Jennifer Lopez has been training hard for a triathlon, and it certainly showed as she arrived at a charity event in Colorado last night.

The singer, who gave birth to twins Max and Emme just six months ago, put her slimline figure on display in its glory in a figure-hugging red frock.

But it appears the singer forgot to spray deodorant before leaving the house, with unsightly underarm sweat patches proving a distraction from her otherwise immaculate ensemble.

Feeling the heat: Slimline Jennifer Lopez at a charity event in Colorado last night

The 39-year-old is gearing up to take part in a charity triathlon in Malibu, California, next month, a decision she made when she was eight months pregnant.

'I was beached like a whale. I was watching TV, and I saw a triathlon and I said, "I think I could do that." ... Maybe we could raise some money and do something really great..'

Wet patches: Jennifer's sweaty underarms proved a distraction from her otherwise immaculate look

'I thought, "What can I do to make my babies proud?" I think about what they'll think about the year they were born - who I was and what I did.'

'It's important to me to set examples for them. I want to lead with my life.'

And though the race will be tough, Lopez is determined to finish.

"If I have to crawl across that finish line, then I will crawl across that finish line.'