'Maximum limit'

Despite his body convulsing with hundreds of contractions, and in almost unbearable pain, Maricic said he recovered with no long-term effects.

Brief intestinal bleeding and a massive headache soon passed, and he is already eyeing up another record.

Russia's Alexey Molchanov holds the record for the deepest freedive with a variable weight, descending 156 meters with the weight before returning to the surface without it.

Maricic is aiming to beat that within two years, pushing to reach 160 meters.

But even for the seasoned diving instructor, it will take exceptional fitness and preparation to withstand the intense pressure of such a dive without oxygen.

"Whenever I think that I've got all the answers and pushed my body to the maximum limit, a new window of opportunity opens and new questions arise," he said from a pool in the Croatian port city of Rijeka.

Maricic heads the Croatian branch of AIDA — one of the two international bodies that govern freediving.

Reflecting the sport's fierce rivalry, the other governing body once accused him of misconduct.

The Croatian, who has never failed a doping test, has strongly denied any wrongdoing.

In the zone

Growing up on Croatia's coast, Maricic became passionate about the sport early in his life, diving in the Adriatic Sea from as young as three.

A devotee to high-performance sports, he began competitive freediving just nine years ago.

"The very act of going underwater triggers a series of physiological processes that pull you straight into a 'zone'," he said.

"Even on the first day of a beginner's course, the mind has no choice but to narrow its attention to one thing — where you are and what are you doing."

He has racked up numerous top international rankings and national records for his diving prowess.

But his time in the sea has also made him a witness to the "horrific" changes to the Adriatic of his childhood and a vocal advocate for ocean protection.

"If we don't protect the living organisms, and if we don't raise awareness about that, we're not looking at a bright future," said Maricic, who is also an ambassador for marine conservation group Sea Shepherd.

"We're not talking about 50 years, or 100 years. We're talking about changes that can happen in the next 10 years."

AFP