Shea was one of the United States' "Three Amigos" who swept the podium in the men's snowboard cross when it made its Paralympic debut at Sochi 2014.

"I never really had a chance to officially retire from my sport, so here it goes," he said on a post on Facebook on Thursday. 

Shea got into Para-snowboarding in 2010, eight years after losing his lower left leg in a wakeboarding accident.

Along with compatriots Keith Gabel and Evan Strong, he emerged as one of the top competitors in the sport in 2014.

He clinched the International Paralympic Committee Snowboard World Cup overall title in February of that year, with Strong second and Gabel fourth.

A month later at the Winter Paralympics, he took silver behind champion Strong and bronze medallist Gabel.

His success continued in later years, winning a world title in 2015 in the banked slalom and then finishing fourth in banked slalom and fifth in snowboard cross at the Pyeongchang 2018 Paralympics.

"One day my life was filled with red carpets, international travel, world class ski resorts and state of the art training facilities," Shea added.

"The next day I was in work boots and a hot workshop trying to plan out my future and my career."

Shea cited work issues, health problems and chronic injuries for his retirement.

"I had such a hard time letting go and because of that I felt like I never had the chance to officially say farewell," he wrote. 

"Retiring from sport can be a humbling experience to say the least. 

"Every athlete likes to think that they’ve left behind a legacy and I often questioned whether or not I did, especially when you see how quickly sport moves on without you. 

"The truth is that legacies don’t live on in sport, they live on in the individuals you interact with along the way."

Shea also won two bronze medals in snowboard cross at World Championships in 2012 and 2017.