Mind prompted end for Cowboy Johnson In the end, it was the mind and not the body that was no longer willing for battle-hardened North Queensland Cowboys backrower Dallas Johnson. Given he at one stage suffered seven serious head knocks in as many seasons, few would probably be surprised Johnson is drawing the curtain on his impressive NRL career at the age of 30. But it was a shock when the former Test lock on Tuesday revealed the reason behind hanging up his boots at the end of the 2013 season. "Physically I am not too bad, I could go on again if I chose to," he said. But mentally I have had enough. It is time to move on and look for a new challenge. Growing up in Herberton in far north Queensland, Johnson's NRL dream must have seemed just that. And with the dimensions more suitable for a halfback - his 183cm frame has now bulked up to 93kg - Johnson would have been forgiven for thinking he would never fulfil it. No wonder Johnson said he would walk away from a career that boasted a 2007 Test and 12 Origins for Queensland a happy man. "For a bloke of not huge stature, playing in the middle and playing pretty tough I am very content with my career," Johnson said. Those who witnessed some of Johnson's sickening head knocks would also be surprised his NRL career lasted so long. In 2009, Johnson admitted he had suffered two serious concussions and up to three low to mid-range blows to the head since 2004 playing for Melbourne. In 2011 alone he suffered two more serious head knocks including horrific contact with then Sharks prop Kade Snowden's knee, prompting cognitive testing. In the end, Johnson's ankle prompted him to be rested this season with the Cowboys but the tough as teak lock admitted he couldn't get his head around another season. "It would not be fair on myself, the club or my teammates if I went on next year," he said. Johnson enjoyed a 157-game stint and four straight grand finals with Melbourne (2003-09) before linking with English Super League's Catalan Dragons (2010) then the Cowboys. At North Queensland, he has set club records for most tackles in a game (64) and a season (1006 at an average of 41.9 per game). "It's a sad day," Cowboys coach Neil Henry said. Pound for pound you wouldn't get a more competitive player. And he'll leave a legacy. To kids growing up it says if you are willing to work hard you can realise your dreams and go on to play not only NRL but for your state and country.