This study examines the relationship between forearm EMGs and keyboard reaction forces in 10 people during keyboard tasks performed at a comfortable speed. A linear fit of EMG force data for each person and finger was calculated during static fingertip loading. An average r2 of .71 was observed for forces below 50% of the maximal voluntary contraction (MVC). These regressions were used to characterize EMG data in force units during the typing task. Averaged peak reaction forces measured during typing ranged from 3.33 N (thumb) to 1.84 N (little finger), with an overall average of 2.54 N, which represents about 10% MVC and 5.4 times the key switch make force (0.47 N). Individual peak or mean finger forces obtained from EMG were greater (1.2 to 3.2 times) than force measurements; hence the range of r2 for EMG force was .10 to .46. A closer correspondence between EMG and peak force was obtained using EMG averaged across all fingers. For 5 of the participants the force computed from EMG was within ±20% of the reaction force. For the other 5 participants forces were overestimated. For 9 participants the difference between EMG estimated force and the reaction force was less than 13% MVC. It is suggested that the difference between EMG and finger force partly results from the amount of muscle load not captured by the measured applied force.
Get full access to this article
View all access options for this article.
References
1.
Alden, D. G., Daniels, R. W., & Kanarick, A. F. (1972). Keyboard design and operation: A review of the major issues. Human Factors,14, 275–293.
2.
Human Factors and Ergonomics Society. American national standard for human factors engineering of visual display terminal workstations (ANSI/HFS 100-1988). Santa Monica, CA: Author.
3.
Armstrong, T., Buckle, P., Fine, L., Hagberg, M., Jonsson, B., Kilbom, A., Kuorinka, I., Silverstein, B., Sjogaard, B., & Viikari-Juntura, E. (1993). A conceptual model for work-related neck and upper-limb musculoskeletal disorders. Scandinavian Journal of Work Environmental Health,19, 73–84.
4.
Armstrong, T. J., Foulke, J. A., Martin, B. J., Gerson, J., & Rempel, D. (1994). Investigation of applied forces in alphanumeric keyboard work. American Industrial Hygiene Association Journal,55, 30–35.
5.
Armstrong, T. J., Radwin, R. G., Hansen, D. J., & Kennedy, K. W. (1986). Repetitive trauma disorders: Job evaluation and design. Human Factors,28, 325–336.
6.
Basmajian, J. V., & De Luca, C. J. (1985). Muscle alive. (5th ed.) Baltimore, MD: Williams & Wilkins.
7.
Bureau of National Affairs. (1992). Repetitive stress suits across the nation.Occupational Safety and Health Reporter,22, 1186.
8.
Colombini, D., Occhipinti, E., Molteni, G., Semerano, D., & Grieco, A. (1989). A study of muscle activity in workplaces with keyboard operations. Milan: Ergodigit.
9.
Dickson, R. A., Petrie, A., Nicolle, F. V., & Calnan, J. S. (1972). A device for measuring the force of the digit of the hand. Biomedical Engineering,7, 270–273.
10.
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.
11.
Fernstrom, E., Ericson, M. O., & Malker, H. (1994). Electromyography activity during typewriter and keyboard use. Ergonomics,37, 477–484.
12.
Follows, A. M. (1986). Electromyographical analysis of the extrinsic muscles of the long finger during pinch activities. Occupational Therapy Journal of Research,7, 163–180.
13.
Galen, M., Mallory, M., Siwolop, S., & Garland, S. (1992, July 13). Repetitive stress: The pain has just begun. Business Week, 3274, 142–144.
14.
Guggenbühl, U., & Krueger, H. (1990). Musculoskeletal strain resulting from keyboard use. In L. Berlinguet & D. Berthelette, (Eds.), Proceedings of work with display units 89 (pp. 121–128). Amsterdam: North-Holland.
15.
Haaland, J., Wingert, J., & Olson, B. A. (1963, February 23). Force required to actuate switches, maximum pushing force, and coefficient of friction of mercury gloves (Honeywell Tech. Memorandum). Minneapolis, MN: Honeywell.
16.
Hill, A. V. (1938). The heat of shortening and the dynamic constants of muscles. Proceedings of the Royal Society, B126, 136–195.
17.
Ketchum, L. D., Thompson, D., Pocock, G., & Wallingford, D. (1978). A clinical study of forces generated by the intrinsic muscles of the index finger and the extrinsic flexor and extensor muscles of the hand.American Journal of Hand Surgery,3, 571–578.
18.
Landsmeer, J. M. F., & Long, C. (1965). The mechanism of finger control, based on electromyograms and location analysis. Acta Anatomica,60, 330–347.
19.
Laubach, L. L. (1976). Comparative muscular strength of men and women: A review of the literature. Aviation, Space and Environmental Medicine,47, 534–542.
20.
Lawrence, J. H., & De Luca, C. J. (1983). Myoelectric signal vs. force relationship in different human muscles. Journal of Applied Physiology,54, 1653–1659.
21.
Long, C., & Brown, M. E. (1962, September). Electromyographic kinesiology of the hand: Part M. Lumbricalis and flexor digitorum profundus to the long finger. Archives of Physical Medicine, 450–460.
22.
Lundervold, A. J. S. (1951). Electromyographic investigations of position and manner of working in typewriting.Acta Physiologica Scandinavica,24 (Suppl. 84).
23.
MacKay, D. G. (1982). The problem of flexibility. fluency and speed-accuracy trade-off in skilled behavior. Psychological Review,89, 483–506.
24.
Person, R. S., & Roshtchina, N. A. (1958). Electromyographic investigation of coordinated activity of antagonistic muscles in movements of the fingers of the human hand. Journal of Physiology (USSR),94, 455–462.
25.
Potosnack, K. M. (1988). Keys and keyboards. In M. Helander (Ed.), Handbook of human-computer interaction (pp. 475–494. Amsterdam: Elsevier.
26.
Rempel, D. M., Martin, B. J., Armstrong, T. J., Natarajan, S., Klinengerg, E., & Serina, E. (1994). Finger force during computer keyboard work: Part II. Relation of keyswitch make force to applied force and surface EMG. In Proceedings of the 12th Triennial Congress of the International Ergonomics Association (pp. 201–203). London: Taylor & Francis.
27.
Roebuck, J. A., Kroemer, K. H. E., & Thomson, W. G. (1975). Engineering anthropometry methods. New York: Wiley-Interscience.
28.
Semjen, A., & Gottsdanker, R. (1992). Plans and programs for short movement sequences. In G. Stelmach & J. Requin, (Eds.), Tutorials in motor behavior II (pp. 211–228. Amsterdam: Elsevier.
29.
Shaffer, L. H. (1976). Intention and performance. Psychological Review,83, 375–393.
30.
Shaffer, L. H. (1980). Analyzing piano performance: A study of concert pianists. In G. Stelmach & J. Requin, (Eds.), Tutorials in motor behavior I (pp. 443–455). Amsterdam: Elsevier.
31.
Shaffer, L. H. (1984). Motor programming in language production. In H. Bouma & D. Bouwhuis, (Eds.), Attention and performance X: Control of language processes (pp. 17–41. Hillsdale, NJ: Erlbaum.
32.
Sternberg, S., Monsell, S., Knoll, R. L., & Wright, C. E. (1978). The latency and duration of rapid movement sequences: Comparison of speech and typewriting. In G. Stelmach (Ed.), Information processing in motor control and learning (pp. 117–152). San Diego, CA: Academic,
33.
Swanson, A. B., Matev, I. B., & de Groot, G. (1970). The strength of the hand. Bulletin of Prosthetics Research, Fall, 145–153.
34.
Trombly, C. A., & Cole, J. M. (1979). Electromyographic study of four hand muscles during selected activities. American Journal of Occupational Therapy,33, 440–449.
