Keyswitch Orientation Can Reduce Finger Joint Torques During Tapping on a Computer Keyswitch

Abstract

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° such that when pressed it moved away from the user (similar to a positive-tilt keyboard), and tilted 30° 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.

Get full access to this article

View all access options for this article.

References

Alexander, R. M. (1977). Mechanics and scaling of terrestrial locomotion. In T. J. Pedley (Ed.), Scale effects in animal locomotion (pp. 93–110). London: Academic.

Biewener, A. A. , & Full, R. J. (1992). Force platform and kinematic analysis. In A. A. Biewener (Ed.), Biomechanics: Structures and systems, a practical approach (pp. 75–96). Oxford, UK: IRL Press/Oxford University Press.

Bureau of Labor Statistics. (2002). Reports on survey of occupational injuries and illnesses in 1977--1997. Washington, DC: Author.

Craig, J. (1989). Introduction to robotics: Mechanics and control. Reading, MA: Addison-Wesley.

Faucett, J. , & Rempel, D. (1994). VDT-related musculoskeletal symptoms: Interactions between work posture and psychosocial work factors. American Journal of Industrial Medicine, 26, 597–612.

Feuerstein, M. , Armstrong, T. , Hickey, P. , & Lincoln, A. (1997). Computer keyboard force and upper extremity symptoms. Journal of Occupational and Environmental Medicine, 39, 1144–1153.

Gerard, M. J. , Armstrong, T. J. , Foulke, J. A. , & Martin, B. J. (1996). The effects of key stiffness on force and the development of fatigue while typing. American Industrial Hygiene Association Journal, 57, 849–854.

Gerard, M. J. , Armstrong, T. J. , Franzblau, A. , Martin, B. J. , & Rempel, D. M. (1999). The effects of keyswitch stiffness on typing force, finger electromyography, and subjective discomfort. American Industrial Hygiene Association Journal, 60, 762–769.

Gerr, F. , Marcus, M. , Ensor, C. , Kleinbaum, D. , Cohen, S. , Edwards, A. , et al. (2002). A prospective study of computer users: I. Study design and incidence of musculoskeletal symptoms and disorders. American Journal of Industrial Medicine, 41, 221–235.

10.

Hales, T. R. , Sauter, S. L. , Peterson, M. R. , Fine, L. J. , Putz-Anderson, V. , Schleifer, L. R. , et al. (1994). Musculosksletal disorders among visual display terminal users in a telecommunications company. Ergonomics, 37, 1603–1621.

11.

Harding, D. C. , Brandt, K. D. , & Hilberry, B. M. (1989). Minimization of finger joint forces and tendon tensions in pianists. Medical Problems of Performing Artists, 4, 103–108.

12.

Harding, D. C. , Brandt, K. D. , & Hillberry, B. M. (1993). Finger joint force minimization in pianists using optimization techniques. Journal of Biomechanics, 26, 1403–1412.

13.

Jindrich, D. L. , Balakrishnan, A. B. , & Dennerlein, J. T. (2004a). Effects of keyswitch design and finger posture on finger impedance during tapping on computer keyswitches. Journal of Clinical Biomechanics, 19, 600–608.

14.

Jindrich, D. L. , Balakrishnan, A. B. , & Dennerlein, J. T. (2004b). Finger joint impedance during tapping on a computer keyswitch. Journal of Biomechanics, 37, 1589–1596.

15.

Keir, P. J. , Wells, R. P. (2002). The effect of typing posture on wrist extensor muscle loading. Human Factors, 44, 392–403.

16.

Landsmeer, J. M. , & Long, C. (1965). The mechanism of finger control, based on electromyograms and location analysis. Acta Anatomica (Basel), 60, 330–347.

17.

Marklin, R. W. , Simoneau, G. G. , & Monroe, J. F. (1999). Wrist and forearm posture from typing on split and vertically inclined computer keyboards. Human Factors, 41, 559–569.

18.

Martin, B. J. , Armstrong, T. J. , Foulke, J. A. , Natarajan, S. , Klinenberg, E. , Serena, E. , et al. (1996). Keyboard reaction force and finger flexor electromyograms during computer keyboard work. Human Factors, 38, 654–664.

19.

Pascarelli, E. F. , & Kella, J. J. (1993). Soft-tissue injuries related to use of the computer keyboard: A clinical study of 53 severely injured persons. Journal of Occupational Medicine, 35, 522–532.

20.

Radwin, R. J. , & Jeng, O. J. (1997). Activation force and travel effects on overexertion in repetitive key tapping. Human Factors, 39, 130–140.

21.

Rempel, D. , Dennerlein, J. , Mote, C. D. Jr. , & Armstrong, T. (1994). A method of measuring fingertip loading during keyboard use. Journal of Biomechanics, 27, 1101–1104.

22.

Rempel, D. , Tittiranonda, P. , Burastero, S. , Hudes, M. , & So, Y. (1999). Effect of keyboard keyswitch design on hand pain. Journal of Occupational and Environmental Medicine, 41, 111–119.

23.

Serina, E. R. , Tal, R. , & Rempel, D. (1999). Wrist and forearm postures of users of conventional computer keyboards. Ergonomics, 42, 938–951.

24.

Tittiranonda, P. , Burastero, S. , & Rempel, D. (1999). Risk factors for musculoskeletal disorders among computer users. Occupational Medicine, 14, 17–38.

25.

Valero-Cuevas, F. J. (2000). Predictive modulation of muscle coordination pattern magnitude scales fingertip force magnitude over the voluntary range. Journal of Neurophysiology, 83, 1469–1479.

26.

Valero-Cuevas, F. J. , Zajac, F. E. , & Burgar, C. G. (1998). Large index fingertip forces are produced by subject-independent patterns of muscle excitation. Journal of Biomechanics, 31, 693–703.

27.

Weis, N. D. , Gordon, L. , Bloom, T. , So, Y. , & Rempel, D. M. (1995). Position of wrist associated with the lowest carpal-tunnel pressure: Implications for splint design. Journal of Bone and Joint Surgery [Am], 77, 1696–1699.