While lots of her followers praised her "healthy body", the picture didn't come without criticism.
Some users questioned: "How the hell is that possible?", while another wrote: "Normal figures can't go back to what she has."
Erin hasn't wasted any time getting back into her active lifestyle since giving birth, and even went rock climbing last week.
Erin championed staying in shape while she was pregnant revealing in October: "I'm doing a little bit of yoga but mostly more high-intensity stuff."
She isn't the first celebrity to showcase her post baby body on Instagram - or come under fire for it. Last year, famed tennis player Mark Philippoussis' wife Silvana showcased her trim figure just two weeks after giving birth.
She captioned the snap: "Finally found the courage to post this...Me. 2 wks after giving birth! Ladies, I know every body's different but trust me when I say:- Don't forget to suck in your postpartum tummy's! It's the fastest most natural way to get your tummy back into shape:) I gave myself a few days to recover after birth then started sucking in a little everyday to get my stomach muscles working again- every little bit counts! #iamoldfashioned #forgetthewaistband #youcandoit #justdoit."
Kim Kardashian famously sparked the #belfie trend when she showed off her figure in a white swimsuit after giving birth to North West in 2013 and Miranda Kerr stunned the fashion pack in 2011 when she appeared on the catwalk just two months after giving birth.
But are these celebrity social media snaps realistic or are they just putting even more pressure on women to snap back into shape after giving birth?
Dr Natasha Bijlani, consultant psychiatrist at The Priory Hospital, Roehampton in south-west London, an expert in women's health and body image issues, said celebrities often painted an unrealistic picture of getting back into shape.
She said that revealing a dramatic post-pregnancy look had become common among the well-known, with many mothers insisting their weight somehow disappeared magically almost before they'd left the delivery room.
"Celebrities often portray an unrealistic image of how a new mother should expect to look soon after birth, and put undue pressure on tired new mothers, which is not what new mothers should be worrying about.
"They should be focused on spending time with their baby, recovering from the birth and getting as much rest as possible. The first six weeks after giving birth is referred to as the 'postnatal period' and it is usually inadvisable to do any exercise that is too strenuous for a number of reasons. During pregnancy, the body's ligaments loosen up in preparation for birth and it takes at least six weeks for everything to get back to normal, so you could end up damaging yourself if you start exercising too soon.
"In addition, a new mother should be focusing on bonding with her new baby, rather than worrying about her looks and body-shape. Essentially celebrities can paint an unrealistic picture of getting back into shape, definitely. For stars, their looks and image are paramount and the average woman should try not to be seduced into trying to emulate them."
- Daily Mail
