Texas [US]: Argentina's FIFA World Cup-winning icon Lionel Messi seems to have no off days, even on his birthdays, as he sweated it out in a gym on his 39th birthday on Wednesday.Messi turned 39 on Wednesday, entering a new chapter, a new year of his life as the FIFA World Cup's top goal-scorer of all time.On his Instagram, Messi posted a video of himself doing a full-intensity workout, focusing on his upper body, arms etc.Messi-led Argentina has made to the round of 16 in the FIFA World Cup, and their last group stage match against Jordan will take place in Texas on June 28.Messi became the highest goal-scorer in tournament history, as his brace guided Argentina to a win over Austria. After scoring his first World Cup hat trick in the campaign opener against Algeria, Messi continues to make headlines with his record-breaking ways. He has scored all his side's five goals in the tournament.Also Read | Lionel Messi turns 39: A look at age-wise distribution of goals scored by Argentina iconAs per OptaJoe, Messi is just the second player in the tournament history to score his country's first five goals in a single edition, along with Oleg Salenko for Russia in 1994.During the match, Messi, set to celebrate his 39th birthday on Wednesday, had 71 touches, the oldest striker since 1966 to have 50-plus touches in a WC match.Also Read | Messi and Mbappe romping through World Cup with dazzling display of history-making goalsMessi's brace not only won his side their clash against Austria, but also brought him above Miroslav Klose (16 goals) as the leading goal-scorer in the history of the FIFA World Cup, with 18 goals. He also equalled the record of France's Just Fontaine and Brazil's Jairzinho by putting his name on the scoresheet in his sixth successive WC game.Messi set a new record for the most wins by a player in FIFA World Cup history, surpassing German legend Miroslav Klose's tally of 17 victories, with his 18th WC match win.