COMEDIAN Des McLean is not laughing as he squats down, the 22kg Bulgarian sandbags draped across his shoulders causing his knees to buckle like they were made of Bacofoil.
As he tries to rise for the 20th time, with the Rocky theme Eye Of The Tiger playing in the background, the sweat-soaked stand-up simply can't any more.
A word emits from his lips he wouldn't like baby son Harry to repeat one day in the school playground.
"I'm knackered," says Des, forcing a smile as he kneels on the soft-padded floor of the G1 Gym in Drumchapel. "But it will all be worth it in the end."
What is 'the end'? Former Radio Clyde favourite Des has signed up for a series of training sessions that would make Foreign Legion recruit drills seem like a visit to a pleasure beach.
But the reason for the McLean hard core training sessions with special instructor Gareth McCann makes sense.
The ex-Clyde 1 breakfast favourite is set to star as Tommy Sheridan in comedy stage play, I, Tommy, written by Ian Pattison, the creator of Rab C Nesbitt.
Yet, while Des bears a resemblance to the former politician – and he has been impersonating him for years on stage and on radio – Tommy is lean and muscular.
Des admits in recent times he's been far too fond of the lamb bhunas, with enough naan bread to feed the whole of Bishopbriggs,
"I was visiting my favourite curry house that much they decided to name a curry after me!," says Des. For once, he is not joking. There is a Duke Street curry house that sells the Des McLean Curry.
"Now, I need to look the part as well as act the role," he says of I, Tommy, which will start at the Edinburgh Fringe Festival in August and then tour the country, playing the King's Theatre, Glasgow, in November.
"Tommy Sheridan has always looked after his fitness, he's a regular boxer and football player. But I am 13st and don't want to appear as Tommy wearing elasticated trousers. So I think I need to lose the worst part of a stone."
He adds, with a laugh: "Sometimes I wish Ian Pattison had written a play about the life and times of Alex Salmond."
I, Tommy tells the story of Sheridan's rise through the political ranks, and his downfall after two headline-grabbing court cases. The play also features former Taggart star Colin McCredie as Tommy's best pal, Alan.
But can Des get down to a fighting weight?
Trainer Gareth says: "I have got Des on a running programme, with sprints, and alternating slow runs, to burn up fat. He is also doing some boxing and lifting kettle weights."
Gareth nods in the direction of a series of ropes and webbing hanging from the ceiling: "I have also got Des using the TRX suspension system, which uses the person's body weight to work against."
Des adds: "The system was designed by a Navy Seal, to enable men to develop their bodies to cope with operating in the most gruelling conditions in the worst possible terrain.
"I reckon a month of this should get me really ready for a 90-minute theatre show."
Des needs to lose 1lb a week and that means blitzing 3500 extra calories. He says: "I reckon I will do that okay. I am really determined. But training isn't enough, so Gareth has also put me on a new diet.
"I knew I would have to cut down on the curries and the cheeky wee beers at the weekend and eat sensibly. But I had no idea I would have to jettison the toast and coffee for breakfast and tuna sandwiches for lunch.
"Gareth says I need to cut out the refined carbs, so I am on the porridge, pumpkin seeds and I drink green tea."
Des, who recently appeared on STV show Too Good To Waste, adds, smiling; "I didn't fancy the idea of porridge. My granny used to fill it with more salt than you would find in the Dead Sea and I have been dead against it since.
"But my wife Alison made some and it didn't taste half bad."
Des did not waste much time after five successful years at Radio Clyde, which produced two Sony awards, and four top selling CDs of his show's 8:10am sketches.
He moved on to working for the One Show on BBC and also STV, and he toured New Zealand with his stand-up show during the winter. He also became a dad.
"Since Clyde I am getting a chance to do things I could not before, I am enjoying doing more telly and touring New Zealand was amazing.
But playing the part of Tommy will be the ultimate challenge, I can't wait."
The comedian adds with a wry grin; "If Sylvester Stallone can still look fit at the age of 76, or whatever he is, there is every chance I will be able to pass for Tommy Sheridan."
Des's final stand-up comedy show before his run with I, Tommy starts is at the Motherwell Civic on June 30. For updates follow Des on: Twitter@desmclean