"At 12.10pm he was taking a fitness class and he has gone and opened the window and stepped out onto the stairs.
"He fell to the concrete floor on the car park below. He sustained a ruptured spleen and a fractured hip."
The statement of facts, read by the judge, said the trainer was still suffering from his injuries.
"It is quite clear that this accident has had major effect on the victim and on his family. He suffered significant injuries that he is still to fully recover from and there is concerns that he may never recover from all of them.
"He is a very fit and active young man who is a crossfit trainer and who played many sports and now is very limited in his work and leisure activities.
"There is no doubt that he has suffered considerably and his lifestyle has been restricted, and will continue to be.
"He can no longer be a fireman, which was the job he wanted to do."
The judge said the sentence needed to send a strong message to those businesses involved, and others in New Zealand.
"This sentence needs to be imposed to make it very clear to these companies and to others that there are consequences for failing to fulfil their obligations under the Health and Safety Act."
Les Mills had already paid the man $13,560 and waived a $270 fee, so was ordered to pay the remaining $10,170 by November 15.
West Auckland Steel was no longer operating as a company, but the court was told its insurance would cover its $24,000 share.
He said both businesses had a legal obligation under the Health and Safety in Employment Act to take all practicable steps to ensure nobody was injured during its operations.
On the day of the accident West Auckland Steel's employee did not put a sign at the site, and no safety measures were taken by either party to mitigate the work being done.
The early admission of guilt and show of remorse lessened the reparations, said the judge.
In a statement, Les Mills Managing Director Dione Forbes-Ryrie said: "The company had pleaded guilty and fully accepts the ruling of the court and the fine and reparation payment imposed.
"Most importantly we will continue to support our valued team member who is still working with us.
"The safety of all those using our facilities is of paramount importance to us, which is why we conduct regular workplace safety assessments.
"A full investigation into our workplace safety has been conducted to ensure an incident of this nature does not occur again."
