@article{southard_mirka_2007, title={An evaluation of backpack harness systems in non-neutral torso postures}, volume={38}, ISSN={["1872-9126"]}, DOI={10.1016/j.apergo.2006.08.007}, abstractNote={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°, 30°, 45°, and 60° 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° and 30°, 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° and 30°, 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.}, number={5}, journal={APPLIED ERGONOMICS}, author={Southard, Stephanie A. and Mirka, Gary A.}, year={2007}, month={Sep}, pages={541–547} }
 @article{southard_freeman_drum_mirka_2007, title={Ergonomic interventions for the reduction of back and shoulder biomechanical loading when weighing calves}, volume={37}, ISSN={["0169-8141"]}, DOI={10.1016/j.ergon.2006.10.016}, abstractNote={Workers in the agriculture industry have exposure to many of the recognized risk factors for work-related musculoskeletal disorders. The focus of the current project was to develop and evaluate devices designed to reduce exposure to risk factors during the process of weighing beef calves. Ergonomic task analysis of current techniques used to weigh these calves indicated significant stress in the cervicobrachial and lumbar regions. Two ergonomic interventions—the “Handle Attachment” and the “Lever Arm”—were developed to improve the body posture of the lifter and reduce joint loading. A laboratory study and field evaluations were conducted for each of these designs. In the laboratory, muscle activities were quantified for the major muscles of cervicobrachial region, the lumbar region and knee extensor muscle group during the performance of the lifting task while using the two new interventions and the standard method. In the field evaluations, farmworkers used these devices and biomechanical models of the whole body postures were developed to quantify changes in the joint loading when using the interventions. The results show that both intervention techniques reduce the required muscle activity (8–71.6% reduction for the muscles of the cervicobrachial region, 2–43% reduction for the muscles of the lumbar region) and the joint loading (33–100% reduction in shoulder abduction moment and 42–57% reduction in spine compression) as compared to the standard method. Overall, the farmworkers noted that the “Handle Attachment” design is less cumbersome to move and use than the “Lever Arm” design, but laboratory study and field study revealed that the “Lever Arm” design provides the highest reduction in muscle activity and joint loading. Using either intervention while performing this task should decrease the risk to the low back and shoulders. The ergonomic intervention research described in this report documents a reduction in exposure to risk factors for shoulder and low back injury in an at-risk population in the agriculture industry.}, number={2}, journal={INTERNATIONAL JOURNAL OF INDUSTRIAL ERGONOMICS}, author={Southard, Stephanie A. and Freeman, Jacklyn H. and Drum, Jonathan E. and Mirka, Gary A.}, year={2007}, month={Feb}, pages={103–110} }
 @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} }