Investment firm KKR has acquired California-based fitness chain The Bay Club for an undisclosed sum.

The Bay Club operates a collection of 22 "active lifestyle campuses", throughout California and has more than 50,000 members.

Founded in 1977, the company has been expanding its operations beyond fitness in recent years.

It has pivoted to hospitality and wellness by offering a diversity of services at its campuses and providing a range of high-end lifestyle amenities usually only found at luxury resorts. As well as racquet sports and fitness, it also offers full service spas at many of its properties.

According to Matthew Stevens, president and CEO of Bay Club, the new ownership will mean that The Bay Club will look to expand its reach outside its base in California.

"We're proud to have created California's leading active lifestyle community," said

"In partnering with KKR, we are excited to build even further on what we've accomplished thus far and bring our offering to even more communities across the country."

Nate Taylor, KKR's head of consumer retail team, added: "Bay Club's pioneering and differentiated model is one of the few scaled platforms in a large and highly fragmented health and wellness industry.

"Its members can find options that meet all of their - and their families' - needs."

US-based KKR manages multiple alternative asset classes, including private equity, energy, infrastructure, real estate and credit, with strategic manager partnerships that manage hedge funds.