What's allowed Philadelphia Flyers forward Jaromir Jagr to remain an effective player in the NHL as he reaches his 40th birthday?Clean living, he says -- no smoking or drinking alcohol -- but he does admit to one vice."I like Diet Coke," he says with a laugh. "I even drink it during a game. I like Diet Coke. No vitamins, nothing ... Diet Coke."Oh, if it were only that easy.Hard work on and off the ice has been a hallmark of Jagr's career since he first arrived in North America."We had to kick him off the ice almost every day," Joe Mullen , a teammate when Jagr first arrived as a rookie in Pittsburgh and currently an assistant coach with the Flyers, told NHL.com. "He just loved to stay out there and just work."That holds true today, as Jagr occasionally will skate and work out at the Flyers' practice site late at night; in fact, getting 24-hour access to the practice facility was a requirement in his contract.He joked earlier this season that he enjoyed the late-night ice time because "the ice is free."In reality, it's something Jagr said he's done at previous stops in his NHL career, and something he feels he has to do now that he's turning 40."You have to practice a lot harder. I know that," he said. "You've got to love the game so much that even if you're tired, you still have to go there. Sometimes I don't want to go run at night, but I know if I don't do it, tomorrow I'm going to feel worse than I did the night before. That's what's pushing me."When you don't fear anything and you think everything is going to be OK, then what's the reason to do it? When there's fear that you're going to feel a lot worse, that's pushing you. And I know if I don't do it today, tomorrow's not going to get better. There may be a five-percent chance you're going to feel better (by taking a day off), but there’s a 95-percent chance you're going to feel a lot worse ... and you still have to do it the next day anyway. I understand that, and it's tough to do that, especially when you struggle. You have to have the will to do it, even if your body doesn't want to. You still have to push yourself and work even harder. If I'm not able to push myself, I think I'm going to quit. When you feel tired and you don't push yourself, it's time to retire because you're not going to get better. There's no miracles. You're not going to wake up the next day and feel 10 years younger."Jagr said he has no interest in sticking around in the NHL based on his reputation, saying he'd rather go play in the Czech Republic if he doesn't feel like he can stick with today's NHL players. But he wants to stay at that NHL level, and spends his extra time working to keep his skills as sharp as he can. His off-time activities include skating in a weighted vest or using a weighted stick to work on his puckhandling."If you're a (star) player and you want to keep playing like that player and you've been doing things to be that player, you want to keep doing them," he said. "Once you lose it or don't want to do it, you're not going to be the same player. Once you taste something, if you're a good player and work harder than other guys and you can see you're getting better and better ... you kind of fear that once you stop doing that, you're not going to be the same player. That's why you keep doing that, because it's working. I've always had that."