U.K. gym chain Fitness First is further muscling into Asia with plans to open 50 new clubs over the next five years and invest around $140 million in the region, the firm announced Monday.

Fitness First Asia CEO Simon Flint told CNBC's "Squawk Box" that the firm planned to expand in Hong Kong, Indonesia, Malaysia, Singapore, Philippines and Thailand, with particular focus on Singapore and Thailand, the chain's strongest Asian markets. The chain currently operates 88 clubs across the six countries it is active in.