A Boston-based private equity firm has made an undisclosed investment in the company behind the Masai Barefoot Technology (MBT) footwear brand.

Berkshire Partners LLC says its investment in Romanshorn, Switzerland-based Masai Group International will help accelerate and support the next phase of the company's growth.

Led by CEO Norbert Kraihamer and headquartered in Romanshorn, Switzerland, MBT designs athletic, casual and professional shoes and sandals that provide fitness and orthopaedic benefits including improved posture and relief from back pain and muscle and joint problems.

The footwear features an elliptical section or "Masai Sensor" underneath the heel, which creates an underfoot instability that stimulates and exercises the body's supporting muscle system. The product is available in over 20 countries including Germany, the UK and the US.

Berkshire's other investments include upmarket jeans maker Citizens of Humanity.