Festival review: Strong Arm; Underbelly Cowgate (venue 61)

As an adult he finds an outlet for his pent-up self-loathing and hatred for the world when he hits the gym and transforms himself into a beefcake extraordinaire, with his sights set on the Mr Britain bodybuilding competition.

But can any amount of weightlifting, bench pressing, powdered supplement shakes and protein bars alleviate the sadness, fear and anger of the confused little boy beneath?

Written and performed by Finlay Robertson, Strong Arm is among the tightest one-man plays you’ll see on the Fringe this year, full of pathos and sharp wit. On a sparse stage set, he builds a dense and engrossing character piece, the ubiquitous tale of the schoolboy loser determined to show the world.

As Poland’s obsessive compulsion with bodily improvement grows, he starts to dwarf his peers and enemies in strength and stature, and develop warped superhero fantasies. Bodybuilding becomes a kind of neurotic fetish that corrupts his sexual mechanisms and desires.

He hangs on the words of his idol Arnold Schwarzenegger, who has spoken of how “the pump” – the euphoric swelling sensation weightlifters feel as blood floods into their muscles after a heavy workout – for him is better than sex. A recording of Arnie’s voice explaining as much is used to great effect.

Poland finally finding love would be an obvious redemptive endpoint for Robertson’s story, and he seems to be working towards such a conclusion as Poland shyly builds a relationship with his yoga masseuse. But his fearfully flawed antihero craves much greater validation than that.

When Robertson bravely strikes poses in a pair of skimpy bodybuilder pants at the play’s finale, the fact the actor’s less than weightlifterly physique comes almost as a surprise just serves to demonstrate how convincingly he has inhabited his character throughout the preceding hour.

Rating: * * * *

Until 26 August. Today 4:10pm.