A big man needs a big workout - just take a look at these guys who appear to be building more than muscles.

These towers of strength are part of a mighty advertising concept from young U.S. designer Michael Griffith.

The unofficial mock-ups for American fitness chain Powerhouse Gyms feature huge posters of bodybuilders who seem to be using construction sites as pieces of gym equipment.

One appears to show a muscleman using winches either side of a tower block as a multi-gym, while others seem as if the oversized fitness fanatics are utilising cranes as exercise machines.

Another clever idea sees a weightlifter appear to be lifting the roof of the tower from the ground. Michael, 22, of Crawfordsville, Indiana, explains: "Once you have a few levels of the building constructed, the ad would be placed up, showing a preview of what's to come. As the weeks go by and the building continues to go higher and higher, you start to see more of the body builder."

In what Michael describes as a "moving viral", he also has a bodybuilder doing a leg press with the back door of a garbage truck. When the door opens and close, onlookers will get the impression that the man is exercising his lower body.

Creative Michael got the idea of linking bodybuilding with tower block construction as they both "take a lot of time and hard work to build something so large".

"I thought of elements that are found in a gym and the elements that are associated with a construction site," he explains. "Most weight machines work with cables and are the biggest asset to building muscle. I tied these two elements together and out came the final concept. The message gives an impression that the body builders are doing the tough work to get the building constructed."

Michael is currently looking to break into the ad business with the help of his eye-catching designs.

You can check out his work at http://www.mgadvertisingdesign.blogspot.com/

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Michael Griffiths/Rex Features
Story by Dean Murray