"It's not about competing against other people," she says. "It's about being at war with me ... it's like you get a twisted sort of kick out of it."
Hidden Lives: Super Size She (Five, Monday), followed the Cornishwoman on her pumped-up path to Las Vegas. I don't want to succumb to knee-jerk prejudice - the men, too, look like something on an anatomist's slab. But she sounds like a bloke and she's got a five o'clock shadow. She's like a bulked-up Pauline Calf.
She has one conventionally feminine feature. Well, two. But it turns out that if you see a bodybuilder with anything remotely resembling breasts, they're implants. Breasts are fat, and fat is the bodybuilder's enemy.
Joanna, who lives in California, has her regular check-up with her nutritionist, who wields the skin calipers to measure her body fat ratio. The recommended minimum for women is 18 per cent. Hers is 2.6. "If she does it for too long, she'll pay the price for it," he says, but she doesn't hear. "I want to be the best in the world. I'll push and push and push and push, and if it means I get sick at the end, then I do."
As Vegas looms, she's already unwell. She's lost 30lb in three months. She has massages that tear her muscles so they'll grow back bigger. She's put through her gym paces by her friend Debbie, who looks like Sly Stallone and sounds like Tom Jones. "We're freaks in here!" Debbie shouts. Must be the drugs.
In fact for Joanna, the idea that all she does is pop pills is, the voice-over says, "a clear source of frustration and extreme irritation" (that'll be the 'roid rage). "Yeah, it's all about steroids," she says with heavy sarcasm. "We just take steroids and this is how we look. Try this at home for two or three weeks and see how you look." At least she doesn't deny having chemical help.
Her mother blames the judges. "If the winners have got to be that shape, that size, that bulk, they're going to do what they can. They're not going to get anywhere if they don't. Deep down, no one wants to do it." She looks away, bleakly.
"I'm hoping she'll get to the show," Dad says. "I'm hoping she'll win the show, and then I want to see what she's going to do with the rest of her life."
For now she'd like to live off sponsorship, but instead she depends on her website, "Joanna's Playhouse", which has 400 members paying $25 a month to see her in bikinis and micro dresses. On her webcam she jiggles about and bends over as the punters type in instant-message requests with their free hand.
In Atlanta for the Show of Strength, in which she needs to finish second to reach Miss Olympia, she's horribly malnourished, and for the last three days has drunk 45 sips of fluid a day. She's hollow-eyed and gaunt. Her scalp's peeling. But she mimes to "Barbie Girl", finishes runner-up and makes Vegas.
There, on the eve of the big night, she looks like Pete Doherty on a bender, and she's seriously feeble from the self-starving. In the gym, the camera artfully avoids showing what weights she's struggling to shift.
In the warm-up room there's more designer stubble than an episode of Miami Vice (jaw lines supplied by David Coulthard). On stage, Joanna is outshone. Next to her rivals she looks like a seven-stone weakling, and finishes seventh. Her lower body doesn't match her upper body, a judge says. So she can't retire yet. The war on herself continues.
"I'll just have to put a bit on my legs, that's all," she says. "I want to finish what I started, to justify the sacrifices I've made."
The rest of her life will have to wait. But not for too long, you're left hoping.Reuse content