By Peter Gould BBC News Online

Despite his frailty, Pope John Paul II is determined to continue his travels, taking his message to the world.

On Tuesday he set off from Rome on a transatlantic journey that will take him to three countries in 10 days.

His first touchdown will be in Toronto, where he is taking part in the World Youth Day.

Young people from 170 nations will be attending, and the Pope will be making three appearances, the climax being a huge open-air mass which is expected to draw a crowd of three-quarters of a million.

A cross as tall as a 10-storey building has been erected in a Toronto park. Critics of the visit say it is costing millions of dollars of taxpayers' money.

Strains

Despite growing concern over his ability to withstand these arduous foreign tours, the Pope was determined to go ahead with the trip to Canada.

A huge cross has been erected for the papal mass

He enjoys nothing more than meeting young people, and seems to take strength from the enthusiastic reception he receives.

But the Vatican has been careful to allow John Paul II plenty of time to recover from the strains of travelling and attending the various events.

He will be staying at a Catholic retreat on Strawberry Island, a tranquil setting on Lake Simcoe, near Toronto.

A boat will be at his disposal for sightseeing on the lake, and a golf buggy will be available for trips around the 45-acre island, which is owned by a religious order.

But the Pope will scarcely have got over his jet lag before he is off again, first to Guatemala, and then to Mexico. He will be creating new saints in both countries, and huge crowds are expected to turn out.

"Stay home"

In Mexico, there is excitement over the papal visit, but many Catholics are concerned about the possible impact on the Pope's health.

The Pope's travels

95 overseas trips 130 countries 604 cities 552 days on road 1.1million km (698,000 miles)

In an opinion poll conducted by the newspaper Reforma, no fewer than 58% of Catholics thought it would be better for the Pope to stay at home.

And 52% said they thought popes should retire after a certain period in office.

In recent days, the Pope has been following the advice of his doctors by resting at his summer villa at Castel Gandolfo.

In a break with tradition, he has conducted his weekly audience in the courtyard, rather than face a helicopter trip to the Vatican.

It is another indication of the Pope's physical decline. During recent public appearances his speech has been slurred and difficult to understand.

He is suffering from the symptoms of Parkinson's disease, but although his body may be weak, aides insist his mind is as sharp as ever.

Emotional

Suggestions that he might retire have been dismissed by those who know the 82-year-old pontiff. They say his attitude is simple: he was given the job by God, and will continue his ministry until the day he dies.

The Pope at his audience in Castel Gandolfo

John Paul II places great importance on his foreign trips as a way of showing himself to the faithful and spreading the message of the gospels.

So far - not counting this latest journey - he has completed 95 overseas tours, visiting 130 countries.

In all, he has been on the road 552 days, and has covered 1.1 million kilometres (698,000 miles).

That is the equivalent of circling the world 28 times.

And if sheer willpower continues to overcome his frailty, this will not be his last trip. In August, he wants to return to his native Poland.

It is estimated that an open-air mass, being planned in Krakow, could draw a crowd of two million people.

It would be an emotional visit for the Polish pope and the people of his homeland.