Biomedical subjects

Jack T Dennerlein

Publications and source records attributed to Jack T Dennerlein.

10 recordsLinked to original sources

PubMed2006

Changes in upper extremity biomechanics across different mouse positions in a computer workstation.

In order to determine differences in biomechanical risk factors across different mouse positions within computer workstations a repeated measures laboratory study was completed with 30 adults (15 females 15 males). The subjects performed mouse-intensive tasks during two experiments. One experiment examined three mouse positions: a standard mouse (SM) position with the mouse directly to the right of the keyboard; a central mouse (CM) position with the mouse between the keyboard and the body, positioned in the body's mid-sagittal plane; a high mouse (HM) position, which simulated using a keyboard drawer with the mouse on the primary work surface. The second experiment compared two mouse positions: the SM position and a more central position using a keyboard without a number keypad (NM). Electrogoniometers and inclinometers measured wrist and upper arm postures and surface electromyography measured muscle activity of four forearm muscles and three shoulder muscles. The CM mouse position was found to produce the most neutral upper extremity posture across all measures. The HM position produced the least neutral posture and resulted in the highest level of muscle activity. Compared to the SM position, the NM position reduced wrist extension slightly and promoted a more neutral shoulder posture. Little difference in muscle activity was observed between the SM and NM positions. In conclusion, of these alternative mouse positions, the HM position was the least desirable, whereas the CM position reduced overall awkward postures associated with mouse-intensive computer tasks.

Adult↗

PubMed2006

Prevalence and physical determinants of low back pain in a rural Chinese population.

STUDY DESIGN: This was a community-based cross-sectional study that is part of an ongoing study of genetics and osteoporosis. OBJECTIVES: To estimate the 1-year self-reported prevalence of low back pain (LBP); and to assess the association between physical exposures (occupation, physical stress, and vibration) and LBP in a rural Chinese population. This study also explored how these associations change when individuals with LBP report additional pains in other parts of the body. SUMMARY OF BACKGROUND DATA: Little is known about the prevalence and determinants of LBP in rural developing populations, even though approximately half of the world's population, mostly from the developing world, is engaged in agriculture, a known strenuous activity. METHODS: Families with at least three participating siblings residing in the surrounding rural region of Anqing city, Anhui Province, China, were invited to participate in the study through public announcements and direct invitations by village physicians. A questionnaire including demographics, physical exposures, and musculoskeletal pain was administered to 13,965 men and women (age, 25-64 years). Generalized estimating equations were used to estimate LBP prevalence and examine associations between LBP and physical exposures. RESULTS: The 1-year prevalence of LBP was 64%. Twenty-five percent reported no pain at any body site. Women had higher prevalence of LBP than men across all age groups. Being a farmer, reporting moderate or heavy physical stress, and having had former or current exposures to vibration were positively associated with LBP (P < 0.05). Physical exposures were also associated with cases of LBP combined with other musculoskeletal pains, and generally, the more pains individuals reported, the more likely it was that they were farmers and were exposed to vibration. CONCLUSION: A high prevalence of LBP and LBP with additional musculoskeletal pain existed in this rural Chinese sample. We found evidence of a link between physical exposures and LBP, and LBP with additional musculoskeletal pain. Further understanding of the characteristics and risk factors of LBP in rural developing areas is needed.

Adult↗

PubMed2006

Different computer tasks affect the exposure of the upper extremity to biomechanical risk factors.

In order to determine differences in biomechanical risk factors across computer tasks, a repeated measures laboratory experiment was completed with 30 touch-typing adults (15 females and 15 males). The participants completed five different computer tasks: typing text, completing an html-based form with text fields, editing text within a document, sorting and resizing objects in a graphics task and browsing and navigating a series of intranet web pages. Electrogoniometers and inclinometers measured wrist and upper arm postures, surface electromyography measured muscle activity of four forearm muscles and three shoulder muscles and a force platform under the keyboard and force-sensing computer mouse measured applied forces. Keyboard-intensive tasks were associated with less neutral wrist postures, larger wrist velocities and accelerations and larger dynamic forearm muscle activity. Mouse-intensive tasks (graphics and intranet web page browsing) were associated with less neutral shoulder postures and less variability in forearm muscle activity. Tasks containing a mixture of mouse and keyboard use (form completion and text editing) were associated with higher shoulder muscle activity, larger range of motion and larger velocities and accelerations of the upper arm. Comparing different types of computer work demonstrates that mouse use is prevalent in most computer tasks and is associated with more constrained and non-neutral postures of the wrist and shoulder compared to keyboarding.

Adult↗

PubMed2006

Keyswitch orientation can reduce finger joint torques during tapping on a computer keyswitch.

OBJECTIVE: To examine the effects of keyswitch orientation on joint torques. BACKGROUND: The fingertip produces primarily vertical forces during single-finger tapping on a computer keyswitch. However, horizontal force components within the sagittal plane of the finger could reduce net joint torques. METHOD: Eleven participants tapped on a keyswitch oriented in three directions: vertical, tilted 30 degrees such that when pressed it moved away from the user (similar to a positive-tilt keyboard), and tilted 30 degrees such that when pressed it moved toward the user (similar to a negative-tilt keyboard). Participants also tapped on a prototype cantilever keyswitch design in which the key cap moves along the arc of a bending beam gradually away from the user. Miniature electro-optical goniometers measured the finger posture, and a two-axis force sensor measured fingertip forces. RESULTS: Tapping on a keyswitch oriented such that it moves away from the user when pressed reduced net joint torques by 47% relative to tapping on a vertically orientated keyswitch and by 56% relative to tapping on a keyswitch oriented toward the user, whereas the cantilever design resulted in 14% decreases in net joint torque relative to the vertical orientation. CONCLUSION: Reductions of torques resulted from decreasing the moment arm of the fingertip force about the joints. APPLICATION: Keyboard design should incorporate keyswitch mechanism angles along with other postural and geometric constraints to reduce exposure of the finger joints and muscles to force during typing.

Adult↗

PubMed2006

Forearm electromyographic changes with the use of a haptic force-feedback computer mouse.

OBJECTIVE: To examine changes in biomechanical and motor control associated with a force-feedback computer mouse. BACKGROUND: Haptic computer mice can improve the movement times for point-and-click tasks; however, changes in upper extremity biomechanics and motor control are unknown. METHOD: Eighteen people (ages 22-37 years) performed a point-and-click task 80 times using a force-feedback computer mouse across three different conditions: (a) no force feedback, emulating a conventional mouse; (b) a single attractive force field at the desired target that pulls the mouse to the center of the target; and (c) an attractive force field at the desired target as well as others between the two possible targets, distracting the user from the intended target. Cursor kinematics, wrist posture, and electromyographic (EMG) forearm muscle activity were recorded. RESULTS: The point-and-click movements were 30% faster with the addition of a single force field and 3% faster with the addition of multiple force fields. The Fitts' law index of performance metrics improved from 2.9 bits/response to 4.1 bits/response for multiple attractive fields and to 6.0 bits/response for a single force field. For the distracting force fields, the cursor maximum velocities were over 50% faster. EMG amplitude values were largest for the distracting force fields. These data suggest that the operator uses increased muscle activity to accelerate the mouse through the distracting force fields. CONCLUSION: When implementing attractive haptic force fields, one needs to consider how to reduce these observed effects of potential distracting force fields. APPLICATION: Applications include human-computer interface design for pointing devices extensively used for the graphical user interface.

Adult↗

PubMed2005

Finger joint coordination during tapping.

We investigated finger joint coordination during tapping by characterizing joint kinematics and torques in terms of muscle activation patterns and energy profiles. Six subjects tapped with their index finger on a computer keyswitch as if they were typing on the middle row of a keyboard. Fingertip force, keyswitch position, kinematics of the metacarpophalangeal (MCP) and the proximal and distal interphalangeal (IP) joints, and intramuscular electromyography of intrinsic and extrinsic finger muscles were measured simultaneously. Finger joint torques were calculated based on a closed-form Newton-Euler inverse dynamic model of the finger. During the keystroke, the MCP joint flexed and the IP joints extended before and throughout the loading phase of the contact period, creating a closing reciprocal motion of the finger joints. As the finger lifted, the MCP joint extended and the interphalangeal (IP) joints flexed, creating an opening reciprocal motion. Intrinsic finger muscle and extrinsic flexor activities both began after the initiation of the downward finger movement. The intrinsic finger muscle activity preceded both the IP joint extension and the onset of extrinsic muscle activity. Only extrinsic extensor activity was present as the finger was lifted. While both potential energy and kinetic energy are present and large enough to overcome the work necessary to press the keyswitch, the motor control strategies utilize the muscle forces and joint torques to ensure a successful keystroke.

Adult↗

PubMed2004

Effects of keyswitch design and finger posture on finger joint kinematics and dynamics during tapping on computer keyswitches.

OBJECTIVE: To examine the effects of postural and keyswitch characteristics on musculoskeletal tissue loading during tapping on computer keyswitches. DESIGN: We hypothesized that joint torques, stiffness and work parameters differ across keyswitch designs and finger postures typical of those observed during computer keyboard typing. We experimentally measured joint kinematics and calculated joint torques while tapping on different keyswitches in different postures, and analyzed the data using mechanical impedance models. METHODS: Sixteen human subjects tapped with the index finger on computer keyswitches mounted on a sensor which measured vertical and horizontal forces. Miniature electro-optical goniometers mounted dorsally across each finger joint measured joint kinematics. Joint torques were calculated from endpoint forces and joint kinematics using an inverse dynamics algorithm. A linear spring-damper impedance model was fitted to joint torque, position, and velocity during the contact period of each tap. Subjects tapped in three postures approximating those employed during tapping on three rows of a computer keyboard, on four different keyswitches, resulting in 12 conditions. RESULTS: More extended finger posture was associated with greater joint torques, energies, and stiffnesses, despite minimal differences in endpoint forces across posture. Greater keyswitch make forces were associated with increased forces, joint torques and joint stiffnesses, however this relationship was not monotonic. CONCLUSIONS: Joint torques and stiffness parameters differed across keyswitch designs and finger postures. Estimates of joint impedance and work provided a unique perspective into finger dynamics. RELEVANCE: Determining the causes of work-related musculoskeletal disorders is facilitated by characterizing workplace task biomechanics, which can be linked to specific injury mechanisms.

Adult↗

PubMed2004

Finger joint impedance during tapping on a computer keyswitch.

We studied the dynamic behavior of finger joints during the contact period of tapping on a computer keyswitch, to characterize and parameterize joint function with a lumped-parameter impedance model. We tested the hypothesis that the metacarpophalangeal (MCP) and interphalangeal (IP) joints act similarly in terms of kinematics, torque, and energy production when tapping. Fifteen human subjects tapped with the index finger of the right hand on a computer keyswitch mounted on a two-axis force sensor, which measured forces in the vertical and sagittal planes. Miniature fiber-optic goniometers mounted across the dorsal side of each joint measured joint kinematics. Joint torques were calculated from endpoint forces and joint kinematics using an inverse dynamic algorithm. For each joint, a linear spring and damper model was fitted to joint torque, position, and velocity during the contact period of each tap (22 per subject on average). The spring-damper model could account for over 90% of the variance in torque when loading and unloading portions of the contact were separated, with model parameters comparable to those previously measured during isometric loading of the finger. The finger joints functioned differently, as illustrated by energy production during the contact period. During the loading phase of contact the MCP joint flexed and produced energy, whereas the proximal and distal IP joints extended and absorbed energy. These results suggest that the MCP joint does work on the interphalangeal joints as well as on the keyswitch.

Adult↗

PubMed2004

Using exposure prediction rules for exposure assessment: an example on whole-body vibration in taxi drivers.

BACKGROUND: It is often difficult and expensive to make direct measurements of an individual's occupational or environmental exposures in large epidemiologic studies. METHODS: In this study, we used information collected in validation studies to develop a prediction rule for assessing exposure in a study with no direct measurement. We established a prediction rule through mixed-effect modeling of direct measurement data and information on observable exposure predictors and their interactions. Specifically, we used 383 measures of whole-body vibration from 247 professional taxi drivers and attempted to quantify vibration exposures for individuals in a large study on low back pain. RESULTS: Using the "jackknife method," we found that our prediction rule had an acceptably low relative prediction error of 11% (95% confidence interval-10-12%). Implementing the prediction rule would result in measurement errors independent of low back pain and of all identified and observable predictors of whole-body vibration. We applied the predicted levels to compute each person's daily exposure, and found a strong association between the predicted daily whole-body vibration exposure and prevalence of low back pain. This supported the construct validity of the exposure prediction rule. CONCLUSIONS: The predictive and construct validity of our prediction rule suggests that this general statistical approach can be useful in other occupational settings to improve the quality of exposure assessment.

Adult↗

PubMed2004

Knee pain and driving duration: a secondary analysis of the Taxi Drivers' Health Study.

OBJECTIVES: We explored a postulated association between daily driving time and knee pain. METHODS: We used data from the Taxi Drivers' Health Study to estimate 1-year prevalence of knee pain as assessed by the Nordic musculoskeletal questionnaire. RESULTS: Among 1242 drivers, the prevalence of knee pain, stratified by duration of daily driving (< or = 6, > 6 through 8, > 8 through 10, and > 10 hours), was 11%, 17%, 19%, and 22%, respectively. Compared with driving 6 or fewer hours per day, the odds ratio of knee pain prevalence for driving more than 6 hours per day was 2.52 (95% confidence interval = 1.36, 4.65) after we adjusted for socioeconomic, work-related, and personal factors in the multiple logistic regression. CONCLUSIONS: The dose-related association between driving duration and knee pain raises concerns about work-related knee joint disorders among professional drivers.

Absenteeism↗