MEXICO CITY (REUTERS) - Mexico's presidential front-runner Andres Manuel Lopez Obrador on Friday (May 18) laughed off media reports he was in poor health, saying he was "100 per cent" fit and could "stand on one leg."

The 64-year-old Lopez Obrador, who suffered a serious heart attack in late 2013, has for months held a clear lead in opinion polls for the July 1 presidential election.

Columns in newspaper El Financiero as well as social media reports this week said Lopez Obrador's heart and back required regular treatment, but the veteran leftist said on a campaign stop in southern Mexico he was in excellent health.

"I can even stand on one leg," Lopez Obrador told supporters in the town of Huajuapan de Leon in the state of Oaxaca. "Thanks to science and the creator, I'm 100 per cent. My adversaries are very nervous because we're still advancing," he added.

Some recent voter surveys have shown Lopez Obrador's advantage in the race growing over his second-placed rival, 39-year-old Ricardo Anaya, who heads a right-left coalition.

The silver-haired Lopez Obrador, a former mayor of Mexico City, has said he takes a "cocktail of pills" to control his blood pressure. However, he has kept up his relentless schedule of rallies running in his third presidential campaign.

Reports about his health surfaced before a second televised presidential debate on Sunday (May 20).