Matthieu B. Trudeau

Touch-screen tablet user configurations and case-supported tilt affect head and neck flexion angles.

OBJECTIVE The aim of this study was to determine how head and neck postures vary when using two media tablet (slate) computers in four common user configurations. METHODS Fifteen experienced media tablet users completed a set of simulated tasks with two media tablets in four typical user configurations. The four configurations were: on the lap and held with the users hands, on the lap and in a case, on a table and in a case, and on a table and in a case set at a high angle for watching movies. An infra-red LED marker based motion analysis system measured head/neck postures. RESULTS Head and neck flexion significantly varied across the four configurations and across the two tablets tested. Head and neck flexion angles during tablet use were greater, in general, than angles previously reported for desktop and notebook computing. Postural differences between tablets were driven by case designs, which provided significantly different tilt angles, while postural differences between configurations were driven by gaze and viewing angles. CONCLUSION Head and neck posture during tablet computing can be improved by placing the tablet higher to avoid low gaze angles (i.e. on a table rather than on the lap) and through the use of a case that provides optimal viewing angles.

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°/s2). 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.

Thumb motor performance varies by movement orientation, direction, and device size during single-handed mobile phone use.

Objective: The aim of this study was to determine if thumb motor performance metrics varied by movement orientation, direction, and device size during single-handed use of a mobile phone device. Background: With the increased use of mobile phones, understanding how design factors affect and improve performance can provide better design guidelines. Method: A repeated measures laboratory experiment of 20 right-handed participants measured the thumb tip’s 3-D position relative to a phone during reciprocal tapping tasks across four phone designs and four thumb tip movement orientations. Each movement orientation included two movement directions: an “outward” direction consisting in CMC (carpometacarpal) joint flexion or abduction movements and an “inward” direction consisting in CMC joint extension or adduction movements. Calculated metrics of the thumb’s motor performance were Fitts’ effective width and index of performance. Results: Index of performance varied significantly across phones, with performance being generally better for the smaller devices. Performance was also significantly higher for adduction–abduction movement orientations compared to flexion–extension, and for “outward” compared to “inward” movement directions. Conclusion: For single-handed device use, adduction–abduction-type movements on smaller phones lead to better thumb performance. Application: The results from this study can be used to design new mobile phone devices and keypad interfaces that optimize specific thumb motions to improve the user-interface experience during single-handed use.

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.

Biomechanical loading on the upper extremity increases from single key tapping to directional tapping

Musculoskeletal disorders associated with computer use span the joints of the upper extremity. Computing typically involves tapping in multiple directions. Thus, we sought to describe the loading on the finger, wrist, elbow and shoulder joints in terms of kinematic and kinetic difference across single key switch tapping to directional tapping on multiple keys. An experiment with repeated measures design was conducted. Six subjects tapped with their right index finger on a stand-alone number keypad placed horizontally in three conditions: (1) on single key switch (the number key 5); (2) left and right on number key 4 and 6; (3) top and bottom on number key 8 and 2. A force-torque transducer underneath the keypad measured the fingertip force. An active-marker infrared motion analysis system measured the kinematics of the fingertip, hand, forearm, upper arm and torso. Joint moments for the metacarpophalangeal, wrist, elbow, and shoulder joints were estimated using inverse dynamics. Tapping in the top-bottom orientation introduced the largest biomechanical loading on the upper extremity especially for the proximal joint, followed by tapping in the left-right orientation, and the lowest loading was observed during single key switch tapping. Directional tapping on average increased the fingertip force, joint excursion, and peak-to-peak joint torque by 45%, 190% and 55%, respectively. Identifying the biomechanical loading patterns associated with these fundamental movements of keying improves the understanding of the risks of upper extremity musculoskeletal disorders for computer keyboard users.

Assessing Footwear Effects from Principal Features of Plantar Loading during Running

PURPOSE The effects of footwear on the musculoskeletal system are commonly assessed by interpreting the resultant force at the foot during the stance phase of running. However, this approach overlooks loading patterns across the entire foot. An alternative technique for assessing foot loading across different footwear conditions is possible using comprehensive analysis tools that extract different foot loading features, thus enhancing the functional interpretation of the differences across different interventions. The purpose of this article was to use pattern recognition techniques to develop and use a novel comprehensive method for assessing the effects of different footwear interventions on plantar loading. METHODS A principal component analysis was used to extract different loading features from the stance phase of running, and a support vector machine (SVM) was used to determine whether and how these loading features were different across three shoe conditions. RESULTS The results revealed distinct loading features at the foot during the stance phase of running. The loading features determined from the principal component analysis allowed successful classification of all three shoe conditions using the SVM. Several differences were found in the location and timing of the loading across each pairwise shoe comparison using the output from the SVM. CONCLUSIONS The analysis approach proposed can successfully be used to compare different loading patterns with a much greater resolution than has been reported previously. This study has several important applications. One such application is that it would not be relevant for a user to select a shoe or for a manufacturer to alter a shoes construction if the classification across shoe conditions would not have been significant.

Thumb Motor Performance is Greater for Two-Handed Grip Compared to Single-Handed Grip on a Mobile Phone

The aim of this study was to determine if thumb motor performance varied between singlehanded and two-handed grip for thumb tapping tasks on a mobile phone. A secondary aim was to determine if differences in phone movement variation and thumb flexion could account for variations in motor performance across the two grip configurations. Ten right-handed participants (5 males, 5 females) completed reciprocal thumb tapping tasks on an Apple iPhone 3® in a single-handed and a two-handed grip configuration while an active-marker motion capture system measured 3D kinematics of the thumb and phone. The results show that thumb motor performance was significantly greater for the two-handed grip configuration due to less phone movement variation compared to the single-handed grip configuration. Thumb flexion did not significantly vary across configurations. These data suggest that increasing support for the phone such as by using a two-handed grip could lead to increases in tapping performance. For example, increased performance would be expected when using phones that include a landscape mode and are wide enough to allow a stable two-handed grip.

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 dorsiflexion 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. Conclusions 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.

Intra-rater reliability of footwear-related comfort assessments

Comfort is an important aspect of athletic footwear since it has been associated with health and performance benefits. Footwear comfort is also a key consideration in orthotic therapy during the prescription/fitting process of foot orthoses. However, little is known about the actual ability of individuals to reliably assess footwear-related comfort. Therefore, the main objective of this study was to determine the intra-rater reliability of footwear comfort assessments. Ninety healthy male adults completed one familiarization and two testing sessions on different days. During each session, participants performed running trials to assess comfort of six different shoe insoles using Visual Analog Scales (VASs) and Yes–No questions. For the VAS, intra-rater reliability was determined using intra-class correlation coefficients. Cronbachs alpha was calculated to obtain the intra-rater reliability based on the Yes–No questions. For 31.1% of the participants a reliable assessment based on the VAS (intra-class correlation coefficient ≥ 0.7) was obtained. Using Yes–No questions (Cronbachs alpha ≥ 0.7), 46.7% of the participants had a reliable comfort assessment. The majority of individuals did not seem able to reliably assess footwear comfort, and the reason for this poor reliability remains unclear. However, when using footwear comfort in orthotic therapy, scientific research projects, or footwear development one should account for this low reliability of comfort assessments. This may be done by (1) simplifying the measure used to assess comfort, (2) only selecting individuals that were pre-tested for reliable assessments, and/or (3) establishing mean comfort ratings for an individual across multiple testing sessions.

How reliable are subjective footwear comfort assessments

Bishop, C. et al. (2015). A method to investigate the effect of shoe-hole size on surface marker movement when describing in-shoe joint kinematics using a multi-segment foot model. Gait & Posture, 41(1), 295 299. Hill, C. et al. (2008). Journal of Foot and Ankle Research, 1(2), 1 7. Lee, S. et al. (2009). Does the use of orthoses improve selfreported pain and function measures in patients with plantar fasciitis? A meta-analysis. Physical Therapy in Sport, 10(1), 12 18.