The purpose of this study was to determine the differences in the electromyographic (EMG) activity of the posterior musculature of the trunk while subjects were first seated on a conventional chair, and then while the chair surface was inclined anteriorly to 100 and 110 deg. Twenty healthy subjects had electrodes applied lateral to the spinous processes of C6, T10, and L3 while EMG was monitored every other minute for 15 minutes. All subjects assumed each posture and used a keyboard to operate an interactive computer terminal. Before analysis, all data were processed by root-mean-square circuit and normalized to the EMG from maximum voluntary contractions. Analyses of variance showed significant differences (p < 0.0005) between postures; the EMG activity was found to be less with greater inclination of the chair seat.
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References
1.
Andersson, B. J. G., Ortengren, R., Nachemson, A., and Elfstrom G. (1974). Lumbar disc pressure and myoelectric back muscle activity during sitting. I. Studies on an experimental chair. Scandinavian Journal of Rehabilitation Medicine, 6, 104–114.
2.
Andersson, B. J. G., Ortengren R., Nachemson, A., and Elfstrom G. (1974). Lumbar disc pressure and myoelectric back muscle activity during sitting. IV: Studies on a car driver's seat. Scandinavian Journal of Rehabilitation Medicine, 6, 128–133.
3.
Andersson, B. J. G., Ortengren, R., Nachemson, A. L.Elfstrom, G., and Broman, H. (1975). The sitting posture: An electromyographic and discometric study. Orthopedic Clinics of North America, 6, 105–120.
4.
Barkla, D. M. (1964). Chair angles, duration of sitting and comfort ratings. Ergonomics, 7, 297–304.
5.
Bendix T., and Biering-Sorenson, F. (1983). Posture of the trunk when sitting on forward inclining seats. Scandinavian Journal of Rehabilitation Medicine, 15, 197–203.
6.
Brunswic, M. (1984). Seat design in unsupported sitting. In Proceedings of the 1984 International Conference on Occupational Ergonomics (pp. 294–298). Rexdale, ON: Human Factors Association of Canada.
7.
Burandt, U. (1969). Röntgenuntersuchung über die Stellung von Becken und Wirbelsaule beim Sitzen auf vorgeneigten Flachen. (X-ray examination of the position of the pelvis and spine with sitting on a forwardly inclined surface). In E. Grandjean (Ed.), Sitting posture (pp. 242–250). London: Taylor and Francis.
8.
Burandt, U., and Grandjean, E. (1963). Sitting habits of office employees. Ergonomics, 6, 217–228.
9.
Caldwell, L. S., Chaffin, D. B., Dukes-Dobos, R. N., Kromer, K. H. E., Laubach, L. L., Snook, S. H., and Waserman, D. E. (1974). A proposed standard procedure for static muscle strength testing. American Industrial Hygiene Association Journal, 35, 201–206.
10.
Drury, C. G., and Francher, M. (1985). Evaluation of a forward-sloping chair. Applied Ergonomics, 16, 41–47.
11.
Eastman, M. C., and Kamon, E. (1976). Posture and subjective evaluation at flat and slanted desks. Human Factors, 18, 15–26.
12.
Floyd, W. F., and Roberts, D. F. (1958). Anatomical and physiological principles in chair and table design. Ergonomics, 2, 1–16.
13.
Floyd, W. F., and Silver, P. H. S. (1955). The function of the erectore spinae muscles in certain movements and postures in man. Journal of Physiology, 129, 184–203.
14.
Fountain, F. P., Minear, W. L., and Allison, R. D. (1966). Function of longus colli and longissimus cervicis muscles in man. Archives of Physical Medicine, 47, 665–669.
15.
Keegan, J. J. (1953). Alterations to the lumbar curve related to posture and seating. Journal of Bone and Joint Surgery, 35 (Am), 567–589.
16.
Knutsson, B., Lindh, K., and Telhag H. (1966). Sitting---An electromyographic and mechanical study. Acta Orthopaedica Scandinavica, 37, 415–428.
17.
Kroemer, K. H. E. (1971). Seating in plant and office. America Industrial Hygiene Association Journal, 32, 633–652.
18.
Lueder, R. K. (1983). Seat comfort: A review of the construct in the office environment. Human Factors, 25, 701–711.
19.
Lundervold, A. (1951). Electromyographic investigations during sedentary work, especially typewriting. British Journal of Physical Medicine, n.s.14, 32–36.
20.
Mandal, A. C. (1981). The seated man (homo sedens): The seated work position. Theory and practice. Applied Ergonomics, 12, 19–26.
21.
McCormick, E. J., and Sanders, M. S. (1982). Human factors in engineering and design. New York: McGraw Hill.
22.
Okada, M. (1972). An electromyographic estimation of the relative muscular load in different human postures. Journal of Human Ergology, 1, 75–93.
23.
Schlegel, K. F. (1956). Sitzschaden und deren vermeidung durch eine neuartige sitzkonstruction. (Sitting injuries and their avoidance through a novel type of chair construction). Medizinische Klinik, 51, 1940–1942.
24.
Schneider, H. J., and Lippert, H. (1961). Das sitzproblem in funktionell-anatomischer sicht. (The sitting problem from a functional-anatomy view). Medizinsche Klinik, 56, 1164–1168.
25.
Soderberg, G. L., and Cook, T. M. (1984). Electromyography in biomechanics. Physical Therapy, 64, 1813–1820.
26.
Winter, D. A. (1979). Biomechanics of human movement. New York: Wiley.
