Matthew Mcconaughey was stunned when girlfriend Camila Alves managed to hike up a hill without getting dirty.

The actor is a fitness fanatic and says one of his favourite pastimes is to go hiking and when he took Camila to French Polynesia he was amazed at how she coped on their trail as she was dressed so inappropriately.

He said: "We went up to 3,000 feet and I had on hiking shoes and I was all set up and ready to go. Camila was wearing Havaianas sandals and a white skirt. I came down to the bottom of that hill afterward and had blood on me, all muddy ... and that girl didn't have a speck of dust on her."

As well as hiking, Matthew - who has children Levi, two, and 13-month-old Vida with Camila - also keeps his body in top shape by using heavy rocks.

He explained to Men's Fitness magazine: "It's not as simple as it seems. You shift the weight from high above your head, in your right arm, then your left, then rest it on your shoulders, adding more weight to your back, then your legs.

"You get a full-body workout just by finding out how many positions you can manage without having to set the weight on the ground. You also discover the stronger and weaker spots in your physique."