Police officers who engage in at least 60 seconds of intense physical energy while involved in a combative encounter may suffer memory loss, according to a newly published study in the journal Psychological Science.

Researchers found that officers chasing down a suspect or engaging in a physical altercation with someone can often forget details of the incident, including being unable to identify the suspect from a lineup.

The study's lead author, Dr. Lorraine Hope, University of Portsmouth, United Kingdom, said the study's findings are a "warning" to officers, police chiefs and even the court system.

"Police officers are often expected to remember in detail who said what and how many blows were received in the midst of physical struggle or shortly afterwards," said Hope. "The results of our tests indicate it may be very difficult for them to do this."

The study followed 52 police officers - 42 men and 10 women - in Winnipeg, Canada, who had been on the job about 8 years. All exercised regularly and were considered fit and healthy.

The officers were split into two groups; both groups attended a briefing and got information on three armed robberies. They viewed a six-person lineup of color pictures. The group was split into pairs where one officer rigorously assaulted a punching bag until he was visibly tired, the other did not. They were then taken to a trailer set up to represent a realistic "home" environment complete with a "target" individual who had access to multiple weapons strategically placed around the room.

Each officer went through a scenario where there was a brief but angry verbal confrontation with that person. Shortly after the scenario was over, officers were given three memory tests. They were asked to recall details of their initial briefing, the encounter - and then shown the lineup photographs.

Researchers found the group that physically exerted themselves remembered less information from the original briefing and the encounter with the target individual. In fact, more than 90% of the officers in the non-exertion group could recall at least one detail about the target. Barely a third of the officers who were involved in the physical activity remembered seeing the target person at all.

"As exhaustion takes over, cognitive resources tend to diminish." Hope said. "The ability to fully shift attention is inhibited, so even potentially relevant information might not be attended to. Ultimately, memory is determined by what we can process and attend to."

Sgt. Jason Anderson, a use of force instructor with the Winnipeg Police Service said the research will help training officers learn more about what can happen under adverse conditions.

"It will allow officers to understand that they are not 'wrong.' 'lying.' or lacking 'what it takes' because they cannot remember certain aspects of a volatile, life threatening hand-to-hand physical combat encounter," said Anderson.

The study, he said, reinforces the idea that it's OK to say, "I don't remember" or "I can't recall."

"That is simply reality," said Anderson. "I don't care how good of shape you're in, when you reach your personal physical breaking point or extreme exhaustion, your sole focus is on remaining conscious and alive. Your memory will be adversely and dramatically effected during a combat encounter."

All the study participants remembered seeing the angry suspect in the trailer. But the non-exerted officers provided a "significantly more detailed description" of him and made half as many errors in recall as those who were exhausted, the study said.

"These observers were also twice as likely to correctly identify the suspect from a line-up," according to the research. There was no difference in how the officers registered threat cues.

The study is the first of its kind to test eyewitness recall after physical exertion, researchers said. Anderson believes it will have far-reaching implications for law enforcement and court cases.

"Law enforcement can now back up our subjective beliefs and observations for the first time using science to support us," Anderson said. "It is OK to say, 'No, I do not recall the color of his hat,' 'No, I can't remember what he or that bystander said,' 'No, I don't recall how many punches, knee strikes, elbows, etc., that I delivered or exactly where I delivered them."

Anderson said that ultimately, "under extreme exhaustion and attack, officers are trying to go home. They are trying to stay alive. People need to be educated on the realities of these encounters. This study is an extremely important tool in this education."

The Winnipeg Police Department has not made any changes based on the study results, but uses the findings when training recruits.