Natasha Hamilton can't run for more than five minutes.
The Atomic Kitten singer is giving up smoking for Stoptober this month and hopes she will be able to do a marathon next year if she manages to stay away from nicotine.
Speaking exclusively to BANG Showbiz, she said: "I want to be smoke free for 28 days and then once I've hit that 28-day mark, I know I'm going to be twice as likely to give up.
"I've started with my personal trainer and one of my big targets is to be able to run. I can literally run for about five minutes and my lungs feel tight, it's not a comfortable experience and it's because I am smoking.
"A few years back I did a half marathon and I could not do that right now. Next year if I am smoke free I could do that again."
The 34-year-old singer - who has Josh, 13, Harry, 11, Alfie, six, and 24-month-old Ella - is under no illusion that it will be easy, but is determined to stop as she is fed up of being tired all the time.
She said: "I've tried before, I know exactly what I am letting myself in for. I know it's not going to be easy. I am so ready. I am sick and tired of feeling like rubbish, having a sore throat and not having energy."
Natasha is also quitting smoking because she is going to be performing in a theatre production of 'Aladdin' at Christmas for six weeks, which will be "intense" on her voice.
She added: "I sit there sometimes and think why am I smoking? It's an addiction and you get on a slippery slope. I'm looking forward to belting it out. I am doing six weeks of intense singing and speaking. Three shows a day some days. So I need to have my voice on top form."
Natasha is to handpick her favourite tracks to help motivate quitters to stop smoking throughout Stoptober.