Melbourne Heart goalkeeper Clint Bolton has revealed he believes the team has fitness problems.

Following the 4-0 drubbing at the hands of the Brisbane Roar on Saturday night, the former Sydney FC gloveman admitted that the players produced their worst performance so far due to a lack of fitness.

''They exposed us quite easily and it was through fitness and movement off the ball that [they] caught us out,'' Bolton said. ''It was a strange one. There were not a lot of positives out of the game. [We have now got] just a lot of hard work in front of us. There's no big secret as to what we have got to do, just work hard.''

Bolton said it may be the shortened pre-season the Heart experienced as they were still putting a squad together while other teams were busy training.

''Brisbane Roar certainly had a very solid pre-season, so they are a fit, young team,'' he said. ''Possibly, we didn't match them in that area. When we went down to 10 men it was a lot harder [especially] when we were 3-0 down, that exaggerated the situation. But Brisbane is certainly a fit, fit team, and well structured and one of the contenders, up with Adelaide at the moment.''