Lucy Mecklenburgh says Tour De Celeb has created a lot of "blood, sweat and tears".
The TOWIE star is one of eight celebs who have signed up to tackle "the toughest physical and mental challenge on TV".
The four-part series kicked off last week and sees the all star celebrity contestants preparing to take on the L’Etape du Tour in France.
Joining Lucy on the line up are model and TV presenter Jodie Kidd, Made In Chelsea's Hugo Taylor and England rugby legend Austin Healey.
Also taking on the challenge are Olympic Gold medallist Amy Williams, England cricketer Darren Gough, presenter Angellica Bell and dancer Louie Spence.
Lucy admitted: "It was hard for Angelica and me because we were starting from scratch. We'd barely been a bike.
"I underestimated how hard it as going to be. It's been really tough. A lot of blood, sweat and tears - on my part, anyway."
However there have been positives.
"I've got new muscles in my legs," said Lucy. "You're allowed to eat as much cake as you like. It's amazing! it's nice to be able to indulge in what you want, like having a big bowl of pasta. It's something I don't usually do."
And speaking ahead of tonight's latest episode, the TOWIE star added: "I just want to finish. I don't care about beating anyone.
"When I signed up I thought it would be great to win, but once I started the process I realised how tough it would be to even finish."
Tour de Celeb airs Monday nights at 7PM on Channel 5.