For most people who turn 80, it is the time to kick back, relax and enjoy a well-earned retirement.

But for one karate-kicking great-grandmother in Kansas, there is no letting up.

Helen Dugan, a third-degree black belt, continues to lead karate classes at the school she set up, Champs Achievers, despite passing the milestone.

Battling on: Despite turning 80, Helen Dugan, owner of karate school Champs Achievers, is not letting up

Aiming high: After earning her black belt at 61, Dugan was inspired to teach others the sport in Kansas

Iron fist: Dugan set up the class for disabled children and said it was important to 'build on their strengths'

The great-grandmother of 17 only took up the sport when she took two of her children to a class at the age of 47, the Kansas City Star reports.

She said: 'We never had karate when I was a child, so I took my sons to a class and I realised that my two skinny sons didn't need the exercise and so I got into the back row of the class.'

Her children lasted four years before as she puts it, 'they discovered girls and got married', but she 'was hooked'.

Dugan, who has been married to husband Barney for 57 years, took karate classes for 14 years, earning her black belt at the age of 61.

At the time she was also working as a nurse in the Center School District in Kansas City, in Missouri.

Leading the way: Dugan takes a hit from seven-year-old Brayden Bond during a class in Lenexa, Kansas

Listen in: The great-grandmother quiets the class as three-year-old Aiden Degnan tries to get her attention

Friendly face: Dugan has seen her class grow in the last 20 years and it now caters for more than 50 children

Jousting: Dugan takes on five-year-old Micah Jenkins using pugil sticks during one of her sessions

Inspired to pass on her expertise to others, the mother-of-five set up a non-profit karate class called Champs aimed at helping those with a disability.

Karate and other martial arts taught at the group - including judo, jujitsu, tai chi and a defensive street-fighting discipline called Guided Chaos - can improve concentration, stamina, balance, motor skills, independence and self-esteem.

She said: 'I started the group because the class I was learning in had children who couldn't keep up, so I took them aside. Sometimes it was because of learning disabilities, or it was children with ADHD.

'I then started teaching them separately.'