Development of a usability evaluation method using natural product-use motion

A Study on sEMG-Based Motor Variability and Functional Connectivity of the Upper Limb Depending on Weight Distributions in a Handle of a Cordless Stick-Type Vacuum Cleaner

This study investigated the muscle activities, motor variability, and functional connectivity of the upper limb as a function of weight distributions in a handle of a cordless stick-type vacuum cleaner. Eighteen female college students with experience of vacuum cleaner-use participated in testing. Five handles with different centers of mass (CM) were prepared (centroid, top-rear, top-front, bottom-front, and bottom-rear), and electromyography for the muscles of the upper limb were measured during vacuuming. The results showed that the %MVC values of the Extensor Carpi Ulnaris (p = 0.0038) and Deltoid Middle (p = 0.0094) increased but that of the Biceps Brachii (p = 0.0001) decreased, as the CM moved from the top to bottom area of the handle. The motor variability of the Extensor Carpi Ulnaris (p = 0.0335) and Brachioradialis (p = 0.0394) significantly varied depending on the CM locations but failed to show significance in the post-hoc analyses. Lastly, the functional connectivity values of the muscle pairs such as the Extensor Carpi Ulnaris–Deltoid Middle (p = 0.0016), Extensor Carpi Ulnaris–Upper Trapezius (p = 0.0174), Brachioradialis–Biceps Brachii (p = 0.0356), and Biceps Brachii–Upper Trapezius (p = 0.0102) were significantly altered as a function of the CM locations. The lowest functional connectivity was found with the handle of which CM was at centroid.

The movement profile of trunk and neck during habitual vacuuming

Musculoskeletal disorders of the trunk and neck are common among cleaners. Vacuum cleaning is a demanding activity. The aim of this study was to present the movement profile of the trunk and neck during habitual vacuuming. The data were collected from 31 subjects (21f./10 m) using a 3D motion analysis system (Xsens). 10 cycles were analysed in vacuuming PVC and carpet floors with 8 vacuum cleaners. The joint angles and velocities were represented statistically descriptive. When vacuuming, the trunk is held in a forwardly inclined position by a flexion in the hip and rotated from this position. In the joint angles and velocities of the spine, the rotation proved to be dominant. A relatively large amount of movement took place in the cervical spine and also in the lumbar spine. The shown movement profile is rather a comfort area of vacuuming which may serve as a reference for ergonomics in vacuuming.

The Movement Profile of Habitual Vacuuming as a Cyclic Movement-A Pilot Study

Background: Vacuum cleaning, which is associated with musculoskeletal complaints, is frequently carried out in private households and by professional cleaners. The aim of this pilot study was to quantify the movements during habitual vacuuming and to characterize the movement profile with regard to its variability. Methods: The data were collected from 31 subjects (21 f/10 m) using a 3D motion analysis system (XSens). Eight vacuum cleaners were used to vacuum polyvinyl chloride (PVC) and carpet floors. In 15 joints of the right upper extremity, the trunk and the lower extremities, Principal Component Analysis was used to determine the predominantly varying joints during vacuuming. Results: The movements of the trunk and the lower extremities were relatively constant and, therefore, had less influence. The shoulder, elbow and wrist joints were identified as joints that can be decisive for the movement profile and that can be influenced. These joints were represented in the course of the vacuuming cycle by the mean movement with its standard deviation. Conclusion: In summary, the generalization of a movement profile is possible for the trunk and the lower extremities due to the relative homogeneity. In future it will be necessary to identify factors influencing variability in order to draw conclusions about movement ergonomics.

Analysis of natural finger-press motions for design of trackball buttons

This study analysed natural press motions of the index, middle and ring fingers for ergonomic design of the positions and surface angles of the left, middle and right trackball buttons. Finger motions of 26 male participants for naturally pressing the trackball buttons were recorded after the participants adjusted the trackball buttons to their preferred locations for comfortable pressing. The natural positions of the finger pulps formed a symmetrically rainbow-shaped reach zone for the fingers. The natural press angles of the fingers' motion trajectories to the vertical reference line ranged from 14.2° to 20.5°, suggesting an 18-degree surface from the horizontal line for the trackball buttons. Regression formulas (adjusted R² = 0.90 ± 0.07 and mean squared error = 8.55 ± 7.52 mm) were established to estimate the natural positions of finger pulps from hand segment lengths and joint angles for a population having different hand sizes from this study. Relevance to industry.

Effects of the center of mass of a stick vacuum cleaner on the muscle activities of the upper extremity during floor vacuuming

Cordless stick vacuum cleaners on the market have two distinctive styles. One with the center of mass (CoM) near user's hand and the other with the CoM near the brush. The main objective of this study was to determine whether the CoM would affect the muscle activities of upper extremity during floor vacuuming. Twenty-four participants conducted floor vacuuming strokes on carpeted floor and tiled floor at two different speeds with a 2.57 kg stick cleaner model with the CoM near its handle and near its brush. The 50^th %-ile muscle activities ranged from 5.4% to 16.3% of the maximum activity level (mild to moderate intensity), with significantly greater activities (p < 0.05) when vacuuming with the high CoM model. Study results suggest that conventional low CoM stick cleaners are preferable to high CoM stick cleaners to lower physical loads to user's upper extremity muscles for floor vacuuming.

Influence of folding mechanism of bicycles on their usability

In this study, foldable bicycles were evaluated in terms of their usability. Four types of folding mechanisms were identified depending on the number of pivots and the pivot axis direction: single lateral pivot (SLP), single vertical pivot, dual lateral pivot, and combined vertical-lateral pivot. Next, four bicycles-one each of these four types-were selected as test specimens. Ten subjects performed folding and unfolding tasks on each of these bicycles, and three-dimensional body motions and ground reaction forces were measured. The maximum trunk flexion angles and maximum increments in the ground reaction force were used as governing parameters for evaluating the comfort level for each bicycle type. The SLP type provided the lowest upper body flexion and ground reaction force and was hence judged to be the most comfortable folding system. Hence, a promising type of easily foldable bicycle was proposed, thereby encouraging its incorporation into public transit systems.

Development of a press and drag method for hyperlink selection on smartphones

The present study developed a novel touch method for hyperlink selection on smartphones consisting of two sequential finger interactions: press and drag motions. The novel method requires a user to press a target hyperlink, and if a touch error occurs he/she can immediately correct the touch error by dragging the finger without releasing it in the middle. The method was compared with two existing methods in terms of completion time, error rate, and subjective rating. Forty college students participated in the experiments with different hyperlink sizes (4-pt, 6-pt, 8-pt, and 10-pt) on a touch-screen device. When hyperlink size was small (4-pt and 6-pt), the novel method (time: 826 msec; error: 0.6%) demonstrated better completion time and error rate than the current method (time: 1194 msec; error: 22%). In addition, the novel method (1.15, slightly satisfied, in 7-pt bipolar scale) had significantly higher satisfaction scores than the two existing methods (0.06, neutral).