Oscar Pistorius's tie is adjusted by his uncle Arnold during his trial in the North Gauteng High Court in Pretoria on Thursday. Picture: Herman Verwey

Pretoria - Oscar Pistorius has an increased response to dangerous or stressful situations because of his disability, his life experience and training as an athlete.

This was according to an expert testimony at the athlete's murder trial.

Pistorius has been charged with the murder of his girlfriend, Reeva Steenkamp, but the athlete claims he shot at her through a closed door because he was convinced she was an intruder breaking into his home.

Returning to the stand on Thursday morning was sports scientist Professor Wayne Derman.

On Wednesday, Derman said he had worked with Pistorius for six years, and even used him as a subject in his research that showed disabled athletes were more prone to experience psychological distress than their able-bodied counterparts, especially after competitions.

Testifying in the North Gauteng High Court in Pretoria, Derman said that his analysis of Pistorius showed the athlete was even more prone to distress than most of the other people participating in the study.

The expert also indicated to the court that the fight or flight response of a disabled person is significantly more pronounced than that of an able-bodied person.

He also provided a research report by the World Health Organisation that showed that disabled people were more likely to be targeted by violent attacks because of their vulnerability.

The doctor also said that in his personal interactions with the Blade Runner, he noted that Pistorius was “hypervigilant” with a hand tremor, had a sleeping disorder and would cower when experiencing loud noises.

On Thursday morning, Derman continued with his analysis of the fight or flight response, and Pistorius's own reaction the night he shot and killed Steenkamp.

According to Derman, the body can experience several primal reactions in fear situations, from freezing to fleeing or pumping adrenaline to confront the threat.

Defence advocate Kenny Oldwadge asked about Pistorius's behaviour and what the athlete had told the court during his cross-examination.

Pistorius said he had felt vulnerable when he thought an intruder had entered his home, but chose to confront the danger anyway.

Derman said in his expert opinion, this would be normal behaviour, consistent with the reflexes of fight or flight. He said that when this response kicks in, there is less typical thinking going on in a person's mind and instincts take over.

He said if the mind had completely disregarded the thought of fleeing from the danger, the only other response is to fight.

Derman added that someone with limited mobility like Pistorius, a double-amputee, would be unable to flee.

Pistorius claimed that he heard two noises coming from the bathroom the night of the shooting. Derman said these auditory stimuli activated Pistorius's fight or flight response, first causing the athlete to freeze before choosing to confront the perceived danger.

Derman said he had often been questioned about how he could consider Pistorius as “disabled” considering his extreme speed and mobility when using his prosthetics.

But the doctor said that even he does not fully understand the psychology of disabled people.

He said that while Pistorius is a successful athlete, he is still an individual with a severe disability and without prosthetics is only 1.5m-tall.

Even though he appears to have triumphed over his disability, he would often still have insecurities about himself because of it.

Derman said he constructed a survey among his patients asking how deeply their lives were affected by their disability.

Many said that it affected their self-esteem, personal lives, working ability, leisure time and travelling. He said disabled people often experienced exclusion from social activities, and are treated differently by the able-bodied. He said even basic daily tasks are far more difficult for physically disabled people.

He said that for someone with prosthetic legs, reacting to anything took time, with feelings of vulnerability about personal safety and the protection of significant others.

In his report, Derman said Pistorius had an exaggerated “startle response”, is hypervigilant and is insecure because of his disability and some of the hardships he faced earlier in his life.

Derman said that Pistorius's startle response was evident in the testimony of other witnesses in the case, including his ex-girlfriend Samantha Taylor. He had reacted rashly after hearing a noise in the middle of the night. In another incident at a friend's home, he had run from the room after falling asleep during a movie and was startled awake by gunshots in the film.

Derman said that Pistorius's vulnerability exacerbated his fear of crime that had been present since childhood.

The expert said that Pistorius, as an athlete, had been trained to physically respond to sound, such as the shot indicating the start of a race.

Oldwadge referred to a psychologist's report commissioned by the state that said Pistorius had no general anxiety disorder that affected his behaviour on the night of the shooting.

But Derman said Pistorius fell just short of the cut-off, narrowly missing such a diagnosis.

It also stated that Pistorius has a fear of being trapped without his prosthetics, as well as anxiety in public spaces.

Derman's own report also referred to the “two Oscars”, the vulnerable, short, disabled person; and the tall, fearless global athlete.

This split in his persona caused further psychological distress.

He then provided his full analysis of the night of the shooting.

Derman said that Pistorius's enhanced fight or flight response, and inability to flee because of his limited mobility, ultimately resulted in the tragic death of Reeva Steenkamp.

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The Star