Gyms where he trains in Horsham and Pulborough have been supporting him by selling t-shirts ahead of the big day on Sunday, July 25.
Charles, who lives in Southwater, will run a half marathon, go straight into the u90kg Strongman, then finish the day with a second half marathon.
He said: “I couldn’t think of anything more testing than having to push the boundaries of fitness, strength, determination and, more importantly, community support.”
Last year, Charles and his Woodpecker WOD team raised more than £2,500 for West Sussex Mind with a skateboard marathon.
Charles said: “The only difference this year is that I’ll be doing it alone, with as many people as possible joining me for different sections of the run and get a crowd along to the Strongest competition.”
Charles will be dividing the money he raises this year between West Sussex Mind and StrongMen, a charity which tackles emotional and mental health issues brought about by bereavement.
He said: “I thought of it a while back, a Strongest Marathon that would push my physical capabilities but, even more so, test my mental endurance.
“I’d like to continue support the amazing charity West Sussex Mind as the work they are doing locally within our county and our community is priceless support for those who are brave enough to ask for support and help with their mental health.
“I am sharing it with StrongMen, who are there to support men following bereavement. Grief can cause severe mental and phsyical health conditions which are often overlooked and often ignored, especially in men.
“This charity means so much to me for so many reasons. On December 19, I did a workout with one of the co-founders, Efrem Brynin. We chatted away about our dislike of running, getting through it together and one foot in front of the other. We needed each other, just to complete a horrible workout, so imagine what support you would need going through bereavement without knowing you do.
“Only 12 days later, on December 31, I found out exactly what it means to be suffering the loss of someone so close. Completely out the blue, a massive influence and incredible man in my life was taken from us with no warning.
“I’d had 13 Christmases in a row with this family and because of Covid we couldnt this year, and now without knowing it, there was never going to be another Christmas together.
“So, it’s fitting this year we support both charities and more importantly, get people talking.”
Visit www.justgiving.com/crowdfunding/woodpecker-wod-strongest-marathon for more information and to make a donation.