LONDON - Novak Djokovic's Wimbledon title tightened the iron grip of the sport's big four, who have now claimed 40 of the last 45 Grand Slams, and delivered another crushing blow to their struggling heirs. Since Roger Federer, who saw his hopes of a record eighth title at the All England Club ended by Djokovic in another Centre Court epic, won his first Wimbledon crown in 2003, only five men have managed to loosen the stranglehold. Andy Roddick (US Open 2003), Gaston Gaudio (French Open 2004) and Marat Safin (Australian Open 2005) have all retired.Juan Martin del Potro, the giant Argentine, managed to win the 2009 US Open as a raw 20-year-old but has struggled with wrist injuries ever since playing catch-up, while Stan Wawrinka claimed this year's Australian Open against a clearly injured Rafael Nadal. In the last 11 years, the tune has not changed with Federer winning 17 majors, Nadal, 14, Djokovic has now gone to seven while Andy Murray, once a serial loser at the majors, has two.At this year's Wimbledon, much was made of the likes of Grigor Dimitrov and Milos Raonic as the vanguard of the next wave, but both were firmly put in their place by Djokovic and Federer respectively in the semi-finals. Nadal hit the nail on the head in the immediate aftermath of his fourth round loss to Australian 19-year-old Nick Kyrgios. The Spaniard was destroyed by the whirlwind from Canberra but, just as he predicted, the storm eventually blew itself out in the next round."The sport is a mental part a lot of times. Everything is a little bit easier when you are arriving," said Nadal. "But when you are there yourself (at the top), the people start to see the negative things in your tennis." Nadal was also right also to point out that when he was 19, he was already a major champion having captured the first of his nine French Opens in 2005. For Nadal and Djokovic, the problem for the much-vaunted next generation is not on their racquets but what's between the ears."When I was 19 I was here already playing these kind of tournaments and competing well. Now it's very strange that young players are coming so late," said the world No 2. Dimitrov and Raonic are both 23, but Federer was 21 when he won Wimbledon for the first time and Nadal was 22 with his 2008 win in London. Djokovic was 24 when he took the first of his All England Club titles in 2011 but he was only 20 when he won the first of his seven majors in Australia in 2008. In a further worrying sign for the likes of Dimitrov, Raonic as well as 24-year-old Kei Nishikori, the last man to win Wimbledon before the emergence of the big four was Lleyton Hewitt in 2002 and he was only 21. The new generation are not about to be handed a magic potion, said Djokovic. "There are no secrets," said the new world number one. "The regime of practice on the court and in the gym, off the court, physical preparation, is the same as it has been for many years." Federer would have been the oldest Wimbledon champion of the modern era if he had defeated Djokovic. But the Swiss believes that outside of the elite of the game, there is little to be concerned about. "I don't feel a huge threat. There's many good players from 5 or 6 to 20. But they're also somewhat exchangeable from 30 or 40," Federer said. "Clearly there's never a guarantee. But I do believe the top guys are the ones we know and who are still going to be deciding outcomes of the bigger tournaments, like the Masters 1000s and the Grand Slams." Federer backed up Nadal's belief that the current younger generation may just not be good enough to last the pace. "We all made the breakthrough much earlier than most of the guys," Federer said. "Rafa was incredible as a teenager. I was better at 21. That's when I started to make my rise. "The other guys we're talking about are all 22, 23 and have been already on tour for five years."