“You’re nothing. You’re a ghost, a fat ghost,” says the critical inner voice of disillusioned housewife Sheila Rubin, who spends her days booking rooms in cheap motels to binge on fast food.

Beautiful, thin, privileged; on the outside, her life appears perfect. But inside, Sheila, played by Rose Byrne, is battling a complex eating disorder and plodding through a humdrum life in the shadow of her husband, a man who wants his wife to cook, clean, and have threesomes.

And then she discovers the shiny, spandex-wrapped world of aerobics. “Only you have the power to change you” becomes a new mantra.

Set against the backdrop of sun-soaked 1980s San Diego, Byrne’s new series Physical is a dark comedy about a woman’s rise from dutiful wife to lifestyle guru, all the time while fighting her inner demons; it explores the pressures on women – and the pressures women place on themselves – to look a certain way.

The actress, best known for her role as alpha bridesmaid Helen in Bridesmaids, says Sheila is “an extreme version of the duality” of many women.

“She obviously has a terrible illness, an addiction that she’s living with, and we meet her at a breaking point,” Byrne tells Sky News. “But there is that idea of appearance; on the outside, she looks perfect and she’s skinny and pretty and white and all these things but yet she’s completely self-destructive inside. She has all these privileges… but yet it doesn’t matter.

“I think that is uniquely female in a way, having that kind of inner-destruction. Often I see depictions of, you know, external, and this and that – drinking and that kind of destructive side of women. But I feel like it’s often an inside job that we do.”

Physical shows that anyone can suffer from issues with their body image, no matter what they look like.

Created by Annie Weisman, known for her work on shows including Desperate Housewives, the story of Sheila’s eating disorder is based on the writer’s own experiences when she was younger.

“It’s uncomfortable and it’s not depicted [very often on screen],” says Byrne. “I don’t know, why it is that? I mean, it’s a hard thing to write about and it’s a hard thing to show. I don’t think it’s particularly something people gravitate toward. This is sort of an opportunity to start a conversation about it.”

Sheila’s story shows the “seediness of the illness and that addictive quality that it has”, Byrne adds. “Like any addiction, you know, it’s always: ‘That was the last time. I just had to do it one more time, and then I’m good and I won’t do it again.’ And you just keep falling back into this very destructive pattern.”

At first, it’s the exercise part of the aerobics that Sheila craves, but real empowerment comes when she harnesses the burgeoning technology of videotape to revolutionise the industry. While on-screen workouts are everywhere now, whether it’s celebrity DVDs or Instagram lives with wellness gurus, it all stemmed from the trend that emerged in the 1980s.

“It was really hard,” Byrne tells Sky News, of channelling her inner Jane Fonda. “You know, I’m not co-ordinated, I’m not a dancer. I’m lazy, essentially. So I really was daunted by this task.”

Weisman says she wanted to use the typically female space of aerobics as a force for empowerment.

“Having struggled for decades with eating disorders and feeling really disconnected from my body, aerobics and exercise were a place where you could really embrace a kind of strength and power,” she tells Sky News. “And like so many things that are specifically female spaces, I think it gets easily dismissed.

“Whether or not women – or men – have that specific struggle with food, I think a lot of people relate to the idea of having a kind of shameful secret, an obsessive habit that allows them to contain some really difficult and unmanageable feelings.

“We’re not interested in exploitation or anything lurid, but really just emotional truth. So I don’t think you have to have had an eating disorder to relate. But, you know, eating disorders certainly are a persistent threat in in our culture today.”

Another issue the show explores is the power dynamics between men and women.

Sheila masks her problems and her desires and is seemingly a meek and mild wife, taking a backseat to her husband as he bids for state assembly – but while her character lives in the background (at first, at least), Byrne is very much the star of the show.

The issue of female-led films and TV series has been highlighted in recent years as diversity in front of and behind the camera slowly improves, but it seems there are lots of male stars who aren’t happy about playing second fiddle to a woman.

“Worth knowing that one of the big reasons so many female-centred projects weren’t being made for so long wasn’t because they weren’t being written and commissioned but because they couldn’t find a bankable male star who would agree to play second string,” Succession and I Hate Suzie writer Lucy Prebble tweeted earlier in June.

And in February, actress and director Olivia Wilde made headlines for praising her reported boyfriend Harry Styles for taking a supporting role in her female-led film, Don’t Worry Darling, saying that “the industry has raised [male actors] to believe it lessens their power (i.e financial value) to accept these roles, which is one of the reasons it’s so hard to get financing for movies focusing on female stories”.

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Comedian and actor Rory Scovel, who plays Sheila’s husband Danny Rubin, says he was more than happy to play a supporting role alongside Byrne.

“I like being employed, first and foremost,” he tells Sky News. “So I would do probably anything. I don’t relate to the sentiment of needing to be the lead or feel as though I won’t play a supporting character to a female lead. I do understand that that is something and I do understand that some people make their decisions and feel that way, but I truthfully just can’t relate to it.

“I don’t know that I’m so concerned where [a] character falls in the line-up or who the lead actually is. I think it’s just exciting to get to be a part of a show that is so well written, telling such an interesting story. It’s already fun that it’s set in the ’80s and we get to wear those clothes and have that look, but also, in quite the opposite sentiment, to get to follow someone like Rose and see her in action…

“I find it to be an education that I need as an artist. I would rather see someone like her showing me literally from the front row how she operates and what she brings to her roles so that I can, you know, hopefully try to educate myself in whatever that is, so that I can be better. So yeah, I feel quite the opposite. I feel very grateful that I got to be a part of the show.”

Apple Original series Physical, starring Rose Byrne, premieres on Apple TV+ on Friday 18 June