Koh Lanta, Thailand: dial the clock back to prehistoric times and get back to nature's basics

The world is a watercolour of indistinct blues and greens, my heart hammering from a brief but intense swim. Saltwater stings my eyes – I didn't grab enough air before diving.

I can see Vic beneath me, sinking. I kick harder, my lungs burning, the water pressure pushing daggers into my ears. I reach him and lunge for the surface. Kicking back to the boat, I keep his neck locked firmly in my elbow as he taught me. "Remember to calm your breathing, as we spoke about on the boat," he whispers. You can't rescue a drowning man if you yourself cannot breathe – just one of many practical yet prehistoric lessons I'm about to learn.

"Some former human species were stronger than we are today; stronger than the strongest athletes," says Erwan, back on the beach. "When you're a kid, you're always told: 'Don't yell, don't move.' Whenever we have this primal exuberance, this expression of energy that we have in ourselves, it's repressed to the point that it's suppressed – you have to stand right, be polite, be silent, then you're a good kid." He speaks with passion. "You're not supposed to be a good animal; you're not supposed to be powerful. We become civilised, domesticated and I believe that makes us weaker." I, along with half a dozen Europeans, Americans and an Australian, have come to the island of Koh Lanta in Thailand's Andaman Sea to experience MovNat – a unique approach to fitness based on the lifestyles of our cave-dwelling ancestors.

According to the creator of MovNat, launched in 2008 and based on the historic French 'Methode Naturelle', modern mankind has evolved into 'zoo humans' – dangerously detached from our natural world. As a result, so the philosophy goes, we suffer physically, mentally and spiritually. Like animals born in captivity, we must be rehabilitated before we can 'get back to natural living' and be 'strong, healthy, happy and free,' but what exactly does that mean?

For founder Erwan Le Corre and instructor Vic Verdier, a former member of the French Special Forces, it means examining our contrived, orderly world and how we fit into it – not as the humans we think of ourselves as, but as the human-animals we really are. "You don't see stiff animals in nature; they are all flexible, they all can move," Vic says after a tough work-out involving running, carrying rocks and then crawling underwater until your body begs for oxygen. "Some are very feline and we like that because they are so supple, so flexible in their movement" – the very essence of the wild, pre-zoo hominid.