Objectives: To investigate whether unintended muscle activity induced by motor overflow can result in the unintentional discharge of a firearm. Background: In the past few years an increasing number of people have been injured, sometimes fatally, as a result of police weapons being discharged involuntarily. Methods: Two experiments were performed using a pistol fitted with sensors to register the pressure exerted on the hand stock and the trigger. In Study 1, 34 police officers reacted to a set case using the prepared pistol. In Study 2, 25 participants performed 13 tasks requiring the use of different limbs. Results: In Study 1, about 20% of participating officers made contact with the trigger, thus violating police regulations to keep the trigger finger outside the trigger guard at all times until a conscious decision to fire has been made. Study 2 showed that motor activity in different limbs leads to a significant increase in grip force exerted on a firearm (significant results for 12 of 13 trials, Bonferroni-corrected p < .004). Furthermore, pressure on the trigger resulting from involuntary muscle contractions was, in certain cases, sufficient to unintentionally discharge a weapon. Conclusion: Unintentional discharges attributable to involuntary muscle activity can be a real danger for police officers when carrying out their duties. Application: Results may help improve police training with the aim of reducing the danger of involuntary discharges in real-life situations.
Get full access to this article
View all access options for this article.
References
1.
Arányi, Z., & Rösler, K. M. (2002). Effort-induced mirror movements. Experimental Brain Research, 145, 76–82.
2.
Archontides, C., & Fazey, J. A. (1993). Inter-limb interactions and constraints in the expression of maximum force: A review, some implications and suggested underlying mechanisms. Journal of Sports Sciences, 11, 145–158.
3.
Armatas, C. A., Summers, J. J., & Bradshaw, J. L. (1994). Mirror movements in normal adult subjects. Journal of Clinical and Experimental Neuropsychology, 16, 405–413.
4.
Aveni, T. J. (1995). The trigger finger dilemma: A perspective revisited. Retrieved June 2, 2006, from http://www.smith-wesson.com/webapp/wcs/stores/servlet/CustomContentDisplay?storeId=10001&catalogId=10001&content=22313§ionId=10503.
5.
Bemben, M., Clasey, J., & Massey, B. (1990). The effect of the rate of muscle contraction on the force-time curve parameters of male and female subjects. Research Quarterly for Exercise and Sport, 61, 96–99.
6.
Corna, S., Galante, M., Grasso, M., Nardone, A., & Schieppati, M. (1996). Unilateral displacement of lower limb evokes bilateral EMG responses in leg and foot muscles in standing humans. Experimental Brain Research, 109, 83–91.
7.
Delwaide, P. J., & Toulouse, P. (1983). The Jendrassik maneuver: Quantitative analysis of reflex reinforcement by remote voluntary muscle contraction. In J. E. Desmedt (Ed.), Motor control mechanisms in health and disease (pp. 661–669). New York: Raven Press.
8.
Duchateau, J., & Enoka, R. M. (2002). Neural adaptations with chronic activity patterns in able-bodied humans. American Journal of Physical Medicine and Rehabilitation, 81 (Suppl. 11), S17–S27.
9.
Engelbrecht, H. O., & Buhr, J. (2003). Schießausbildung [Firearms training]. Stuttgart, Germany: Boorberg Verlag.
10.
Enoka, R. M. (1991, September). Involuntary muscular contraction and accidental discharge of a firearm. Presented at the Annual Training Conference of the International Association of Law Enforcement Firearms Instructors (IALEFI) meeting in Mesa, Arizona on September 25, 1991.
11.
Enoka, R. M. (2003). Involuntary muscle contractions and the unintentional discharge of a firearm. Law Enforcement Executive Forum, 3(2), 27–39.
12.
Grossi, D. (1993). Unintentional discharges: A training concern. The Police Marksman, 2, 23–26.
13.
Janssen, W., Kulle K. J., Gehl, A., & Püschel, K. (2001). Der ungewollte Schuss im Polizeieinsatz [Involuntary discharges during police operations]. Archiv für Kriminologie, 207, 1–11.
14.
Kearney, R. E., & Chan, C. W. Y. (1981). Interlimb reflexes evoked in human arm muscles by ankle displacement. Electroencephalography and Clinical Neurophysiology, 52, 65–71.
15.
Lee, C., & Nolte, K.B. (2001). Two separate unintentional fatalities with the same revolver. Annals of Emergency Medicine, 37, 333–336.
16.
Leen, J., & Horwitz, S. (1998, November 18). Armed and unready. Washington Post, p. A1
17.
Li, Z. M., Latash, M. L., Newell, K. M., & Zatsiorsky, V. M. (1998). Motor redundancy during maximal voluntary contraction in four-finger tasks. Experimental Brain Research, 122, 71–78.
18.
Moore, J. C. (1975). Excitation overflow: An electromyographic investigation. Archives of Physical Medicine and Rehabilitation, 56, 115–120.
19.
Niebergall, E. (1998). Wenn der Körper fatal reagiert [When the body reacts fatally]. Polizei-heute, 3, 98–101.
20.
Noteboom, J. T., Barnholt, K. R., & Enoka, R. M. (2001). Activation of the arousal response and impairment of performance increase with anxiety and stressor intensity. Journal of Applied Physiology, 91, 2093–2101.
21.
O'Brien, J. (2002). Experts find Glocks prone to accidents. Retrieved May 31, 2006, from http://www.cominolli.com/postnews2.pdf.
22.
Sherrington, C. S. (1906). The integrative action of the nervous system. New Haven, CT: Yale University Press.
23.
Shinohara, M., Keenan, K.G., & Enoka, R. M. (2003). Contralateral activity in a homologous hand muscle during voluntary contractions is greater in old adults. Journal of Applied Physiology, 94, 966–974.
24.
Sinauer, N., Annest, J.L., & Mercy, J. A. (1996). Unintentional, nonfatal firearm-related injuries: A preventable public health burden. Journal of the American Medical Association, 275, 1740–1743.
25.
Talsania, J. S., & Kozin, S. H. (1998). Normal digital contribution to grip strength assessed by a computerized digital dynamometer. Journal of Hand Surgery, 23, 162–166.
26.
Traub, M. M., Rothwell, J. C., & Marsden, M. C. D. (1980). Anticipatory postural reflexes in Parkinson's desease and other akinetic-rigid syndromes and in cerebellar ataxia. Brain, 103, 393–412.
27.
Tully, E. (1996). Unintentional discharge of police weapons (Part 1). Blue Line Magazine, 8(10), 18–21.
28.
Tully, E. (1997). Unintentional discharge of police weapons (Part 2). Blue Line Magazine, 9(1), 9–11.
29.
Weinberg, R. S., & Hunt, V. V. (1976). The interrelationships between anxiety, motor performance, and electromyography. Journal of Motor Behavior, 8, 219–224.
30.
Yensen, R. (1965). A factor influencing motor overflow. Perceptual and Motor Skills, 20, 967–968.
31.
Zijdewind, I., & Kernell, D. (2001). Bilateral interactions during contractions of intrinsic hand muscles. Journal of Neurophysiology, 85, 1907–1913.
