slope: − 10° and − 20°), and a flat surface (0°) using three lifting techniques (leg lift, back lift and freestyle lift). These data were then used in a two-dimensional, five-segment dynamic biomechanical model (top-down) to evaluate the effect of these slopes on the net moment about the L5/S1 joint. The results of this study showed an interesting interaction effect wherein the net L5/S1 moment was relatively insensitive to changes in slope angle under the back lift condition, but showed a significant effect during the leg lift and freestyle lifting conditions. The results show that under the freestyle lifting condition the peak L5/S1 moment was significantly higher for the inclined surfaces as compared to the flat surfaces (6.8% greater) or declined surfaces (10.0% greater). Subsequent component analysis revealed that both trunk flexion angle and angular trunk acceleration were driving this response. Collectively, the results of this study indicate that ground slope angle does influence the lifting kinematics and kinetics and therefore needs to be considered when evaluating risk of low back injury in these working conditions.}, number={6}, journal={ERGONOMICS}, author={Shin, G and Mirka, G}, year={2004}, month={May}, pages={646–659} }