Daniel Roberts, 26, blamed his violent behaviour on taking steroids, crack cocaine, cocaine and booze. But the court heard he had previous convictions for assaulting a different woman in 2016.
Shrewsbury Crown Court heard that the latest case involved him injuring two girlfriends last year following minor arguments.
Mr Robert Edwards, prosecuting, said he held a lock knife to the throat of one of the victims before cutting her leg during an incident at her Shrewsbury home on May 2. The woman told police that he had strangled her to the point of unconsciousness.
Roberts also put her in a headlock before dragging her to the floor, spitting on her before twice punching her in the face resulting in black eyes.
After taking her to hospital he told her, "I only gave you seven out of 10. I could have done more damage".
The matter came to light after Roberts lashed out and swiped a glass which struck another customer while they were on a night out Shrewsbury's Bulls Head pub on May 10. The door staff ejected him and phoned the police.
When officers arrived the woman, who remained in the pub, told them about the incident at her home. They then split up.
While he was on bail Roberts, of Birch Close, in Ruyton-XI-Towns, struck up a new relationship.
Mr Edwards said in September the defendant and the second woman were staying in Wellington, and on two occasions he deliberately tripped her up following arguments causing her to fall. On the first occasion he beat her up in a "sustained" attack then apologised afterwards.
On the next occasion he struck her over her head, snatched her door key and used it to cut her neck causing it to bleed. The relationship ended days later after she broke down in tears at work.
Roberts at first denied all the allegations but pleaded guilty to wounding, assault occasioning actual bodily harm and affray ahead of the trial.
Mitigating, Mr Kevin Jones said Roberts wanted to tell his victims that he was "truly sorry" and had spent 435 days in custody since his last arrest. He said he was tackling his drug abuse and anger issues.
But Judge Anthony Lowe said the defendant's actions had a "sadistic element".
He said that in his judgement there was a "significant risk of Roberts causing further offences in the realm of intimate relationships. Under these circumstances in my judgement this calls for an extended sentence to protect the public from such serious harm".
He also said: "There is in my judgement a clear and palpable link between taking some types of steroids and a loss of temper that is triggered by absolutely nothing in relation, followed by a disproportionate use of force and violence."
Roberts was sentenced to an extended eight-year jail term. He must serve two-thirds before his release plus a three-year licence period. He was also made subject to a restraining order preventing him from contacting the women in any way for 15 years.
Five other offences were allowed to lie on file.