What started out as a jog along her regular running path resulted in a woman believing she was never going to get to see her children again as a stranger violently assaulted her.

The 50-year-old woman, from Salt Lake City in the United States, was out running along one of her favourite paths on March 19, just as she had done hundreds of times before.

She was about a third of the way into her run when everything changed.

The woman, who cannot be named for legal reasons, told the 3rd District Juvenile Court that she came across a teenage boy with a scooter who asked if he could borrow her phone, The Salt Lake Tribune reported.

"It seemed like he needed help. So I stopped," the woman said.

The woman quickly realised that something was wrong when she noticed the teen, 15-year-old Rainier Craig Peterson, was only pretending to make a phone call.

She demanded her phone back and tried to take the device from him but in what seemed like a split second the boy grabbed her arm and dragged her off the path into a ditch.

Peterson pinned the jogger down and began punching her before reportedly strangling the woman and telling her "You will die today".

In a desperate bid to stay alive the woman said "I will do whatever you want", as she felt herself slipping out of consciousness, she told the court.

The teen then proceeded to violently sexually assault her three times, with the woman claiming she thought she was going to die as he tightened his grip around her throat again.

"I was so quickly passing out and so desperate for air," she woman said.

"And again, realising, 'I cannot believe this is how my kids are going to lose their mother. I cannot believe this is how it ends for me'."

The woman claimed she tried to run away from Peterson multiple times but he continued to beat her so she could not escape.

She testified that at one point the teen smashed a glass bottle over her head before attempting to shove glass in her eye and threatening to slit her throat if she resisted.

The 50-year-old eventually managed to escape on her third try and she ran and sought the help of a passer-by who called the police.

Peterson confirmed his victim's claims, admitting to stopping the woman by asking to borrow her phone before repeatedly sexually assaulting her.

"I hit her and dragged her into a ditch and forced sex upon her," he told the judge, Fox13 reports.

Police raided the teen's home after the attack and found bloody clothing that had DNA that matched the victims.

A rape kit revealed that the DNA found on the victim also matched Peterson.

The teen faced both juvenile and adult court where he pleaded guilty to aggravated kidnapping and aggravated sexual assault as part of a plea deal.

The deal means that Peterson will not be sentenced for the sex assault conviction until he has served his time for the kidnapping charge in juvenile detention.

He will likely face the sexual assault conviction when he turns 21, when he can be trialled as an adult.

A sexual-assault conviction in adult court carries a possible sentence of 15 years to life in prison, but prosecutors agreed to recommend that the minimum be lowered to 10 years.

If you're in danger NOW:
• Phone the police on 111 or ask neighbours of friends to ring for you.
• Run outside and head for where there are other people.
• Scream for help so that your neighbours can hear you.
• If you are being abused, remember it's not your fault.

Where to go for help or more information:Where to go for help or more information:
• NZ Police
• Help Auckland 24/7 helpline 09 623 1700
• Rape Prevention Education 
• Wellington Help 24/7 crisisline 04 801 6655, push 0
• Male Survivors of Sexual Abuse
• Women's Refuge: Free national crisis line operates 24/7 - 0800 REFUGE or 0800 733 843 www.womensrefuge.org.nz
• Shine, free national helpline 9am- 11pm every day - 0508 744 633 www.2shine.org.nz 
• Shakti: Providing specialist cultural services for African, Asian and Middle Eastern women and their children. Crisis line 24/7 0800 742 584
• White Ribbon: Aiming to eliminate men's violence towards women, focusing this year on sexual violence and the issue of consent. www.whiteribbon.org.nz