Fitness Holdings Northeast (FHN), one of the largest franchisees in the Crunch Fitness network, has secured growth investment from private equity group Synergy Capital.

The investment will fuel FHN's plans to launch and operate a 50-club network of Crunch gyms across the northeastern US.

It currently operates 18 locations in the region and is set to open four more locations in 2019.

According to Bob Cooke, FHN chief executive, the funding will enable the company to expand not only regionally, but also nationally through a mix of acquisitions and new developments.

"In seeking a partner, I wanted to find someone who shares FHN's ambition of becoming the largest franchise group in the country with at least 50 clubs in its name," Cooke said.

"It was apparent during talks with Synergy that they indeed share this vision. Our alignment in culture and values will make for a long-term, fruitful partnership."

Headquartered in New York City, Crunch Fitness opened its first site in 1989 and has since grown steadily and now has more than 300 gyms across five countries.

FHN's growth plans are in line with the larger plans to grow Crunch into one of the leading gym groups in the US.

Last month, Crunch CEO Keith Worts said the company expects to open "somewhere between 60 to 100 locations a year over the next five to 10 years".