The 42-year-old, who is currently on maternity leave, revealed she is back on the fitness training after giving birth to her daughter Nancy.
Sharing a post-run selfie on Monday, Nina wrote: "First run since baby." She then added a close-up of her face and penned: "Absolutely horrible."
The post comes days after the mum-of-three revealed her experience with postnatal hair loss, which is very common among women.
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Alongside an image of herself cradling baby Nancy, the doting mum pointed to her "postnatal baldy bits" in the adorable snap. According to Patient UK, a number of women typically experience hair loss, which is caused by changing hormone levels, around three or four months after welcoming a baby.
Over the past few weeks, Nina has been sharing insights into her life as a mum-of-three. She is also a doting mum to two boys, who she shares with her husband Ted. Their eldest son, Digby, was born in 2016 and their second child, Michael, arrived two years later in 2018.
Speaking about welcoming the latest member of their family, Nina shared: "We've lost all sense of time as we've been feeding and snoozing and gazing and toe-stroking and head-smelling and marvelling at the absolute wonder of it all.
The line-up of BBC Breakfast presenters
The journalist joined BBC Breakfast back in 2006 and now hosts the show alongside Naga Munchetty from Thursday to Saturday. Prior to joining the BBC, Charlie was the principal anchor of Five News, fronting the programme's 9/11 coverage and Millennium celebrations.
The presenter joined the line-up of main presenters in 2014. Before landing a role on BBC Breakfast, she appeared on BBC World News, as well as BBC Two's weekday financial affairs programme, Working Lunch.
Sally has been a main presenter on the show since 2021, replacing Louise Minchin following her departure after 20 years. Sally previously worked as a sports presenter on the show and covered various major sporting events for the BBC, including Emma Raducanu's historic victory in the US Open tennis championship in 2021.
The newsreader and journalist took over from Dan Walker following his exit in 2022. He previously worked as a news correspondent for BBC News at Six and covered major events such as the 2012 London Olympics and the 2015 general election campaign.
Carol is the show's main weather presenter and has been waking up the nation with the weather forecast on the BBC for 30 years.
Nina is the show's main business presenter, having taken over from Steph McGovern in 2020. She often fills in as an anchor on the red sofa when the main hosts are absent.
Ben is a relief presenter and regularly stands in for the main hosts when they are away from the red sofa. He can also be seen on BBC News.
John is a sports presenter and has been working for the BBC since 2012, providing viewers will all the latest sports news and stories.
"It's been *haaaard* tho! A harder pregnancy. A tougher delivery and a longer recovery… maybe it's being older… but also I'd somehow forgotten."
Nina added: "I'd forgotten the anxiety of labour moving from the plan. I'd forgotten the swollen scars, bleeding breasts, mastitis fever, hormonal crashes, clots, constipation, codeine withdrawal, exhaustion…. And this time the added funk of a nosebleed (y tho?!).
"But part of getting older is getting better acquainted with your limits and letting go. I'm better at stopping and saying no to visitors and yes to a messy house and yes to asking for help. (A turning point was full snot crying down the phone to the GP - resulting in a glorious prescription of kind words, antibiotics, painkillers and a follow up call about how I was coping)."
Concluding her post, she wrote: "We are on the right track - for now - and enjoying life in the slow lane… usually with Australian MAFs & Italian red drinks… what a combo. Women and their bodies (parents or not) are complex and resilient that it fills me with immense pride. I can't wait to tell you all about it my sweet girl."