Hugo Chavez has led his biggest rally since he was diagnosed with cancer a year ago, seeking to stage a show of strength as he heads into a re-election campaign to extend his 13 years of socialist rule.The Venezuelan president stood on top of a lorry in Caracas on Monday as it drove through huge crowds of supporters who cheered and threw roses and confetti as he made a dramatic re-entry into the public eye after months of keeping a low profile during cancer treatment.The 57-year-old Chavez, a former army paratroop commander first elected in 1998, is seeking another six-year term in the October 7 presidential vote.The rally in the Venezuelan capital was all the more important after his opposition rival, Henrique Capriles, put on a show of youthful vigour on Sunday by leading a 10km march with hundreds of thousands of supporters to register his candidacy."I give this to you with a promise to fight, to battle, and of course to win,” Chavez said as he handedelectoral officials his plan for government.Walking with difficultyChavez had entered the building appearing to walk with some difficulty, hand in hand with two of his daughters.Outside, several giant inflatable Chavez dolls waved their arms above the crowd as the president’s fans danced to music pounding from speakers. Hundreds of buses that ferried his followers to Caracas stood parked in side streets.In a Twitter message, Capriles said: "This candidate isn’t walking, he is out of gasoline! ... A better future of progress is coming!”Any turn for the worse in Chavez’s health could mean the end for his movement. That would be a blow to global leftist leaders who see him as an inspiration, but a boon to investors seeking free-market reforms in Venezuela and oil companies keen on tapping the world’s biggest crude reserves