title: Effects of keyswitch design and finger posture on finger joint kinematics and dynamics during tapping on computer keyswitches.
abstract: OBJECTIVE
  To examine the effects of postural and keyswitch characteristics on musculoskeletal tissue loading during tapping on computer keyswitches.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  Determining the causes of work-related musculoskeletal disorders is facilitated by characterizing workplace task biomechanics, which can be linked to specific injury mechanisms.
authors.affiliation: Department of Environmental Health, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA.
authors.forename: Devin L
authors.initials: DL
authors.lastname: Jindrich
authors.forename: Aruna D
authors.initials: AD
authors.lastname: Balakrishnan
authors.forename: Jack T
authors.initials: JT
authors.lastname: Dennerlein
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000379:methods; D016287:Computer Peripherals; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D005384:Finger Joint / Q000502:physiology*; D005385:Fingers / Q000502:physiology*; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D013314:Stress, Mechanical; D019415:Torque; D014584:User-Computer Interface