Before she could back out, Martha McLean had signed up for the challenge of a lifetime.

And now she is busy getting ready for a marathon trek through the Grand Canyon to raise money for a charity which has gone the extra mile for her gran.

Although she is a keen walker, Martha admits: “I realise this won’t be quite like a walk in the Holmfirth hills!”

In tackling the trek next March, Martha aims to raise at least £3,500 for the Alzheimers Society, which has helped her 90-year-old gran, Janina Cienicka.

“My gran is 90 and suffering from dementia,” said Martha.

“For a while I have been wanting to do something for AS to thank them for all their support.

“I looked at what I could do to raise money and the chance came up to do this trek.

“And I signed up before I could back out. It’s a bit of a challenge to say the least.”

Organised by the Society, the trek is about 80km and will take around five days to complete.

“It’s not so much about the distance as the terrain,” said Martha, who is 35 and lives at Wooldale, Holmfirth. “We go right down to the canyon floor. We have a guide and camp along the way.

“I am determined to do it.”

To prepare, the busy mother of three is doing more walking with the family’s energetic dog and has upped other forms of exercise.

Her children - Annie, 9, Ruby, 8 and Charlie, 4 - are with mum all the way. “They enjoy coming on the walks with me,” said Martha, who works as a research assistant at the University of Huddersfield.

Husband Johnny is also very supportive. “He is fit and active and usually the one doing the challenges, so he is pleased I have set myself this goal,” she said.

Martha says she has had lots of support from the community and the Tolson Grange care home in Almondbury where her gran lives.

“I owe it to all those who have faith in me to do this,” she said.

If you'd like to sponsor Martha and help the Alzheimers Society please visit www.justgiving.com/martha-mclean