Biomedical subjects

Aruna D Balakrishnan

Publications and source records attributed to Aruna D Balakrishnan.

3 recordsLinked to original sources

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↗

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↗