Pistorius: Fleeing not option

The final defence witness in the Oscar Pistorius trial has told a court why the athlete did not flee from his house on the night he shot dead his girlfriend.

The Paralympian and Olympian denies murdering 29-year-old model Reeva Steenkamp, claiming he shot her after mistaking her for an intruder at the Pretoria property.

On the 37th day of the trial, the defence read from Pistorius' evidence - the part where he was questioned about why he went towards danger.

Professor Wayne Derman, who worked with the South African Paralympic team, was asked to explain why the defendant would have headed in that direction after allegedly being startled by a noise.

The physician said it was consistent with the 'flight or fight' reflex and he said there was less ability to "think" after such a response kicked in.

Mr Derman said fleeing was not an option as the athlete has no lower legs - the other option was to fight and approach danger.

The defendant, who had fired his pistol through a closed toilet door in his home, was hyper-sensitive to sound and has a heightened fight or flight response, he also said.

South African Pistorius, 27, is vulnerable and his fear of crime is exacerbated by his physical disability, Mr Derman told the court.

His lower legs were amputated as a baby because he was born without fibula bones.

Mr Derman, a professor of sport and exercise medicine at the University of Cape Town, also described the athlete as a "paradox".

He said there were two Oscars - one winning races with his hands up and tall on his prosthetic legs - the other disabled on stumps.

"It is different each day," he said, adding the contrast causes stress and anxiety for the double-amputee runner.

The defence wants to show Pistorius' alleged sense of vulnerability was a factor in the night-time shooting on Valentine's Day last year.

Under cross-examination, the prosecution claimed Mr Derman could not give objective evidence as an "expert" as it might harm his patient.

But Mr Derman rejected this and said he had backed up his points with science.

On Wednesday, the court heard the defendant has been suffering from post-traumatic stress disorder (PTSD) since shooting her and needs to continue being treated to avoid the risk of suicide.

A psychiatric report found Pistorius is not mentally ill, but has been "severely traumatised" by the events of last year.

The athlete, who is on bail, faces 25 years to life in prison if found guilty of premeditated murder.

But he could also be sentenced to a shorter prison term if convicted of murder without premeditation or negligent killing.

The trial has been adjourned until Monday.