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After nearly three decades in law enforcement, Jeffry Johnson still remembers vividly a "hellacious" physical fight for his life as a young cop.

"I was called to a scene where a guy was banging on his girlfriend's door, trying to break in," he told Force Science News recently. "He was BIG...and on PCP. Six of us wrestled with him, trying to get his arms behind his back for cuffing.

"He thrashed around like a fire hose out of control. He got an arm free and grabbed my gun. I fought with everything I had to keep it in my holster.

"Then suddenly I was juice left. It was shocking how fast I lost strength. If other officers hadn't been there and overpowered him, I honestly believe I would have died."

Johnson, now training commander for the Long Beach (Calif.) PD, had reached what he calls "the fatigue threshold" and runners know as "hitting the wall," a little-researched phenomenon with profound implications for use-of-force decisions and courtroom testimony. Spurred in part by lingering memories of his own desperate experience, Johnson has explored the causes and consequences of the condition in a recent article for the Monthly Law Journal, published online by Americans for Effective Law Enforcement, the legal information and training organization.

"Cop's worst nightmare"

In engineering, the fatigue threshold is the stress level at which steel or wood cracks, bends, or breaks. In law enforcement, Johnson explains, the term can be defined as "the sudden physical exhaustion experienced during a force encounter when an officer cannot effectively perform to either control a suspect or defend himself." It is "not the same as just being tired"; instead, it's the abrupt and utter depletion of energy "to the point that you cannot physically function."

For some officers, that dire moment can strike "in extreme cases" after as little as 30 seconds of maximum physical exertion, Johnson says. Others might last up to five minutes. On the whole, he estimates "an officer will be lucky if he or she has two to three minutes of effective strength in an all-out fight."

Reaching that threshold "is a cop's worst nightmare," Johnson declares. "The closer an officer gets to his or her personal fatigue threshold, the more dangerous the situation becomes, not only to the officer, but often to the suspect as well. You'll do anything to avoid it, including using what may otherwise be considered excessive force."

Physiological root

Physiologically, the fatigue phenomenon hinges on the difference between aerobic and anaerobic exercise. Aerobic exertion, like jogging and biking, can be sustained for long periods of time, Johnson explains, because the body "is able to keep a steady flow of oxygen and fuel to the muscles." But anaerobic exercise, such as strength/weight training and sprinting, is critically different.

While aerobic exercise primarily uses "slow twitch" muscles designed for endurance, anaerobic effort involves "fast twitch" muscles. "These are capable of faster, more explosive motion," but they burn much more energy and are "insatiable" for fuel, Johnson explains.

Fast-twitch muscles are those you depend on in a fight for explosive motion (swinging a baton, blocking, punching, kicking, grasping, clutching, etc.) and for forceful contraction or tension (prying arms out from under a suspect, keeping him from grabbing your or his weapons, holding him down, etc.).

In such anaerobic activity, these muscles "are contracting so quickly and/or powerfully that oxygen the body is taking in cannot provide enough fuel to sustain" them for a long duration. The body tries to compensate by drawing on sugar (glycogen), but that process is not sufficient long-term. The result: a waste product (lactic acid) builds up faster than the body can expel it.

"If the body is unable either to keep the muscles fed (through respiration and blood flow) and/or remove the lactic acid," Johnson writes, muscles at some point "simply stop contracting – shut down." At this threshold, they "are literally starved and suffocated...non-responsive."

A civilian witness may not realize how much exertion an officer is expending. "It takes a tremendous amount of strength to force a person's hands into handcuffing position if the subject doesn't want to go there," Johnson writes. "A suspect can easily lock his or her arms together against or under his body.... Even a suspect who is passively resisting....can easily bring an officer to his or her fatigue threshold."

Proper training – "intense, often bone jarring, high impact, task-specific training” – may extend your fighting ability somewhat, but it "doesn't eliminate the fatigue threshold – it just buys a little more time."


ref: The Forensic Science Research Center