A Data-Driven Design Evaluation Tool for Handheld Device Soft Keyboards

Thumb interaction is a primary technique used to operate small handheld devices such as smartphones. Despite the different techniques involved in operating a handheld device compared to a personal computer, the keyboard layouts for both devices are similar. A handheld device keyboard that considers the physical capabilities of the thumb may improve user experience. We developed and applied a design evaluation tool for different geometries of the QWERTY keyboard using a performance evaluation model. The model utilizes previously collected data on thumb motor performance and posture for different tap locations and thumb movement directions. We calculated a performance index (PITOT, 0 is worst and 2 is best) for 663 designs consisting in different combinations of three variables: the keyboard's radius of curvature (R) (mm), orientation (O) (°), and vertical location on the screen (L). The current standard keyboard performed poorly (PITOT = 0.28) compared to other designs considered. Keyboard location (L) contributed to the greatest variability in performance out of the three design variables, suggesting that designers should modify this variable first. Performance was greatest for designs in the middle keyboard location. In addition, having a slightly upward curve (R = −20 mm) and orientated perpendicular to the thumb's long axis (O = −20°) improved performance to PITOT = 1.97. Poorest performances were associated with placement of the keyboard's spacebar in the bottom right corner of the screen (e.g., the worst was for R = 20 mm, O = 40°, L = Bottom (PITOT = 0.09)). While this evaluation tool can be used in the design process as an ergonomic reference to promote user motor performance, other design variables such as visual access and usability still remain unexplored

Tablet Keyboard Configuration Affects Performance, Discomfort and Task Difficulty for Thumb Typing in a Two-Handed Grip

When holding a tablet computer with two hands, the touch keyboard configuration imposes postural constraints on the user because of the need to simultaneously hold the device and type with the thumbs. Designers have provided users with several possible keyboard configurations (device orientation, keyboard layout and location). However, potential differences in performance, usability and postures among these configurations have not been explored. We hypothesize that (1) the narrower standard keyboard layout in the portrait orientation leads to lower self-reported discomfort and less reach than the landscape orientation; (2) a split keyboard layout results in better overall outcomes compared to the standard layout; and (3) the conventional bottom keyboard location leads to the best outcomes overall compared to other locations. A repeated measures laboratory experiment of 12 tablet owners measured typing speed, discomfort, task difficulty, and thumb/wrist joint postures using an active marker system during typing tasks for different combinations of device orientation (portrait and landscape), keyboard layout (standard and split), and keyboard location (bottom, middle, top). The narrower standard keyboard with the device in the portrait orientation was associated with less discomfort (least squares mean (and S.E.) 2.9±0.6) than the landscape orientation (4.5±0.7). Additionally, the split keyboard decreased the amount of reaching required by the thumb in the landscape orientation as defined by a reduced range of motion and less MCP extension, which may have led to reduced discomfort (2.7±0.6) compared to the standard layout (4.5±0.7). However, typing speed was greater for the standard layout (127±5 char./min.) compared to the split layout (113±4 char./min.) regardless of device orientation and keyboard location. Usage guidelines and designers can incorporate these findings to optimize keyboard design parameters and form factors that promote user performance and usability for thumb interaction

The preferred movement path paradigm: influence of running shoes on joint movement

PURPOSE: (a) to quantify differences in lower extremity joint kinematics for groups of runners subjected to different running footwear conditions, and (b) to quantify differences in lower extremity joint kinematics on an individual basis for runners subjected to different running footwear conditions. METHODS: Three-dimensional ankle and knee joint kinematics were collected for 35 heel-toe runners when wearing three different running shoes and when running barefoot. Absolute mean differences in ankle and knee joint kinematics were computed between running shoe conditions. The percentage of individual runners who displayed differences below a 2°, 3° and 5° threshold were also calculated. RESULTS: The results indicate that the mean kinematics of the ankle and knee joints were similar between running shoe conditions. Aside from ankle dorsi-flexion and knee flexion, the percentage of runners maintaining their movement path between running shoes (i.e. less than 3°) was in the order of magnitude of about 80 to 100%. Many runners showed ankle and knee joint kinematics that differed between a conventional running shoe and barefoot by more than 3°, especially for ankle dorsiflexion and knee flexion CONCLUSION: Many runners stay in the same movement path (the preferred movement path) when running in various different footwear conditions. The percentage of runners maintaining their preferred movement path depends on the magnitude of the change introduced by the footwear condition

Effects of forearm and palm supports on the upper extremity during computer mouse use

The use of forearm and palm supports has been associated with lower neck and shoulder muscle activity as well as reduced musculoskeletal discomfort during keyboard use, however, few studies have investigated their effect during computer mouse use. Eight men and eight women completed several computer mousing tasks in six arm support conditions: Forearm Support, Flat Palm Support, Raised Palm Support, Forearm + Flat Palm Support, Forearm + Raised Palm Support, and No Support. Concurrently, an infrared three-dimensional motion analysis system measured postures, six-degree-of-freedom force-torque sensors measured applied forces & torques, and surface electromyography measured muscle activity. The use of forearm support compared to the no support condition was significantly associated with less shoulder muscle activity & torque, and the raised palm support was associated with less wrist extension. Forearm supports reduced shoulder flexion torque by 90% compared to no support. The use of either support also resulted in lower applied forces to the mouse pad. Participants reported less musculoskeletal discomfort when using a support. These results provide recommendations for office workstation setup and inform ergonomists of effective ways to reduce musculoskeletal exposures

Wrist and shoulder posture and muscle activity during touch-screen tablet use: Effects of usage configuration, tablet type, and interacting hand

BACKGROUND: Due to its rapid growth in popularity, there is an imminent need for ergonomic evaluation of the touch-screen tablet computing form-factor. OBJECTIVE: The aim of this study was to assess postures of the shoulders and wrists and their associated muscle activity during touch-screen tablet use. METHODS: Fifteen experienced adult tablet users completed a set of simulated software tasks on two media tablets in a total of seven user configurations. Configurations consisted of a combination of a support condition (held with one hand, two hands or in a case), a location (on the lap or table surface), and a software task (web browsing, email, and game). Shoulder postures were measured by using an infra-red LED marker based motion analysis system, wrist postures by electro-goniometry, and shoulder (upper trapezius and anterior deltoid) and forearm (flexor carpi radialis, flexor carp ulnaris, and extensor radialis) muscle activity by surface electromyography. RESULTS: Postures and muscle activity for the wrist significantly varied across configurations and between hands, but not across the two tablets tested. Wrist extension was high for all configurations and particularly for the dominant hand when a tablet was placed on the lap (mean=38°). Software tasks involving the virtual keyboard (e-mailing) corresponded to higher wrist extensor muscle activity (50th percentile=9.5% MVC) and wrist flexion/extension acceleration (mean=322°/s^{2}). High levels of wrist radial deviation were observed for the non-dominant hand when it was used to tilt and hold the tablet (mean=13°). Observed differences in posture and muscle activity of the shoulder were driven by tablet location. CONCLUSION: Touch-screen tablet users are exposed to extreme wrist postures that are less neutral than other computing technologies and may be at greater risk of developing musculoskeletal symptoms. Tablets should be placed in cases or stands that adjust the tilt of the screen rather than supporting and tilting the tablet with only one hand

The habitual motion path theory: Evidence from cartilage volume reductions in the knee joint after 75 minutes of running

The habitual motion path theory predicts that humans tend to maintain their habitual motion path (HMP) during locomotion. The HMP is the path of least resistance of the joints defined by an individual's musculoskeletal anatomy and passive tissue properties. Here we tested whether participants with higher HMP deviation and whether using footwear that increases HMP deviation during running show higher reductions of knee joint articular cartilage volume after 75 minutes of running. We quantified knee joint articular cartilage volumes before and after the run using a 3.0-Tesla MRI. We performed a 3D movement analysis of runners in order to quantify their HMP from a two-legged squat motion and the deviation from the HMP when running in different footwear conditions. We found significantly more cartilage volume reductions in the medial knee compartment and patella for participants with higher HMP deviation. We also found higher cartilage volume reductions on the medial tibia when runners wore a shoe that maximized their HMP deviation compared with the shoe that minmized their HMP deviation. Runners might benefit from reducing their HMP deviation and from selecting footwear by quantifying HMP deviation in order to minimize joint cartilage loading in sub-areas of the knee

Keyboard configurations.

<p>The 11 different configurations involved different combinations of the following 3 independent variables: (a) 2 device orientations, (b) 2 keyboard layouts, and (c) 3 keyboard locations.</p