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The human sympathetic nervous system (SNS) releases adrenaline into the body during elevated states of arousal (stress). This “fight or flight” response

prepares the body to address a perceived threat, and can begin before the brain fully recognizes the threat’s potential. Some simultaneous preparations include an accelerated heart rate and increased blood pressure, sweating, “goose bumps,” and the dilation of the pupils. Some individuals have learned to function with high levels of adrenaline.

“. . . the sympathetic nervous system will control and dominate all motor action when [an officer] is confronted with a spontaneous deadly force threat (Siddle, 1995).”

Executive motor programs include those learned skills and systems law enforcement officers may learn in their pre-service academies and agencies. However, those skill sets may be initially over-ridden when the SNS is sufficiently activated.

Law enforcement and military trainer, Tony Blauer, was one of the first instructors to examine SNS responses as they relate to the startle reaction and self defense. Blauer found that startle reaction is initiated when the brain perceives a potential threat that presents itself too quickly to be processed cognitively. The brain recognizes the proximity and aggressiveness of the threat, and the suddenness of the attack, and the startle reaction then produces a flinch in response, which over-rides any trained motor programs and typically involves the head ducking, and the hands raising or pushing the perceived danger away. Blauer noted that the speed of these involuntary flinches may correspond to the type of startle stimulus, describing them from slowest to fastest, as visual, auditory, and tactile.

Blauer’s research and training appear to be supported by unassociated studies and researchers/instructors (Westmoreland Weaver stance study, Force Science Institute, multiple other instructors and disciplines), and a careful examination of recorded encounters involving a startle reaction.


Can a law enforcement officer’s training over-ride a sympathetic nervous system (SNS) reaction? Why, or why not?

Can a law enforcement officer’s training influence a sympathetic nervous system (SNS) reaction? Why, or why not? If so, what would be required?

Should a law enforcement officer’s SNS reaction be considered when objectively analyzing a use of force for reasonableness? Why, or why not? If so, how?

Does an understanding of SNS reactions have any relevance to civilian uses of force?


Siddle, B. (1995). Sharpening the Warrior’s Edge. PPCT Research Publications, Bellville, IL

Westmoreland, H. (1989). Isosceles VS. Weaver Shooting Stances. Law and Order Volume:37 Issue:10 Dated:(October) Pages:55-64.

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