Finlay Robertson’s debut play Strong Arm takes a look at Roland Poland, a 20 stone young man, as he takes on the mental and physical challenge of changing his body from fat man to bodybuilder. A somewhat comic, somewhat tragic, look at the desires and punishment that bodybuilders put themselves through, Robertson’s play is as powerful as it is gruesome. Playing the role of Roland himself, Robertson performs with heart and candour, taking his audience through his life of protein shakes and his morphing body.

Strong Arm is at first difficult to get into – there’s something about Robertson’s writing that takes time to sink in – but once you join him on his protein diet and pumping guns of steel, you can’t help but be won over. Underlying this story of fat boy to steel man is the terrifying side effects and conditions that bodybuilders put themselves through. From blood in the urine to uncontrollable sexual discharge, the body is destroyed before it is repaired, muscle after muscle. Strong Arm acts, at times, as a lesson for those of us not pumping away at the gym – to gain muscle we must tear fibres and rebuild, again and again, putting our body under stress and causing both physical and mental strain.

Where Strong Arm works is in its ability to make the audience unsure whether to laugh or be serious. The thin line that Roberton’s writing treads makes for this uncertainty, and as the character of Roland gets caught in the routine of gym – eat, wank, sleep, gym, eat, wank, sleep – the darker side of the muscle-building world is revealed. To feel pain is to be achieving, and to achieve you must be in pain.

Roland’s story spans the length of the childhood torment of being overweight to the mental drive of becoming someone else altogether. It’s a compelling, strange but strong production that demonstrates Robertson’s ability both as a performer and as a playwright. It feels as if Strong Arm is somewhat of a challenge too – with Robertson being of average build yet having to vent this anger and attempt to emulate the qualities of a body builder (especially at the end during a Mr Britain contest, complete with speedos), it is a brave performance. It doesn’t completely blow you away, but it does leave you wondering whether joining a gym to get rid of puppy fat would actually lead to harming your body more. A small note of caution by Robertson is given: to change your body is to change your very self or being. Are you prepared for that?

**** – 4/5 stars

Strong Arm is playing at Underbelly as part of the Edinburgh Fringe Festival until 26 August. For more information and tickets, see the Edinburgh Fringe website.