Fitness centre operator PureGym has apologised "unreservedly" for an "unacceptable" Facebook post from one of its gyms about slavery.
The Luton and Dunstable gym said "slavery was hard and so is this" regarding a workout designed to "celebrate black history month".
In a statement PureGym said the post was "wholly unacceptable" and "was not approved or endorsed by the company".
PureGym added it was removed "as soon as it was brought to our attention".
The company is the UK's largest gym chain by membership.
The workout, entitled "12 Years of Slave" after the Oscar-winning movie with a similar title, included 12 different moves such as burpees, push ups and box jumps.
Official statement from PureGym regarding an inappropriate post on the Luton & Dunstable gym social media channels. pic.twitter.com/c91xwHIogk— PureGym (@PureGym) October 5, 2020
Many users responded angrily to the gym's Facebook post with one saying PureGym had an "offensively tone-deaf marketing team" while another said it was "wrong, insensitive and horrendous on all levels".
PureGym said: "Each of our 271 gyms has its own social media channels which are run locally.
"We take this matter extremely seriously and are urgently investigating how and why this post was made."
The 2013 film 12 Years A Slave, starring Chiwetel Ejiofor, was based on the memoirs of Solomon Northup - a black musician sold into slavery in the US in 1841.
The Labour MP for Luton North, Sarah Owen, said on Twitter the "offensive advert shows exactly why we need Black History Month and why the Black Lives Matter movement is so important".