The Gym Group expects results for 2017 to be in line with market forecasts with total revenue growth of 24.3%.
The group said total year end membership numbers were up by 35.5% at 607,000 (Dec 2016: 448,000) as the new openings and the existing estate traded strongly.
A trading update said: 'The business is in great shape to achieve the substantial growth in profitability included in its 2018 plans, as it benefits from the significant expansion of the past 2 years.'
Chief executive John Treharne said: 'This has been another year of accelerated, profitable growth with a record number of newly developed gyms (21) and the acquisition of the Lifestyle Fitness gyms.
'We are the fastest growing low-cost gym operator, have significantly increased market share and after 10 years of operation are still breaking records, underlining the resilience of our proposition and the constant evolution of our offer.
'We have had 100 million gym visits since launch in 2008, and our membership of over 600,000, would fit into Wembley, Twickenham, the Bernabeu, the MCG, Old Trafford, Croke Park and the Nou Camp combined.
'Looking ahead, we have a very strong foundation and a proven rollout model from which to build the business and increase its profitability further: we expect to open a further 15 - 20 new gyms in 2018 with more in the first half than in recent years.
'I have every confidence that our very experienced and innovative team is primed to deliver the next stage of our development.'