No abstract

Objective This study evaluated a standing armrest to provide more acceptable ergonomic guidelines that may reduce the cost of standing computer workstations. Background Of the many advantages of standing workstations, there have been no efforts to minimize the biomechanical cost, such as larger wrist extension and greater forearm muscle activity than sitting. Method Sixteen participants were asked to perform a typing task under a combination of the following factors: (1) desk shape (rectangular and concave); (2) desk height (0, +5, -5 cm from 90° elbow flexion); and (3) monitor height (0, −10 cm from the eyes). During the trials, the trunk kinematics, muscle activation levels, and CoP were recorded. Results Both arms were further away from the upper body under the concave and +5 desk height than under the normal condition, but significant decreases in the extensor carpi radialis (8.6%), anterior deltoid (28.8%), and L4 paraspinals (5.5%) were observed. Similarly, the wrist extension angle decreased by 10.5° (42%) under this condition, but the posture required a 2.2° (19%) increase in wrist adduction angle. The CoP irregularity was greater under the concave workstation, indicating more complex motion. Conclusion A higher and concave desk can provide an armrest effect while engaged in a standing workstation by reducing the wrist extension and related muscle activation level, but at the cost of a larger wrist adduction angle. Application Providing a standing armrest (+5 cm height and concave desk) could reduce the stresses on the upper extremities, but a split keyboard should be considered to minimize wrist adduction.

Objective This study examined a system-level perspective to investigate the changes in the whole trunk and head postures while sitting with various lower extremity postures. Background Sitting biomechanics has focused mainly on the lumbar region only, whereas the anatomy literature has suggested various links from the head and lower extremity. Method Seventeen male participants were seated in six lower extremity postures, and the trunk kinematics and muscle activity measures were captured for 5 s. Results Changes in the trunk-thigh angle and the knee angle affected the trunk and head postures and muscle recruitment patterns significantly, indicating significant interactions between the lower extremity and trunk while sitting. Specifically, the larger trunk-thigh angle (T135°) showed more neutral lumbar lordosis (4.0° on average), smaller pelvic flexion (1.8°), smaller head flexion (3.3°), and a less rounded shoulder (1.7°) than the smaller one (T90°). The smaller knee angle (K45°) revealed a more neutral lumbar lordosis (6.9°), smaller pelvic flexion (9.2°), smaller head flexion (2.6°), and less rounded shoulder (2.4°) than the larger condition (K180°). The more neutral posture suggested by the kinematic measures confirmed significantly less muscular recruitment in the trunk extensors, except for a significant antagonistic co-contraction. Conclusion The lower and upper back postures were more neutral, and back muscle recruitment was lower with a larger trunk-thigh angle and a smaller knee angle, but at the cost of antagonistic co-contraction. Application The costs and benefits of each lower extremity posture can be used to design an ergonomic chair and develop an improved sitting strategy.

No abstract