The agencies were awarded the six-figure account following a competitive pitch.
KTB and Clinic have been given the responsibility of providing brand, marketing and PR consultancy on a retained and project-specific basis.
Clinic will work on redefining the brand's positioning and creating a new look for all aspects of Soho Gyms' communications. KTB will work closely with Clinic on brand and marketing activity, as well as undertaking all consumer, corporate and social media communications.
KTB's remit includes raising the awareness of the brand's profile within health and fitness titles and London media.
In addition, much of the agency's focus will be on creating a digital PR strategy, improving the brand's use of social media, as well as helping Soho Gyms engage with its members more effectively.
KTB specialises in sports, fitness and health. Other clients include Adidas, Technogym, The Ryder Cup and Help for Heroes.