The Fatigue Threshold…An Officer’s Worst Nightmare

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After nearly 3 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 spent…no 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 (CA) 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.

(To access Johnson’s article, “Force and the Fatigue Threshold: The Point of No Return,” free of charge, CLICK HERE or type this address into your browser: www.aele.org/law/2010-06MLJ501.html


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 5 minutes. On the whole, he estimates “an officer will be lucky if he or she has 2 to 3 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.”


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…. [E]ven 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.”


How long it takes to reach the fatigue threshold differs among individuals, Johnson says. But one scientific source he cites indicates that certain muscles can be affected after “approximately 30 seconds of maximum-intensity exercise.” While “roughly” 1 to 5 minutes might seem a likely “normal” range, “don’t figure on most people being able to hold out for more than 2 minutes or so,” Johnson advises. “You don’t have much time to get a suspect under control before you’re going to be in trouble.”

Important to note: the suspect may not tire as quickly as you do, Johnson explains, “because it’s a lot easier to resist than to overcome resistance.”

The exact point can be influenced not only by the officer’s fitness level but also by such factors as the intensity of the altercation, the number of suspects and officers involved, the suspect’s physical condition, environmental influences (heat, humidity, cold), the officer’s equipment (20-lb. belt, motion-restricting ballistic vest, heat-retaining wool uniform) and the combatants’ “will to overcome and survive,” Johnson says.

The shut-down is temporary, but recovery may take as long as a quarter-hour—“precious minutes an officer can’t spare in a fight,” Johnson notes.


Before experiencing a life-threatening loss of physical capacity, “it may be necessary for [an] officer to consider and employ greater levels of force than may otherwise appear objectively reasonable, up to and including deadly force,” Johnson writes. The need for escalation may be especially urgent “if the suspect has a history of violence, has threatened the officer, or possesses a weapon.”

Once an officer hits the wall, “all gains are lost, all advantages evaporate,” he points out. “The reasonable officer understands that any suspect who is willing to fight the police with such intensity that he can bring the officer to the limits of his strength is dangerous and cannot be allowed to…control the outcome.”

In most cases, Johnson says, you can tell when you are about to reach your physical limit, although you may still be surprised at how rapidly you can fade, especially where upper-body strength is concerned. When you sense you’re nearing your threshold, you “must act quickly and decisively to control the suspect,” he says.

“An exhausted officer who has reached the limits of his or her physical endurance, yet still has not taken a resisting suspect into custody, may often have no other option than that of deadly force,” he writes. “Sometimes the 4-pound pull of a trigger is the only force option a threatened, exhausted officer can physically perform.

“This will never look good on video, but appearances to the untrained eye should never dictate our standard of objective reasonableness. We carry the burden of having to explain why we took the action we did. If you explain well, people will usually accept it.”


Getting into a life-on-the-line fight is rare for most officers, Johnson believes, but offering near-exhaustion as a justification for significantly escalating force in circumstances where it is a factor would be more credible to juries and review boards if more were known about the phenomenon.

“No one has yet researched the fatigue threshold in a law enforcement context,” says Dr. Bill Lewinski, executive director of the Force Science Institute. “We don’t know how long it takes for fatigue to strike at various levels of intensity, what the best exercise regimens are for maximizing anaerobic stamina, what techniques officers can employ to best marshal their strength in a fight, and so on. Finding answers to these and other related unknowns would be an invaluable contribution.”

He and Johnson hope to collaborate on such research in the near future.

Meanwhile, Johnson writes, “experience tells us that just because a problem is not comprehensively documented does not mean it does not exist. Without question, [the fatigue threshold] exists. What we still need to more clearly establish is the scope of its impact.”

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