Chelsea's midfield enforcers John Mikel Obi and Michael Essien are back in full training with the Blues following frustrating campaigns last term.It's a welcome sight for Stamford Bridge regulars, after Nigeria international Mikel was sidelined in April by ankle and knee injuries, while Essien made a miserly 13 Premier League starts during 2009-10. Although Chelsea claimed a domestic double last season, Mikel was forced to sit out the end of season run-in and FA Cup final, before suffering another blow when his injury problems forced him to return home from the World Cup before the tournament had even begun. However, the 23-year-old has been in rehabilitation since and insists the problems, which required minor surgery, are firmly behind him. "It was really frustrating to miss out [with Chelsea] but at the same time I was obviously happy that we won the Double," Mikel told Chelsea's official website. "Since I came home from South Africa I've been here, working hard on my knee and making sure I am ready for the start of the season. I'm fully involved now with pre-season training and have started the double sessions. "It is going really well, the training is good and the weather has been fantastic, and we are all working hard. I look forward to the rest of the squad joining us and I hope it can be another good season." Mikel's team-mate at Stamford Bridge, Michael Essien, is in a similar position, having not played since December due to injury. Like his fellow midfielder, 27-year-old Essien is close to full fitness and has had complete involvement in training. Despite Chelsea letting Deco, Michael Ballack and Joe Cole leave this summer, competition for places will still be fierce in Carlo Ancelotti's engine-room. Although, Mikel is not overly concerned. "I don't know, I'm working hard and whatever decisions there are, are for the manager," he added. "It is very good to have [Michael] Essien back. He has been out for a long time, and I hope we can play together in the middle, that would be great."Source: Kickoff.com