@article{shu_jiang_xu_mirka_2007, title={The effect of a knee support on the biomechanical response of the low back}, volume={23}, ISSN={["1065-8483"]}, DOI={10.1123/jab.23.4.275}, abstractNote={Stooping and squatting postures are seen in a number of industries (e.g., agriculture, construction) where workers must work near ground level for extended periods of time. The focus of the current research was to evaluate a knee support device designed to reduce the biomechanical loading of these postures. Ten participants performed a series of sudden loading tasks while in a semisquat posture under two conditions of knee support (no support and fully supported) and two conditions of torso flexion (45 and 60°). A weight was released into the hands of the participants who then came to steady state while maintaining the designated posture. As they performed this task, the EMG responses of the trunk extensors (multifidus and erector spinae) were collected, both during the “sudden loading” phase of the trial as well as the steady weight-holding phase of the trial. As expected, the effects of torso flexion angle showed significant decreases in the activation of the multifidus muscles with greater torso angle (indicating the initiation of the flexion–relaxation response). Interestingly, the results showed that the knee support device had no effect on the activation levels of the sampled muscles, indicating that the loss of the degree of freedom from the ankle joint during the knee support condition had no impact on trunk extensor muscle response. The a priori concern with regard to these supports was that they would tend to focus loading on the low back and therefore would not serve as a potential ergonomic solution for these stooping/semisquatting tasks. Because the results of this study did not support this concern, further development of such an intervention is underway.}, number={4}, journal={JOURNAL OF APPLIED BIOMECHANICS}, author={Shu, Yu and Jiang, Zongliang and Xu, Xu and Mirka, Gary A.}, year={2007}, month={Nov}, pages={275–281} }
 @article{shu_mirka_2006, title={A laboratory study of the effects of wrist splint orthoses on forearm muscle activity and upper extremity posture}, volume={48}, ISSN={["0018-7208"]}, DOI={10.1518/001872006778606859}, abstractNote={ Objective: To evaluate the effects of wrist splint orthoses (WSOs) on forearm muscle activity and upper extremity/torso postures. Background: WSOs are ubiquitous in industry, but the literature as to their biomechanical effects is limited. Method: Study 1: Participants performed single-plane wrist exertions with or without a WSO while the electromyographic (EMG) activity of the flexor carpi radialis, flexor carpi ulnaris, and extensor carpi ulnaris was captured. Study 2: Participants performed simple computer jumper installation tasks with or without a WSO while upper extremity/torso postures were recorded. Results: Study 1: A significant interaction between WSOs and wrist angle was observed in the response of forearm muscles (e.g., normalized EMG of the flexor carpi radial is increased from 4.2% to 15.9% as flexion increased from 0° to 36° in the orthosis conditions, whereas in the no-orthosis condition it remained 5% at all wrist flexion angles). Study 2: WSOs were found to effect wrist, torso, and shoulder postures, with the orthoses creating a 48% decrease (36° vs. 18.6°) in wrist flexion and 80% decrease (15° vs. -3°) in ulnar deviation but at a cost of increased shoulder abduction of 22% (36.5° vs. 44.5°) and increased lateral bend of torso of 30% (6° vs. 7.8°). Conclusions: WSOs increased forearm muscle activity at large wrist deviation angles and induced awkward shoulder postures in tasks requiring significant wrist deviation. Application: Use of WSOs in occupational settings should be carefully considered relative to task requirements, as orthoses may do more harm than good. }, number={3}, journal={HUMAN FACTORS}, author={Shu, Yu and Mirka, Gary A.}, year={2006}, pages={499–510} }
 @article{jiang_shu_drum_reid_mirka_2006, title={Effects of age on muscle activity and upper body kinematics during a repetitive forearm supination task}, volume={36}, ISSN={["1872-8219"]}, DOI={10.1016/j.ergon.2006.07.008}, abstractNote={The principal objective of this study was to assess the effects of age on upper extremity muscle activation patterns and upper body kinematics during a forearm supination task. Age-related physiological and biomechanical changes in the musculoskeletal system have been documented in the literature. It was hypothesized that these changes may have an impact on muscle recruitment and work technique (postural/kinematic) employed during work tasks. A simple repetitive forearm supination task was used to evaluate these hypotheses. Twenty subjects (ten in each age group 19–29 and 55–65) performed a series of static and dynamic forearm supination tasks on a work simulator. These exertions were performed at eight different levels of supination torque: 5–40 lb-in in 5 lb-in increments. As the subjects performed the static exertions the activation levels of several key muscles of the upper extremity were captured using surface electromyography. As the subjects performed the dynamic exertions, the motions of the upper body and upper extremity were captured using a magnetic field-based motion analysis system. The results of the static exertions showed that older subjects generated 135% greater trapezius muscle activity (significant at p<0.05 level) but no other muscle group sampled showed a significant difference between the age groups. In the dynamic exertions, age had no effect on upper limb/torso kinematic responses. In both the static and dynamic exertions, supination torque level had a significant impact on muscle activity and kinematics. These results provide empirical evidence that age alone does not have a consistent impact on biomechanical responses during physically demanding work tasks.}, number={11}, journal={INTERNATIONAL JOURNAL OF INDUSTRIAL ERGONOMICS}, author={Jiang, Zongliang and Shu, Yu and Drum, Jonathan and Reid, Stephanie and Mirka, Gary A.}, year={2006}, month={Nov}, pages={951–957} }
 @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} }