MEC will start work immediately by supporting the business with media strategy planning and buying, digital marketing and below-the-line customer relationship marketing (CRM).
The Gym Group is planning to launch a member acquisition campaign in January that will promote a refreshed brand positioning.
The new positioning is being developed with Dinosaur, The Gym Group’s recently hired brand and creative agency.
The incumbent agency is Caburn Hope, and eCRM has previously been managed in-house.
Jim Graham, the chief operating officer at The Gym Group, said: "The rapid growth we have experienced in the past seven years – expanding from one gym to over 50 – has enabled us to develop a very robust, flexible and efficient marketing machine.
"But we need to continue to up our game, to cut through in an increasingly noisy and me-too market."
The Gym Group has also appointed Salesforce Marketing Cloud as its marketing automation provider.