Final Findings From Force Science Exhaustion Study

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The Force Science research team that explored officer exhaustion through a unique set of experiments in Canada last September has now issued its official findings—first presented in detail in the Force Science Certification Course conducted in Wisconsin this past week (4/18-4/22) and scheduled for integration into future courses—with these significant conclusions:

  • Less than 60 seconds of all-out exertion, such as an officer might expend in trying to control a combative offender, can deplete the average LEO’s physical reserves and put his life in peril;
  • Environmental awareness and memory are also affected adversely, hampering an involved officer’s ability to deliver accurate, detailed statements and testimony once a desperate fight is over;
  • Even officers in top condition are not immune to the rapid drain of physical prowess and cognitive faculties resulting from sustained hand-to-hand combat.

“The bottom line,” says Dr. Bill Lewinski, executive director of the Force Science Institute who headed up the research team, “is this: If an officer can’t resolve a struggle very quickly, a tactical withdrawal or swift escalation to a higher level of force may be necessary and justified for personal survival. And investigators and courts need to understand that an officer who doesn’t provide details surrounding a major physical conflict is not necessarily being deceptive, malicious, or uncooperative.”

TEST DESIGN

Force Science News explained the testing sequence of this research in Transmission #159 [9/24/10] soon after the project launched. To recap:

Researchers recruited 52 officer volunteers (42 males, 10 females), ranging in age from 23 to 51, with an average of 8 years on the job. All were “familiar with officer safety training involving high aerobic physical engagement,” according to Dave Blocksidge, a Force Science Analyst from the London (England) Metropolitan Police, and one of the research team.

“During an initial briefing, all the subjects were told to remain alert and try to absorb and remember as much as they could about what took place,” Lewinski says.

First they were given a crime report to read, which included details about the m.o. and descriptions of an armed robbery crew that had attacked 3 locations. Then in a gym used for training by the Winnipeg (Manitoba) Police Service, the officers were paired, with one-half instructed one at a time to launch a full-force physical attack on a 300-lb. hanging water bag and the others (a control group) assigned as “partners” to observe as the action took place. All were fitted with heart-rate monitors and the “physical exerters” also donned VO2 masks to measure oxygen consumption and gas exchange.

The exerters were told to attack the bag with as much ferocity as they could muster, selecting their own “assault movements”—punches, kicks, and/or palm, elbow, and knee strikes. During the attack, a researcher shouted “encouragement” (“Harder! Faster!”) on 3 occasions. Once the name of a familiar intersection in Winnipeg was yelled out and another time a random 3-digit number was hollered. Unknown to the participants, all this would prove relevant later in a memory test.

The exerters were to sustain assailing the bag until they no longer had strength to keep going or until they were visibly maxed out (“breathless and struggling to continue”) and were told to stop by exercise physiologist Justin Dixon of the London Police, who supervised this part of the experiment.

“In terms of upper-body involvement and energy expended, the bag drill realistically replicated a full-force fight by a moderately trained officer to control a strong, dynamically resisting suspect,” Lewinski explains. “Two officers actually collapsed, and the rest were severely taxed as they moved on to the next phase of the test.”

That required the exerter to run upstairs and outside to a trailer that a “known felon” was suspected of occupying, a distance of 145 feet. En route, the officer passed a gaudily dressed role-player holding an electric drill, who stared at the exerter intently but said nothing and made no aggressive moves.

Inside the trailer, the officer found a “living room” mocked up with furniture and a variety of visible weapons, including an M16 carbine, a revolver, a sawed-off shotgun, and a large kitchen knife. After a 5-second delay, a “critical target” emerged from another room—“a large, black, middle-aged male,” wearing a black t-shirt, blue jeans, and a black bandana. He screamed profanities at the officer, commanding him/her to get out. He was not armed, although several of the weapons were within his easy reach.

The trailer scenario lasted about 15 seconds. After that, the exerter was permitted some “recovery time” while his observer partner ran through the same trailer exercise.

After 3 minutes’ rest, Dixon drew a blood sample from each participant to measure lactic acid levels. The officers were also given informational “updates” about the robbery crew.

Then all completed a battery of memory tests administered by Dr. Lorraine Hope, a cognitive psychologist from England’s University of Portsmouth. This testing included a review of what exerters and observers could remember about what had happened and a photo lineup in which the officers were asked to pick out the suspect they’d confronted in the trailer.

PHYSICAL DECLINE

The heart monitors, face masks, and blood tests all confirmed that exerters reached an intense level of energy output during the bag blitz. Heart rates, for example, leaped from an average resting rate of 73 bpm to an average maximum of 179 for the bag beaters, significantly higher than the modest average rise to 104 bpm for the observers. The exerters’ blood lactate levels, reflecting the amount of exertion and affecting muscle function, skyrocketed up to 13 times the normal resting concentration. “It was impressive how committed these officers were to going flat out,” Lewinski remarks.

Most dramatic—and alarming—was the speed at which exerters depleted their physical resources. On average, the officers spent 56 seconds hitting the bag, although some either quit or were called out as thoroughly exhausted after as little as 25 seconds. The blows they were able to deliver ranged from a low of 73 to a high of 274. The average was 183. The overwhelming majority of hits were fist punches.

Reviewing time-coded video of the action, researchers were able to count second by second the number of times each participant struck the bag. The average officer peaked at 15 seconds. After that, the frequency of strikes fell in a sharp and steady decline.

“The officers started out strong, driving hard with penetrating hits that visibly moved the heavy bag,” Lewinski reports. “But by 30 to 40 seconds, most were significantly weakened. They were not able to breathe properly, their cadence dropped, their strikes scarcely moved the bag if at all, and they were resorting largely to very weak, slowly paced blows that would have had little impact on a combative assailant.”

In effect, Blocksidge states in a paper he has written about the research, the exerters “delivering a concerted and sustained physical assault…‘punched themselves out’ ” in a matter of seconds.

Perhaps surprisingly, this seemed true even of officers with a high level of personal fitness and fighting skill. Blocksidge offers this explanation: “Fitter officers delivered faster and more powerful strikes,” expending greater effort and thus exhausting their presumably greater reserves in “roughly the same time” as those less fit and skilled.

MEMORY DEFICIT

The officers’ exertion proved, for the most part, closely associated with incomplete and faulty memories of what they experienced. The exerters remembered “less visual and auditory information” and made “greater errors in recall” compared to the observing control group, Blocksidge reports.

Exerters and observers were asked to estimate within 90% the number of each type of blow delivered against the heavy bag. Exerters scored significantly better than observers in recalling the number of elbow, knee, and palm strikes they’d made. 89% of exerters, for example, estimated within the accepted accuracy range the number of elbow hits, compared to only 45% of observers.

“However, there were very few elbow, knee, and palm strikes made overall, so they tended to stand out in the exerters’ memory,” Lewinski explains. “But with the most common hits—punches—it was a far different story.” 25% fewer exerters than observers were able to estimate accurately the number of fist blows. “The more exhausted officers were, the less accurate their estimates tended to be,” notes researcher Hope.

Observers also were able to recall more by wide margins than exerters about the information that was shouted out during the bag blitz. Likewise, they were more accurate and more detailed in remembering information about the robbery crew.

As to the man with the drill who was encountered en route to the trailer, more than 90% of observers were able to recall at least one descriptive item about him, whereas nearly one-third of exerters did not remember seeing him at all.

Everyone remembered seeing the angry male in the trailer, but observers were able to correctly describe significantly more things about him, while making an average of half as many errors. And during the photo lineup, 54% of the observers correctly identified the suspect, compared to only 27% of the exerters. Typically, the tired officers expressed little certainty about the identifications they did make.

“As exhaustion takes over, cognitive resources tend to diminish,” Lewinski explains. “The ability to fully shift attention is inhibited, so even some potentially relevant information tends to get screened out. Ultimately, memory is determined by where the focus of attention was during an event. The exerters were zeroed in on delivering blows during the bag blitz. Afterward, they typically had little cognitive resources left.”

During the trailer encounter, however, the exerters were able to register threat cues. Here, in fact, their responses were virtually identical to those of observers. Six observers and 5 exerters remembered seeing no weapons at all. The most weapons noticed were 2, recalled by 4 observers and 5 exerters. However, 16 officers in each category remembered seeing one weapon, usually the largest (the carbine). (After noticing one, the researchers speculate, most officers may simply have quit scanning for more, having confirmed a potential life threat.)

“Fear conditioning through training,” Blocksidge writes, apparently “enables simple processing” of threat and danger cues to continue on some level “despite the impact of exhaustion and anxiety.” The ability to respond effectively to such cues, however, would be gravely degraded in an exhausted state, Lewinski points out.

IMPLICATIONS

As Lorraine Hope notes, “The legal system puts a great deal of emphasis on witness accounts, particularly those of professional witnesses like police officers.” After a violent confrontation, Blocksidge states, “it is commonly believed” that officers are capable of recalling relevant particulars, “such as subject position, number of blows, time sequences, verbal comments, and the position of colleagues…. Policing is quite unique within the cognitive field, since officers are [expected] to operate in a dual-task mode of…taking action whilst remembering…information.”

The gap documented by the study between what exerters and observers were able to remember means that in real-world conflicts “substantial aspects of visual details may remain [unnoticed] by active or involved witnesses while being noticed and attended by passive witnesses,” Blocksidge writes.

“If investigators and force reviewers don’t understand the implications of this study,” Lewinski cautions, “an officer’s memory errors or omissions after an intense physical struggle may unjustly affect his or her credibility. We think we have a lot of attentional resources working for us at all times, but in reality we don’t.”

In addition to illuminating memory issues, Lewinski is hopeful that the research findings will underscore the importance of tactical pre-assessment in deciding whether to engage or temporarily back off from potential physical conflict. “Officers need to read situations better before getting physically involved, knowing they have a limited capacity for all-out exertion,” he says.

When a struggle does occur, he hopes the findings will help officers, trainers, investigators, and reviewers better appreciate the justification in desperate circumstances for escalating force in order to end a dangerous fight quickly. “The longer physical combat lasts,” he explains, “the more at risk an officer is to the dire consequences of exhaustion. Very quickly an officer can reach the point of not having the energy or the ability to physically overcome resistance. Even a few seconds may make a difference between getting a suspect under control or the officer ending up badly hurt or killed.”

Sgt. Jason Anderson of Winnipeg Police Service’s Safety Unit, who assisted with the experiments, expresses gratitude for the study. He says it provides “data we can bring to court from a scientific organization using scientific methods and give the court the ability to properly assess these situations fairly.”

Statistical details from the study, which was funded fully by the Force Science Institute, will be included in a report the research team is preparing for publication in a peer-reviewed professional journal.

Meanwhile, footage shot by a Canadian Discovery Channel film crew is available for viewing, if you want to see how the experiments were conducted.

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